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RFC 1786 - Representation of IP Routing Policies in a Routing Re


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Network Working Group                                           T. Bates
Request for Comments: 1786            MCI Telecommunications Corporation
Category: Informational                                        E. Gerich
                                                             Merit, Inc.
                                                            L. Joncheray
                                                             Merit, Inc.
                                                          J-M. Jouanigot
                                                                    CERN
                                                           D. Karrenberg
                                                                RIPE NCC
                                                             M. Terpstra
                                                      Bay Networks, Inc.
                                                                   J. Yu
                                                             Merit, Inc.
                                                              March 1995

                 Representation of IP Routing Policies
                         in a Routing Registry
                              (ripe-81++)

Status of this Memo

   This memo provides information for the Internet community. This memo
   does not specify an Internet standard of any kind. Distribution of
   this memo is unlimited.

Abstract

   This document was originally published as a RIPE document known as
   ripe-181 but is also being published as an Informational RFC to reach
   a larger audience than its original scope. It has received community
   wide interest and acknowledgment throughout the Internet service
   provider community and will be used as the basic starting point for
   future work on Internet Routing Registries and routing policy
   representation.  It can also be referred to as ripe-81++.  This
   document is an update to the original `ripe-81'[1] proposal for
   representing and storing routing polices within the RIPE database. It
   incorporates several extensions proposed by Merit Inc.[2] and gives
   details of a generalized IP routing policy representation to be used
   by all Internet routing registries. It acts as both tutorial and
   provides details of database objects and attributes that use and make
   up a routing registry.

                           Table of Contents

   1. Introduction ................................................    3

   2. Organization of this Document ...............................    3

   3.  General Representation of Policy Information ...............    5

   4. The Routing Registry and the RIPE Database ..................   11

   5. The Route Object ............................................   16

   6. The Autonomous System Object ................................   26

   7. AS Macros ...................................................   36

   8. The Community Object ........................................   38

   9. Representation of Routing Policies ..........................   41

   10. Future Extensions ..........................................   50

   11. References .................................................   51

   12. Security Considerations ....................................   52

   13. Authors' Addresses .........................................   53

   Appendix A - Syntax for the "aut-num" object ...................   55

   Appendix B - Syntax for the "community" object .................   68

   Appendix C - Syntax for the "as-macro" object ..................   72

   Appendix D - Syntax for the "route" object .....................   76

   Appendix E - List of reserved words ............................   80

   Appendix F - Motivations for RIPE-81++ .........................   81

   Appendix G - Transition strategy ...............................   83

1.  Introduction

   This document is a much revised version of the RIPE routing registry
   document known as ripe-81 [1].  Since its inception in February, 1993
   and the establishment of the RIPE routing registry, several additions
   and clarifications have come to light which can be better presented
   in a single updated document rather than separate addenda.

   Some of the text remains the same the as the original ripe-81
   document keeping its tutorial style mixed with details of the RIPE
   database objects relating to routing policy representation.  However
   this document does not repeat the background and historical remarks
   in ripe-81. For these please refer to the original document.  It
   should be noted that whilst this document specifically references the
   RIPE database and the RIPE routing registry one can easily read
   "Regional routing registry" in place of RIPE as this representation
   is certainly general and flexible enough to be used outside of the
   RIPE community incorporating many ideas and features from other
   routing registries in this update.

   This document was originally published as a RIPE document known as
   ripe-181 but is also being published as an Informational RFC to reach
   a larger audience than its original scope. It has received large
   interest and acknowledgment within the Internet service provider
   community and will be used as the basic starting point for future
   work on Internet Routing Registries and routing policy
   representation.  It but can also be referred to as ripe-81++.

   We would like to acknowledge many people for help with this document.
   Specifically, Peter Lothberg who was a co-author of the original
   ripe-81 document for his many ideas as well as Gilles Farrache,
   Harvard Eidnes, Dale Johnson, Kannan Varadhan and Cengiz Alaettinoglu
   who all provided valuable input.  We would also like to thank the
   RIPE routing working group for their review and comment. Finally, we
   like to thank Merit Inc. for many constructive comments and ideas and
   making the routing registry a worldwide Internet service. We would
   also like to acknowledge the funding provided by the PRIDE project
   run in conjunction with the RARE Technical Program, RIPE and the RIPE
   NCC without which this paper would not have been possible.

2.  Organization of this Document

   This document acts as both a basic tutorial for understanding routing
   policy and provides details of objects and attributes used within an
   Internet routing registry to store routing policies. Section 3
   describes general issues about IP routing policies and their
   representation in routing registries. Experienced readers may wish to
   skip this section.  Section 4 provides an overview of the RIPE

   database, its basic concepts, schema and objects which make up the
   database itself.  It highlights the way in which the RIPE database
   splits routing information from allocation information.  Sections 5,
   6, 7 and 8 detail all the objects associated with routing policy
   representation.  Section 9 gives a fairly extensive "walk through" of
   how these objects are used for expressing routing policy and the
   general principles behind their use. Section 10 provides a list of
   references used throughout this document.  Appendix A, B, C and D
   document the formal syntax for the database objects and attributes.
   Appendix F details the main changes from ripe-81 and motivations for
   these changes. Appendix G tackles the issues of transition from
   ripe-81 to ripe-81++.

3.  General Representation of Policy Information

   Networks, Network Operators and Autonomous Systems

   Throughout this document an effort is made to be consistent with
   terms so as not to confuse the reader.

   When we talk about "networks" we mean physical networks which have a
   unique classless IP network number: Layer 3 entities. We do not mean
   organizations.

   We call the organizations operating networks "network operators".
   For the sake of the examples we divide network operators into two
   categories: "service providers" and "customers". A "service provider"
   is a network operator who operates a network to provide Internet
   services to different organizations, its "customers".  The
   distinction between service providers and customers is not clear cut.
   A national research networking organization frequently acts as a
   service provider to Universities and other academic organizations,
   but in most cases it buys international connectivity from another
   service provider. A University networking department is a customer of
   the research networking organization but in turn may regard
   University departments as its customers.

   An Autonomous System (AS) is a group of IP networks having a single
   clearly defined routing policy which is run by one or more network
   operators. Inside ASes IP packets are routed using one or more
   Interior Routing Protocols (IGPs). In most cases interior routing
   decisions are based on metrics derived from technical parameters like
   topology, link speeds and load.  The entity we refer to as an AS is
   frequently and more generally called a routing domain with the AS
   just being an implementation vehicle. We have decided to use the term
   AS exclusively because it relates more directly with the database
   objects and routing tools. By using only one term we hope to reduce
   the number of concepts and to avoid confusion. The academically
   inclined reader may forgive us.

   ASes exchange routing information with other ASes using Exterior
   Routing Protocols (EGPs).  Exterior routing decisions are frequently
   based on policy based rules rather than purely on technical
   parameters.  Tools are needed to configure complex policies and to
   communicate those policies between ASes while still ensuring proper
   operation of the Internet as a whole. Some EGPs like BGP-3 [8] and
   BGP-4 [9] provide tools to filter routing information according to
   policy rules and more. None of them provides a mechanism to publish
   or communicate the policies themselves. Yet this is critical for
   operational coordination and fault isolation among network operators
   and thus for the operation of the global Internet as a whole.  This

   document describes a "Routing Registry" providing this functionality.

   Routing Policies

   The exchange of routing information between ASes is subject to
   routing policies. Consider the case of two ASes, X and Y exchanging
   routing information:

                NET1 ......  ASX  <--->  ASY  ....... NET2

   ASX knows how to reach a network called NET1.  It does not matter
   whether NET1 is belonging to ASX or some other AS which exchanges
   routing information with ASX either directly or indirectly; we just
   assume that ASX knows how to direct packets towards NET1. Likewise
   ASY knows how to reach NET2.

   In order for traffic from NET2 to NET1 to flow between ASX and ASY,
   ASX has to announce NET1 to ASY using an external routing protocol.
   This states that ASX is willing to accept traffic directed to NET1
   from ASY. Policy thus comes into play first in the decision of ASX to
   announce NET1 to ASY.

   In addition ASY has to accept this routing information and use it.
   It is ASY's privilege to either use or disregard the information that
   ASX is willing to accept traffic for NET1. ASY might decide not to
   use this information if it does not want to send traffic to NET1 at
   all or if it considers another route more appropriate to reach NET1.

   So in order for traffic in the direction of NET1 to flow between ASX
   and ASY, ASX must announce it to ASY and ASY must accept it from ASX:

                    resulting packet flow towards NET1
                  <<===================================
                                    |
                                    |
                     announce NET1  |  accept NET1
                    --------------> + ------------->
                                    |
                        AS X        |    AS Y
                                    |
                     <------------- + <--------------
                       accept NET2  |  announce NET2
                                    |
                                    |
                   resulting packet flow towards NET2
                   ===================================>>

   Ideally, and seldom practically, the announcement and acceptance
   policies of ASX and ASY are identical.

   In order for traffic towards NET2 to flow, announcement and
   acceptance of NET2 must be in place the other way round. For almost
   all applications connectivity in just one direction is not useful at
   all.

   Usually policies are not configured for each network separately but
   for groups of networks.  In practise these groups are almost always
   defined by the networks forming one or more ASes.

   Routing Policy limitations

   It is important to realize that with current destination based
   forwarding technology routing policies must eventually be expressed
   in these terms. It is relatively easy to formulate reasonable
   policies in very general terms which CANNOT be expressed in terms of
   announcing and accepting networks. With current technology such
   policies are almost always impossible to implement.

   The generic example of a reasonable but un-implementable routing is a
   split of already joined packet streams based on something other than
   destination address.  Once traffic for the same destination network
   passes the same router, or the same AS at our level of abstraction,
   it will take exactly the same route to the destination (disregarding
   special cases like "type of service" routing, load sharing and

   routing instabilities).

   In a concrete example AS Z might be connected to the outside world by
   two links.  AS Z wishes to reserve these links for different kinds of
   traffic, let's call them black and white traffic.  For this purpose
   the management of AS Z keeps two lists of ASes, the black and the
   white list.  Together these lists comprise all ASes in the world
   reachable from AS Z.

                            "W"
                           <--->
                       ...           AS Z .... NET 3
                           <--->
                            "B"

   It is quite possible to implement the policy for traffic originating
   in AS Z: AS Z will only accept announcements for networks in white
   ASes on the white link and will only accept announcements for
   networks in black ASes on the black link.  This causes traffic from
   networks within AS Z towards white ASes to use the white link and
   likewise traffic for black ASes to use the black link.

   Note that this way of implementing things makes it necessary to
   decide on the colour of each new AS which appears before traffic can
   be sent to it from AS Z.  A way around this would be to accept only
   white announcements via the white link and to accept all but white
   announcements on the black link.  That way traffic from new ASes
   would automatically be sent down the black link and AS Z management
   would only need to keep the list of white ASes rather than two lists.

   Now for the unimplementable part of the policy.  This concerns
   traffic towards AS Z.  Consider the following topology:

           B AS ---)                    "W"
           W AS ---)                    --->
           B AS ---)>>  AS A  ---> ...           AS Z .... NET 3
           B AS ---)                    --->
           W AS ---)                    "B"

   As seen from AS Z there are both black and white ASes "behind" AS A.
   Since ASes can make routing decisions based on destination only, AS A
   and all ASes between AS A and the two links connecting AS Z can only
   make the same decision for traffic directed at a network in AS Z, say
   NET 3.  This means that traffic from both black and white ASes
   towards NET 3 will follow the same route once it passes through AS A.
   This will either be the black or the white route depending on the
   routing policies of AS A and all ASes between it and AS Z.

   The important thing to note is that unless routing and forwarding
   decisions can be made based on both source and destination addresses,
   policies like the "black and white" example cannot be implemented in
   general because "once joined means joined forever".

   Access Policies

   Access policies contrary to routing policies are not necessarily
   defined in terms of ASes. The very simplest type of access policy is
   to block packets from a specific network S from being forwarded to
   another network D. A common example is when some inappropriate use of
   resources on network D has been made from network S and the problem
   has not been resolved yet. Other examples of access policies might be
   resources only accessible to networks belonging to a particular
   disciplinary group or community of interest.  While most of these
   policies are better implemented at the host or application level,
   network level access policies do exist and are a source of
   connectivity problems which are sometimes hard to diagnose. Therefore
   they should also be documented in the routing registry according to
   similar requirements as outlined above.

   Routing vs. Allocation information

   The RIPE database contains both routing registry and address space
   allocation registry information. In the past the database schema
   combined this information. Because RIPE was tasked with running both
   an allocation and routing registry it seemed natural to initially
   combine these functions.  However, experience has shown that a clear
   separation of routing information from allocation is desirable. Often
   the maintainer of the routing information is not the same as the
   maintainer of the allocation information.  Moreover, in other parts
   of the world there are different registries for each kind of
   information.

   Whilst the actual routing policy objects will be introduced in the
   next section it is worthy of note that a transition from the current
   objects will be required. Appendix G details the basic steps of such
   a transition.

   This split in information represents a significant change in the
   representational model of the RIPE database. Appendix F expands on
   the reasons for this a little more.

   Tools

   The network operators will need a series of tools for policy routing.
   Some tools are already available to perform some of the tasks. Most
   notably, the PRIDE tools [3] from the PRIDE project started in
   September 1993 as well as others produced by Merit Inc [4] and CERN
   [5].

   These tools will enable them to use the routing policy stored in the
   RIPE routing registry to perform such tasks as check actual routing
   against policies defined, ensure consistency of policies set by
   different operators, and simulate the effects of policy changes.

   Work continues on producing more useful tools to service the Internet
   community.

4.  The Routing Registry and the RIPE Database

   One of the activities of RIPE is to maintain a  database  of European
   IP networks, DNS domains and their contact persons along with various
   other kinds of network management information. The database content
   is public and can be queried using the whois protocol as well as
   retrieved as a whole.  This supports NICs/NOCs all over Europe  and
   beyond  to  perform their respective tasks.

   The RIPE database combines both allocation registry and routing
   registry functions.  The RIPE allocation registry contains data about
   address space allocated to specific enterprises and/or delegated to
   local registries as well as data about the domain name space. The
   allocation registry is described in separate documents [6,7] and
   outside the scope of this document.

   Database Objects

   Each object in the database describes a single entity in the real
   world.  This  basic  principle  means that information about  that
   entity  should  only  be  represented  in   the corresponding
   database  object and not be repeated in other objects.  The whois
   service can automatically display referenced objects where
   appropriate.

   The types of objects stored in the RIPE database are summarized in
   the table below:

   R   Object      Describes                        References
   ____________________________________________________________________

   B   person      contact persons

   A   inetnum     IP address space                 person
   A   domain      DNS domain                       person

   R   aut-num     autonomous system                person
                                                    (aut-num,community)
   R   as-macro    a group of autonomous systems    person, aut-num
   R   community   community                        person
   R   route       a route being announced          aut-num, community

   R   clns        CLNS address space and routing   person

   The first column indicates whether the object is part of the
   allocation registry (A), the routing registry (R) or both (B).  The

   last column indicates the types of objects referenced by the
   particular type of object.  It can be seen that almost all objects
   reference contact persons.

   Objects are described by attributes  value  pairs,  one  per line.
   Objects  are  separated by empty lines. An attribute that consists of
   multiple lines should  have  the  attribute name  repeated on
   consecutive lines.  The information stored about network 192.87.45.0
   consists  of  three  objects,  one inetnum object and two person
   objects and looks like this:

   inetnum:   192.87.45.0
   netname:   RIPE-NCC
   descr:     RIPE Network Coordination Centre
   descr:     Amsterdam, Netherlands
   country:   NL
   admin-c:   Daniel Karrenberg
   tech-c:    Marten Terpstra
   rev-srv:   ns.ripe.net
   rev-srv:   ns.eu.net
   notify:    ops@ripe.net
   changed:   tony@ripe.net 940110
   source:    RIPE

   person:    Daniel Karrenberg
   address:   RIPE Network Coordination Centre (NCC)
   address:   Kruislaan 409
   address:   NL-1098 SJ Amsterdam
   address:   Netherlands
   phone:     +31 20 592 5065
   fax-no:    +31 20 592 5090
   e-mail:    dfk@ripe.net
   nic-hdl:   DK58
   changed:   ripe-dbm@ripe.net 920826
   source:    RIPE

   person:    Marten Terpstra
   address:   RIPE Network Coordination Centre (NCC)
   address:   PRIDE Project
   address:   Kruislaan 409
   address:   NL-1098 SJ Amsterdam
   address:   Netherlands
   phone:     +31 20 592 5064
   fax-no:    +31 20 592 5090
   e-mail:    Marten.Terpstra@ripe.net
   nic-hdl:   MT2
   notify:    marten@ripe.net
   changed:   marten@ripe.net 931230
   source:    RIPE

   Objects are stored and retrieved in this tag/value format.  The RIPE
   NCC does not provide differently formatted reports because any
   desired format can easily be produced from this generic one.

   Routing Registry Objects

   The main objects comprising the routing registry are "aut-num" and
   "route", describing an autonomous system and a route respectively. It
   should be noted that routes not described in the routing registry
   should never be routed in the Internet itself.

   The autonomous system (aut-num) object provides contact information
   for the AS and describes the routing policy of that AS.  The routing
   policy is described by enumerating all neighboring ASes with which
   routing information is exchanged.  For each neighbor the routing
   policy is described in terms of exactly what is being sent
   (announced) and allowed in (accepted).  It is important to note that
   this is exactly the part of the global policy over which an AS has
   direct control. Thus each aut-num object describes what can indeed be
   implemented and enforced locally by the AS concerned.  Combined
   together all the aut-num objects provide the global routing graph and
   permit to deduce the exact routing policy between any two ASes.

   While the aut-num objects describe how routing information is
   propagated, the route object describes a single route injected into
   the external routing mesh. The route object references the AS
   injecting (originating) the route and thereby indirectly provides
   contact information for the originating AS. This reference also
   provides the primary way of grouping routes into larger collections.
   This is necessary because describing routing policy on the level of
   single routes would be awkward to impractical given the number of
   routes in the Internet which is about 20,000 at the time of this
   writing.  Thus routing policy is most often defined for groups of
   routes by originating AS.  This method of grouping is well supported
   by current exterior routing protocols.  The route object also
   references community objects described below to provide another
   method of grouping routes.  Modification of aut-num object itself and
   the referencing by route objects is strictly protected to provide
   network operators control over the routing policy description and the
   routes originated by their ASes.

   Sometimes even keeping track of groups of routes at the AS level is
   cumbersome. Consider the case of policies described at the transit
   provider level which apply transitively to all customers of the
   transit provider. Therefore another level of grouping is provided by
   the as-macro object which provides groups of ASes which can be
   referenced in routing policies just like single ASes. Membership of
   as-macro groups is also strictly controlled.

   Sometimes there is a need to group routes on different criteria than
   ASes for purposes like statistics or local access policies. This is
   provided by the community object.  A community object is much like an

   AS but without a routing policy.  It just describes a group of
   routes. This is not supported at all by exterior routing protocols
   and depending on aggregation of routes may not be generally usable to
   define routing policies.  It is suitable for local policies and non-
   routing related purposes.

   These routing related objects will be described in detail in the
   sections below.

5.  The Route Object

   As stated in the previous chapter routing and address space
   allocation information are now clearly separated.  This is performed
   with the introduction of the route object. The route object will
   contain all the information regarding a routing announcement.

   All routing related attributes are removed from the inetnum object.
   Some old attributes are obsoleted: connect, routpr-l, bdryg-l, nsf-
   in, nsf-out, gateway).  The currently useful routing attributes are
   moved to the route object: aut-sys becomes origin, ias-int will be
   encoded as part of the inet-rtr [15] object and comm-list simply
   moves.  See [6] for detail of the "inetnum" object definition.

   The information in the old inetnum object

   inetnum:   192.87.45.0
   netname:   RIPE-NCC
   descr:     RIPE Network Coordination Centre
   descr:     Amsterdam, Netherlands
   country:   NL
   admin-c:   Daniel Karrenberg
   tech-c:    Marten Terpstra
   connect:   RIPE NSF WCW
   aut-sys:   AS3333
   comm-list: SURFNET
   ias-int:   192.87.45.80  AS1104
   ias-int:   192.87.45.6   AS2122
   ias-int:   192.87.45.254 AS2600
   rev-srv:   ns.ripe.net
   rev-srv:   ns.eu.net
   notify:    ops@ripe.net
   changed:   tony@ripe.net 940110
   source:    RIPE

   will be distributed over two objects:

   inetnum:   192.87.45.0
   netname:   RIPE-NCC
   descr:     RIPE Network Coordination Centre
   descr:     Amsterdam, Netherlands
   country:   NL
   admin-c:   Daniel Karrenberg
   tech-c:    Marten Terpstra
   rev-srv:   ns.ripe.net
   rev-srv:   ns.eu.net
   notify:    ops@ripe.net
   changed:   tony@ripe.net 940110
   source:    RIPE

   route:       192.87.45.0/24
   descr:       RIPE Network Coordination Centre
   origin:      AS3333
   comm-list:   SURFNET
   changed:     dfk@ripe.net 940427
   source:      RIPE

   The route object is used to represent a single route originated into
   the Internet routing mesh.  The actual syntax is given in Appendix D.
   However, there are several important aspects of the attributes worthy
   of note.

   The value of the route attribute will be a classless address.  It
   represents the exact route being injected into the routing mesh.  The
   representation of classless addresses is described in [10].

   The value of the origin attribute will be an AS reference of the form
   AS1234 referring to an aut-num object.  It represents the AS
   injecting this route into the routing mesh.  The "aut-num" object
   (see below) thus referenced provides all the contact information for
   this route.

   Special cases: There can only be a single originating AS in each
   route object.  However in todays Internet sometimes a route is
   injected by more than one AS. This situation is potentially dangerous
   as it can create conflicting routing policies for that route and
   requires coordination between the originating ASes.  In the routing
   registry this is represented by multiple route objects.

   This is a departure from the one route (net), one AS principle of the
   ripe-81 routing registry. The consequences for the different tools
   based in the routing registry will need to be evaluated and possibly
   additional consistency checking of the database is needed.

   The examples below will illustrate the usage of the route object
   further.  Suppose three chunks of address space of 2 different
   enterprises represented by the following inetnum objects:

   Examples

   inetnum:   193.0.1.0
   netname:   ENT-1
   descr:     Enterprise 1
    ...

   inetnum:   193.0.8.0
   netname:   ENT-2
   descr:     Enterprise 2
    ...

   inetnum:   193.0.9.0
   netname:   ENT-2-SPEC
   descr:     Enterprise 2
    ...

   Supposing that the Enterprises have their own AS numbers straight
   application of routing without aggregation would yield:

   route:       193.0.1.0/24
   descr:       Enterprise 1
   origin:      AS1
    ...

   route:       193.0.8.0/24
   descr:       Enterprise 2
   origin:      AS2
    ...

   route:       193.0.9.0/24
   descr:       Enterprise 2
   origin:      AS2
    ...

   NB: This representation can be achieved by straight translation from
   the ripe-81 representation. See Appendix G for more details.

   Homogeneous Aggregation

   The two chunks of address space of Enterprise 2 can be represented by
   one aggregate route turning two route objects into one and
   potentially saving routing table space for one route.

   route:       193.0.8.0/23
   descr:       Enterprise 2
   origin:      AS2
    ...

   Note that AS2 can also decide to originate all routes mentioned so
   far, two 24-bit prefixes and one 23-bit prefix. This case would be
   represented by storing all three route objects in the database. In
   this particular example the additional routes will not add any
   functionality however and only increase the amount of routes
   announced unnecessarily.

   Heterogeneous Aggregation

   Consider the following case however:

   route:       193.0.8.0/24
   descr:       Enterprise 2
   origin:      AS2
    ...

   route:       193.0.9.0/24
   descr:       Enterprise 2 / Special
   origin:      AS2
   comm-list:   SPECIAL
    ...

   Now the prefix 193.0.9.0/24 belongs to community SPECIAL (this
   community may well not be relevant to routing) and the other prefix
   originated by AS2 does not. If AS2 aggregates these prefixes into the
   193.0.8.0/23 prefix, routing policies based on the community value
   SPECIAL cannot be implemented in general, because there is no way to
   distinguish between the special and the not-so-special parts of AS2.

   If another AS has the policy to accept only routes to members of
   community SPECIAL it cannot implement it, because accepting the route
   to 193.0.8.0/23 would also route to 193.0.8.0/24 and not accepting
   this route would lose connectivity to the special part 193.0.9.0/24.
   We call aggregate routes consisting of components belonging to
   different communities or even different ASes "heterogeneous
   aggregates".

   The major problem introduced with heterogeneous aggregates is that
   once the homogeneous more specific routes are withdrawn one cannot
   tell if a more specific part of the heterogeneous route has a
   different policy. However, it can be counter argued that knowing this
   policy is of little use since a routing policy based on the less
   specific heterogeneous aggregate only cannot be implemented. In fact,
   this displays a facet of CIDR itself in that one may actually trade
   off implementing slight policy variations over announcing a larger
   (albeit heterogeneous in terms of policy) aggregate to save routing
   table space.

   However, it is still useful to be able to document these variations
   in policy especially when this homogeneous more specific route is
   just being withdrawn. For this one can use the "withdrawn" attribute.
   The withdrawn attribute can serve to both indicate that a less
   specific aggregate is in fact heterogeneous and also allow the
   general documenting of route withdrawal.

   So there has to be a way for AS2 to document this even if it does not
   originate the route to 193.0.9.0/24 any more.  This can be done with
   the "withdrawn" attribute of the route object.  The aggregate route
   to 193.0.8.0/23 is now be registered as:

   route:       193.0.8.0/23
   descr:       Enterprise 2
   origin:      AS2
    ...

   With the two homogeneous routes marked as withdrawn from the Internet
   routing mesh but still preserving their original routing information.

   route:       193.0.8.0/24
   descr:       Enterprise 2
   origin:      AS2
   withdrawn:   940701
    ...

   route:       193.0.9.0/24
   descr:       Enterprise 2 / Special
   origin:      AS2
   comm-list:   SPECIAL
   withdrawn:   940701
    ...

   It should be noted that the date value used in the withdrawn
   attribute can only be in the past.

   Proxy Aggregation

   The next step of aggregation are aggregates consisting of more than
   one AS. This generally means one AS is aggregating on behalf of
   another. It is called proxy aggregation. Proxy aggregation should be
   done with great care and always be coordinated with other providers
   announcing the same route.

   Consider the following:

   route:       193.0.0.0/20
   descr:       All routes known by AS1 in a single package
   origin:      AS1
    ...

   route:       193.0.1.0/24
   descr:       Foo
   origin:      AS1
   withdrawn:   940310
    ...

   route:       193.0.8.0/24
   descr:       Bar
   origin:      AS2
   withdrawn:   940310
    ...

   route:       193.0.9.0/24
   descr:       Bar-2
   origin:      AS2
   withdrawn:   940310
   comm-list:   SPECIAL
    ...

   If AS1 announced no other routes to a single homed neighboring AS,
   that neighbor can in general either take that route or leave it but
   not differentiate between AS1 and AS2.

   Note: If the neighbor was previously configured to accept routes
   originating in AS2 but not in AS1 they lose connectivity to AS2 as
   well.  This means that proxy aggregation has to be done carefully and
   in a well coordinated fashion. The information in the withdrawn route
   object can help to achieve that.

   Aggregates with Holes

   If we assume that the world of our example still consists of only
   three chunks of address space the aggregate above contains what are
   called holes, parts of an aggregate that are not reachable via the
   originator of the route.  From the routing information itself one
   cannot tell whether these are holes and what part of the route falls
   inside one.  The only way to tell is to send a packet there and see
   whether it gets to the destination, or an ICMP message is received
   back, or there is silence.  On the other hand announcing aggregates
   with holes is quite legitimate.  Consider a 16-bit aggregate with
   only one 24-bit prefix unreachable.  The savings in routing table
   size by far outweigh the hole problem.

   For operational reasons however it is very useful to register these
   holes in the routing registry. Consider the case where a remote
   network operator experiences connectivity problems to addresses

   inside an aggregate route.  If the packets are getting to the AS
   announcing the aggregate and there are no more specific routes, the
   normal cause of action is to get in touch with the originating AS of
   the aggregate route and ask them to fix the problem. If the address
   falls into a hole this is futile. Therefore problem diagnosis can be
   sped up and unnecessary calls prevented by registering the holes in
   the routing registry. We do this by using the "hole" attribute. In
   our example the representation would be:

   route:       193.0.0.0/20
   descr:       All routes known by AS1
   origin:      AS1
   hole:        193.0.0.0/24
   hole:        193.0.2.0/23
   hole:        193.0.4.0/22
   hole:        193.0.10.0/23
   hole:        193.0.12.0/22
    ...

   Note: there would also be two routes with the withdrawn attribute as
   displayed above (i.e. 193.0.8.0/24 and 193.0.9.0/24).  It is not
   mandatory to document all holes. It is recommended all holes routed
   by another service provider are documented.

   Multiple Proxy Aggregation

   Finally suppose that AS2 decides to announce the same aggregate, as
   in the previous example, they would add the following route object to
   the registry:

   route:       193.0.0.0/20
   descr:       All routes known by AS2
   origin:      AS2
   hole:        193.0.0.0/24
   hole:        193.0.2.0/23
   hole:        193.0.4.0/22
   hole:        193.0.10.0/23
   hole:        193.0.12.0/22
    ...

   Both AS1 and AS2 will be notified that there already is a route to
   the same prefix in the registry.

   This multiple proxy aggregation is very dangerous to do if the sub-
   aggregates of the route are not the same. It is still dangerous when
   the sub-aggregates are consistent but connectivity to the sub-
   aggregates varies widely between the originators.

   Route object update procedures

   Adding a route object will have to be authorised by the maintainer of
   the originating AS. The actual implementation of this is outside the
   scope of this document.  This guarantees that an AS guardian has full
   control over the registration of the routes it announces [11].

   What is an Inter-AS network ?

   An inter-AS network (Inter-AS IP networks are those networks are
   currently called FIXes, IXFs, DMZs, NAPs, GIX and many other
   acronyms) exists for the purpose of passing traffic and routing
   information between different autonomous systems.  The most simple
   example of an inter-AS network is a point-to-point link, connecting
   exactly two ASes.  Each end of such a link is connected to an
   interface of router belonging to each of the autonomous systems.
   More complex examples are broadcast type networks with multiple
   interfaces connecting multiple ASes with the possibility of more than
   one connection per AS.  Consider the following example of three
   routers 1, 2 and 3 with interfaces a through f  connected by two
   inter-AS networks X and Y:

                              X              Y
                     a1b     ---    c2d     ---    e3f

   Suppose that network X is registered in the routing registry as  part
   of AS1 and net Y as part of AS3. If traffic passes from left to right
   prtraceroute will report the following  sequence  of  interfaces  and
   ASes:

           a in AS1
           c in AS1
           e in AS3

   The traceroute algorithm enumerates only the receiving interfaces on
   the way to the destination.  In the example this leads to the passage

   of AS2 going unnoticed.  This is confusing to the user and will also
   generate exceptions when the path found is checked against the
   routing registry.

   For operational monitoring tools such as prtraceroute it is necessary
   to know which interface on an inter-AS network belongs to which AS.
   If AS information is not known about interfaces on an inter-AS
   network, tools like prtraceroute cannot determine correctly which
   ASes are being traversed.

   All interfaces on inter-AS networks will are described in a separate
   object know as the `inet-rtr' object [15].

6.  The Autonomous System Object

   Autonomous Systems

   An Autonomous System (AS) is a group of IP networks operated by one
   or more network operators which has a single and clearly defined
   external routing policy.

   An AS has a unique number associated with it which is used both in
   exchange of exterior routing information and as an identifier of the
   AS itself.  Exterior routing protocols such as BGP and EGP are used
   to exchange routing information between ASes.

   In routing terms an AS will normally use one or more interior gateway
   protocols (IGPs) in conjunction with some sort of common agreed
   metrics when exchanging network information within its own AS.

   The term AS is often confused or even misused as a convenient way of
   grouping together a set of networks which belong under the same
   administrative umbrella even if within that group of networks there
   are various different routing policies.  We provide the "community"
   concept for such use.  ASes can strictly have only one single
   external routing policy.

   The creation of an AS should be done in a conscious and well
   coordinated manner to avoid creating ASes for the sake of it, perhaps
   resulting in the worst case scenario of one AS per routing
   announcement.  It should be noted that there is a limited number of
   AS numbers available. Also creating an AS may well increase the
   number of AS paths modern EGPs will have to keep track of. This
   aggravates what is known as "the routing table growth problem".  This
   may mean that by applying the general rules for the creation and
   allocation of an AS below, some re-engineering may well be needed.
   However, this may be the only way to actually implement the desired
   routing policy anyway.  The creation and allocation of an AS should
   be done with the following recommendations in mind:

    +   Creation of an AS is only required when exchanging routing
        information with other ASes.  Some router implementations make
        use of an AS number as a form of tagging to identify the routing
        process.  However, it should be noted that this tag does not
        need to be unique unless routing information is indeed exchanged
        with other ASes.

    +   For a simple case of customer networks connected to a single
        service provider, the IP network should normally be a member of
        the service providers AS. In terms of routing policy the IP
        network has exactly the same policy as the service provider and
        there is no need to make any distinction in routing information.
        This idea may at first seem slightly alien to some, but it
        highlights the clear distinction in the use of the AS number as
        a representation of routing policy as opposed to some form of
        administrative use.

    +   If a network operator connects to more than one AS with
        different routing policies then they need to create their own
        AS.  In the case of multi-homed customer networks connected to
        two service providers there are at least two different routing
        policies to a given customer network.  At this point the
        customer networks will be part of a single AS and this AS would
        be distinct from either of the service providers ASes.  This
        allows the customer the ability of having a different
        representation of policy and preference to the different service
        providers.  This is the ONLY case where a network operator
        should create its own AS number.

    +   As a general rule one should always try to populate the AS with
        as many routes as possible, providing all routes conform to the
        same routing policy.

   Each AS is represented in the RIPE database by both an aut-num object
   and the route objects representing the routes originated by the AS.
   The aut-num object stores descriptive, administrative and contact
   information about the AS as well as the routing policies of the AS in
   relation to all neighboring ASes.

   The origin attributes of the route  objects define the set of routes
   originated by the AS. Each route object can have exactly one origin
   attribute.  Route objects can only be created and updated by the
   maintainer of the AS and not by those immediately responsible for the
   particular routes referenced therein.  This ensures that operators,
   especially service providers, remain in control of AS routing
   announcements.

   The AS object itself is used to represent a description of
   administrative details and the routing policies of the AS itself. The
   AS object definition is depicted as follows.

   Example:

   aut-num:  AS1104
   descr:    NIKHEF-H Autonomous system
   as-in:    from AS1213 100 accept AS1213
   as-in:    from AS1913 100 accept AS1913
   as-in:    from AS1755 150 accept ANY
   as-out:   to AS1213 announce ANY
   as-out:   to AS1913 announce ANY
   as-out:   to AS1755 announce AS1104 AS1913 AS1213
   tech-c:   Rob Blokzijl
   admin-c:  Eric Wassenaar
   guardian: as-guardian@nikhef.nl
   changed:  ripe-dbm@ripe.net 920910
   source:   RIPE

   See Appendix A for a complete syntax definition of the "aut-num"
   object.

   It should be noted that this representation provides two things:

       + a set of routes.

       + a description of administrative details and routing policies.

   The set of routes can be used to generate network list based
   configuration information as well as configuration information for
   exterior routing protocols knowing about ASes. This means an AS can
   be defined and is useful even if it does not use routing protocols
   which know about the AS concept.

   Description of routing policies between ASs with multiple connections
   - "interas-in/interas-out"

   The following section is only relevant for ASes which use different
   policies on multiple links to the same neighboring AS. Readers not
   doing this may want to skip this section.

   Description of multiple connections between ASs defines how two ASs
   have chosen to set different policies for the use of each or some of
   the connections between the ASs.  This description is necessary only
   if the ASs are connected in more than one way and the routing policy
   and differs at these two connections.

   Example:

                   LINK1
      193.0.1.1 +----------+ 193.0.1.2
                |          |
   AS1------AS2==           ==AS3-----AS4
                |          |
      193.0.1.5 +----------+ 193.0.1.6
                    LINK2

        Note: LINK here denotes the peer connection points between
        ASs.  It is not necessarily just a serial link.  It could
        be ethernet or any other type of connection as well.  It
        can also be a peer session where the address is the same at
        one end and different at the other end.

   It may be that AS2 wants to use LINK2 only for traffic towards AS4.
   LINK1 is used for traffic to AS3 and as backup to AS4, should LINK2
   fail.  To implement this policy, one would use the attribute
   "interas-in" and "interas-out."  This attribute permits ASs to
   describe their local decisions based on its preference such as
   multi-exit-discriminators (MEDs) as used in some inter-domain routing
   protocols (BGP4, IDRP) and to communicate those routing decisions.
   This information would be useful in resolving problems when some
   traffic paths changed from traversing AS3's gateway in Timbuktu
   rather than the gateway in Mogadishu.  The exact syntax is given in
   Appendix A.  However, if we follow this example through in terms of
   AS2 we would represent this policy as follows:

   Example:

   aut-num: AS2
   as-in: from AS3 10 accept AS3 AS4
   as-out: to AS3 announce AS1 AS2
   interas-in:from AS3 193.0.1.1/32 193.0.1.2/32 (pref=5) accept AS3
   interas-in:from AS3 193.0.1.1/32 193.0.1.2/32 (pref=9) accept AS4
   interas-in:from AS3 193.0.1.5/32 193.0.1.6/32 (pref=7) accept AS4
    ...

   Here we see additional policy information between two ASs in terms of
   the IP addresses of the connection.  The parentheses and keyword are
   syntactic placeholders to add the readability of the attributes.  If
   pref=MED is specified the preference indicated by the remote AS via
   the multi-exit- discriminator metric such as BGP is used.  Of course
   this type on inter-AS policy should always be bilaterally agreed upon
   to avoid asymmetry and in practice there may need  to be
   corresponding interas-out attributes in the policy representation of
   AS3.

   The interas-out attribute is similar to interas-in as as-out is to
   as-in.  The one major difference being that interas-out allows you to
   associate an outgoing metric with each route. It is important to note
   that this metric is just passed to the peer AS and it is at the peer
   AS's discretion to use or ignore it.  A special value of IGP
   specifies that the metric passed to the receiving AS will be derived
   from the IGP of the sending AS. In this way the peer AS can choose
   the optimal link for its traffic as determined by the sending AS.

   If we look at the corresponding interas-out for AS3 we would see the
   following:

   Example:

aut-num: AS3
as-in: from AS2 10 accept AS1 A2
as-out: to AS2 announce AS3 AS4
interas-out:to AS2 193.0.1.2/32 193.0.1.1/32 (metric-out=5) announce AS3
interas-out:to AS2 193.0.1.2/32 193.0.1.1/32 (metric-out=9) announce AS4
interas-out:to AS2 193.0.1.6/32 193.0.1.5/32 (metric-out=7) announce AS4
 ...

   Descriptions of interas policies do  not  replace  the  global
   policy described  in as-in, as-out and other policy attributes which
   should be specified too.  If the global policy mentions  more  routes
   than the combined local policies then local preferences for these
   routes are assumed to be equal for all links.

   Any route specified in interas-in/out and not specified in as-in/out
   is assumed not accepted/announced between the ASes concerned.
   Diagnostic tools should flag this inconsistency as an error.  It
   should be noted that if an interas-in or interas-out policy is
   specified then it is mandatory to specify the corresponding global
   policy in the as-in or as-out line. Please note there is no relevance
   in the cost associated with as-in and the preferences used in
   interas-in.

   The interaction of interas-in/interas-out with as-in/as-out

   Although formally defined above, the rules associated with policy
   described in terms of interas-in and interas-out with respect to as-
   in and as-out are worthy of clarification for implementation.

   When using interas-in or interas-out policy descriptions, one must
   always make sure the set of policies described between two ASes is
   always equal to or a sub-set of the policy described in the global
   as-in or as-out policy. When a sub-set is described remember the
   remaining routes are implicitly shared across all connections. It is
   an error for the interas policies to describe a superset of the
   global policies, i.e. to announce or accept more routes than the
   global policies.

   When defining complex interas based policies it is advisable to
   ensure that any possible ambiguities are not present by explicitly
   defining your policy with respect to the global as-in and as-out
   policy.

   If we look at a simple example, taking just in-bound announcements to
   simplify things. If we have the following global policy:

   aut-num: AS1
   as-in: from AS2 10 accept AS100 OR {10.0.0.0/8}

   Suppose there are three peerings between AS1 and AS2, known as L1-R1,
   L2-R2 and L3-R3 respectively. The actual policy of these connections
   is to accept AS100 equally on these three links and just route
   10.0.0.0/8 on L3-R3. The simple way to mention this exception is to
   just specify an interas policy for L3-R3:

   interas-in: from AS2 L3 R3 (pref=100) accept {10.0.0.0/8}

   The implicit rule that all routes not mentioned in interas policies
   are accepted on all links with equal preference ensures the desired
   result.

   The same policy can be written explicitly as:

   interas-in: from AS2 L1 R1 (pref=100) accept AS100
   interas-in: from AS2 L2 R2 (pref=100) accept AS100
   interas-in: from AS2 L3 R3 (pref=100) accept AS100 OR {10.0.0.0/8}

   Whilst this may at first sight seem obvious, the problem arises when
   not all connections are mentioned. For example, if we specified only
   an interas-in line for L3-R3 as below:

   aut-num: AS1
   as-in: from AS2 10 accept AS100 OR {10.0.0.0/8}
   interas-in: from AS2 L3 R3 (pref=100) accept AS100 OR {10.0.0.0/8}

   then the policy for the other links according to the rules above
   would mean they were equal to the global policy minus the sum of the
   local policies (i.e. ((AS100 OR {10.0.0.0/0}) / (AS100 OR
   {10.0.0.0/0})) = empty) which in this case would mean nothing is
   accepted on connections L1-R1 and L2-R2 which is incorrect.

   Another example: If we only registered  the  policy  for  link  L2-
   R2:

   interas-in: from AS2 L2 R2 (pref=100) accept AS100

   The implicit policy for both L1-R1 and L3-R3 would be as follows:

   interas-in: from AS2 L1 R1 (pref=100) accept {10.0.0.0/8}
   interas-in: from AS2 L3 R3 (pref=100) accept {10.0.0.0/8}

   This is derived as the set of global policies minus the set of
   interas-in policies (in this case just accept AS100 as it was the
   L2-R2 interas-in policy we registered) with equal cost for the
   remaining connection. This again is clearly not what was intended.

   We strongly recommend that you always mention all policies for all
   interas connections explicitly, to avoid these possible errors. One
   should always ensure the set of the interas policies is equal to the
   global policy. Clearly if interas policies differ in complex ways it
   is worth considering splitting the AS in question into separate ASes.
   However, this is beyond the direct scope of this document.

   It should also be noted there is no direct relationship between the
   cost used in as-in and the preference used in interas-in.

   How to describe the exclusion policy of a certain AS - "as-exclude"

   Some ASes have a routing policy based on the exclusion of certain
   routes if for whatever reason a certain AS is used as transit.
   Whilst, this is in general not good practice as it makes implicit
   assumptions on topology with asymmetry a possible outcome if not
   coordinated, this case needs to be accommodated within the routing
   policy representation.

   The way this is achieved is by making use of the "as-exclude"
   attribute. The precise syntax of this attribute can be found in
   Appendix A along with the rest of the defined syntax for the "aut-
   num" object. However, some explanation of the use of this attribute
   is useful. If we have the following example topology.

   Example:

              AS4--------AS3
    |          |          |
    |          |          |
   AS1--------AS2--------AS5

   With a simple corresponding policy like so:

   Example:

   aut-num: AS1
   as-in:  from AS2 100 accept ANY
   as-out: to AS2 announce AS1
   as-exclude: exclude AS4 to ANY
    ....

   We see an interesting policy. What this says in simple terms is AS1
   doesn't want to reach anything if it transits AS4. This can be a
   perfectly valid policy. However, it should be realized that if for
   whatever reason AS2 decides to route to AS3 via AS4 then immediately
   AS1 has no connectivity to AS3 or if AS1 is running default to AS2
   packets from AS1 will still flow via AS4. The important point about
   this is that whilst AS1 can advise its neighbors of its policy it has
   no direct control on how it can enforce this policy to neighbors
   upstream.

   Another interesting scenario to highlight the unexpected result of
   using such an "as-exclude" policy. If we assume in the above example
   AS2 preferred AS4 to reach AS3 and AS1 did not use default routing
   then as stated AS1 would have no connectivity to AS3. Now lets
   suppose that for example the link between AS2 and AS4 went down for
   some reason. Like so:

   Example:

              AS4--------AS3
                          |
                          |
   AS1--------AS2--------AS5

   Suddenly AS1 now has connectivity to AS3. This unexpected behavior
   should be considered when created policies based on the "as-exclude"
   attribute.

   The second problem with this type of policy is the potential of
   asymmetry. In the original example we saw the correct policy from
   AS1's point of view but if ASes with connectivity through AS4 do not
   use a similar policy you have asymmetric traffic and policy.  If an
   AS uses such a policy they must be aware of the consequences of its
   use. Namely that the specified routes which transit the AS (i.e.
   routing announcements with this AS in the AS path information) in
   question will be excluded.  If not coordinated this can easily cause
   asymmetry or even worse loss of connectivity to unknown ASes behind
   (or in front for that matter) the transit AS in question.  With this
   in mind this attribute can only be viewed as a form of advisory to
   other service providers. However, this does not preclude its use with
   policy based tools if the attribute exists.

   By having the ability to specify a route keyword based on any of the
   four notations given in the syntax it allows the receiving AS to
   specify what routes it wishes to exclude through a given transit AS
   to a network granularity.

7.  AS Macros

   It may be difficult to keep track of each and every new AS that is
   represented in the routing registry.  A convenient way around this is
   to define an `AS Macro' which essentially is a convenient way to
   group ASes. This is done so that each and every AS guardian does not
   have to add a new AS to it's routing policy as described by the as-in
   and as-out attributes of it's AS object.

   However, it should be noted that this creates an implicit trust on
   the guardian of the AS-Macro.

   An AS-Macro can be used in <routing policy expressions> for the "as-
   in" and "as-out" attributes in the aut-num object. The AS-Macro
   object is then used to derive the list or group of ASes.

   A simple example would be something like:

   Example:

   aut-num: AS786
   as-in:   from AS1755 100 accept AS-EBONE AND NOT AS1104
   as-out   to AS1755 announce AS786
    .....

   Where the as-macro object for AS-EBONE is as follows:

   as-macro:  AS-EBONE
   descr:     ASes routed by EBONE
   as-list:   AS2121 AS1104 AS2600 AS2122
   as-list:   AS1103 AS1755 AS2043
   guardian:  guardian@ebone.net
    ......

   So the policy would be evaluated to:

   aut-num: AS786
   as-in:   from AS1755 100 accept (AS2121 OR AS1104 OR AS2600 OR AS2122
   as-in:   from AS1755 100 accept AS1103 OR AS1755 OR
   as-in:   from AS1755 100 accept AS2043) AND NOT AS1104
    ......

   It should be noted that the above examples incorporates the rule for
   line wrapping as defined in Appendix A for policy lines.  See
   Appendix C for a definition on the AS-Macro syntax.

8.  The Community Object

   A community is a group of routes that cannot be represented by an AS
   or a group of ASes.  It is in some circumstances useful to define a
   group of routes that have something in common.  This could be a
   special access policy to a supercomputer centre, a group of routes
   used for a specific mission, or a disciplinary group that is
   scattered among several autonomous systems.  Also these communities
   could be useful to group routes for the purpose of network
   statistics.

   Communities do not exchange routing information, since they do not
   represent an autonomous system.  More specifically, communities do
   not define routing policies, but access or usage policies. However,
   they can be used as in conjunction with an ASes routing policy to
   define a set of routes the AS sets routing policy for.

   Communities should be defined in a strict manner, to avoid creating
   as many communities as there are routes, or even worse.  Communities
   should be defined following the two rules below;

    +   Communities must have a global meaning.  Communities that have
        no global meaning, are used only in a local environment and
        should be avoided.

    +   Communities  must not be defined to express non-local policies.
        It should be avoided that a community is created because some
        other organization forces a policy upon your organization.
        Communities must only be defined to express a policy defined by
        your organization.

   Community examples

   There are some clear examples of communities:

   BACKBONE -
        all customers of a given backbone service provider even though
        they can have various different routing policies and hence
        belong to different ASes. This would be extremely useful for
        statistics collection.

   HEPNET -
        the High Energy Physics community partly shares infrastructure
        with other organizations, and the institutes it consists of are
        scattered all over Europe, often being part of a non HEPNET
        autonomous system. To allow statistics, access or part of a
        routing policy , a community HEPNET, consisting of all routes
        that are part of HEPNET, conveniently groups all these routes.

   NSFNET -
        the National Science Foundation Network imposes an acceptable
        use policy on routes that wish to make use of it. A community
        NSFNET could imply the set of routes that comply with this
        policy.

   MULTI -
        a large multinational corporation that does not have its own
        internal infrastructure, but connects to the various parts of
        its organizations by using local service providers that connect
        them all together, may decide to define a community to restrict
        access to their networks, only by networks that are part of this
        community. This way a corporate network could be defined on
        shared infrastructure. Also, this community could be used by any
        of the service providers to do statistics for the whole of the
        corporation, for instance to do topology or bandwidth planning.

   Similar to Autonomous systems, each community is represented in the
   RIPE database by both a community object and community tags on the
   route objects representing the routes belonging to the community.
   The community object stores descriptive, administrative and contact
   information about the community.

   The community tags on the route objects define the set of routes
   belonging to a community.  A route can have multiple community tags.
   The community tags can only be created and updated by the "guardian"
   of the community and not by those directly responsible for the
   particular network.  This ensures that community guardians remain in
   control of community membership.

   Here's an example of how this might be represented in terms of the
   community tags within the network object.  We have an example where
   the route 192.16.199.0/24 has a single routing policy (i.e.  that of
   AS 1104), but is part of several different communities of interest.
   We use the tag "comm-list" to represent the list of communities
   associated with this route.  NIKHEF-H uses the service provider
   SURFNET (a service provider with customers with more than one routing

   policy), is also part of the High Energy Physics community as well as
   having the ability to access the Supercomputer at CERN (the community
   `CERN-SUPER', is somewhat national, but is intended as an example of
   a possible use of an access policy constraint).

   Example:

   route:     192.16.199.0/24
   descr:     Local Ethernet
   descr:     NIKHEF section H
   origin:    AS1104
   comm-list: HEPNET CERN-SUPER SURFNET
   changed:   ripe-dbm@ripe.net 920604
   source:    RIPE

   In the above examples some communities have been defined. The
   community object itself will take the following format:

   Example:

   community:  SURFNET
   descr:      Dutch academic research network
   authority:  SURFnet B.V.
   guardian:   comm-guardian@surfnet.nl
   admin-c:    Erik-Jan Bos
   tech-c:     Erik-Jan Bos
   changed:    ripe-dbm@ripe.net 920604
   source:     RIPE

   For a complete explanation of the syntax please refer to Appendix B.

9.  Representation of Routing Policies

   Routing policies of an AS are represented in the autonomous system
   object. Initially we show some examples, so the reader is familiar
   with the concept of how routing information is represented, used and
   derived. Refer to Appendix A, for the full syntax of the "aut-num"
   object.

   The topology of routing exchanges is represented by listing how
   routing information is exchanged with each neighboring AS.  This is
   done separately for both incoming and outgoing routing information.
   In order to provide backup and back door paths a relative cost is
   associated with incoming routing information.

   Example 1:

                               AS1------AS2

   This specifies a simple routing exchange of two presumably isolated
   ASes.  Even if either of them has routing information about routes in
   ASes other than AS1 and AS2, none of that will be announced to the
   other.

   aut-num:   AS1
   as-out:    to AS2 announce AS1
   as-in:     from AS2 100 accept AS2

   aut-num:   AS2
   as-out:    to AS1 announce AS2
   as-in:     from AS1 100 accept AS1

   The number 100 in the in-bound specifications is a relative cost,
   which is used for backup and back door routes. The absolute value is
   of no significance. The relation between different values within the
   same AS object is.  A lower value means a lower cost. This is
   consciously similar to the cost based preference scheme used with DNS
   MX RRs.

   Example 2:

   Now suppose that AS2 is connected to one more AS, besides AS1, and
   let's call that AS3:

                           AS1------AS2------AS3

   In this case there are two reasonable routing policies:

     a) AS2 just wants to exchange traffic with both AS1 and AS3 itself
        without passing traffic between AS1 and AS3.

     b) AS2 is willing to pass traffic between AS3 and AS1, thus acting
        as a transit AS

   Example 2a:

   In the first case AS1's representation in the routing registry will
   remain unchanged as will be the part of AS2's representation
   describing the routing exchange with AS1. A description of the
   additional routing exchange with AS3 will be added to AS2's
   representation:

   aut-num:   AS1
   as-out:    to AS2 announce AS1
   as-in:     from AS2 100 accept AS2

   aut-num:   AS2
   as-out:    to AS1 announce AS2
   as-in:     from AS1 100 accept AS1
   as-out:    to AS3 announce AS2
   as-in:     from AS3 100 accept AS3

   aut-num:   AS3
   as-out:    to AS2 announce AS3
   as-in:     from AS2 100 accept AS2

   Note that in this example, AS2 keeps full control over its resources.
   Even if AS3 and AS1 were to allow each others routes in from AS2, the
   routing information would not flow because AS2 is not announcing it.
   Of course AS1 and AS3 could just send traffic to each other to AS2
   even without AS2 announcing the routes, hoping that AS2 will forward
   it correctly. Such questionable practices however are beyond the
   scope of this document.

   Example 2b:

   If contrary to the previous case, AS1 and AS3 are supposed to have
   connectivity to each other via AS2, all AS objects have to change:

   aut-num:   AS1
   as-out:    to AS2 announce AS1
   as-in:     from AS2 100 accept AS2 AS3

   aut-num:   AS2
   as-out:    to AS1 announce AS2 AS3
   as-in:     from AS1 100 accept AS1
   as-out:    to AS3 announce AS2 AS1
   as-in:     from AS3 100 accept AS3

   aut-num:   AS3
   as-out:    to AS2 announce AS3
   as-in:     from AS2 100 accept AS1 AS2

   Note that the amount of routing information exchanged with a neighbor
   AS is defined in terms of routes belonging to ASes.  In BGP terms
   this is the AS where the routing information originates and the
   originating AS information carried in BGP could be used to implement
   the desired policy.  However, using BGP or the BGP AS-path
   information is not required to implement the policies thus specified.
   Configurations based on route lists can easily be generated from the
   database.  The AS path information, provided by BGP can then be used
   as an additional checking tool as desired.

   The specification understands one special expression and this can be
   expressed as a boolean expression:

   ANY - means any routing information known. For output this means that
        all routes an AS knows about are announced. For input it means
        that anything is accepted from the neighbor AS.

   Example 3:

   AS4 is a stub customer AS, which only talks to service provider
   AS123.

                                    |
                                    |
                            -----AS123------AS4
                                    |
                                    |

   aut-num: AS4
   as-out:  to AS123 announce AS4
   as-in:   from AS123 100 accept ANY

   aut-num: AS123
   as-in:   from AS4 100 accept AS4
   as-out:  to AS4 announce ANY
   <further neighbors>

   Since AS4 has no other way to reach the outside world than AS123 it
   is not strictly necessary for AS123 to send routing information to
   AS4.  AS4 can simply send all traffic for which it has no explicit
   routing information to AS123 by default.  This strategy is called
   default routing.  It is expressed in the routing registry by adding
   one or more default tags to the autonomous system which uses this
   strategy.  In the example above this would look like:

   aut-num: AS4
   as-out:  to AS123 announce AS4
   default: AS123 100

   aut-num: AS123
   as-in:   from AS4 100 accept AS4
   <further neighbors>

   Example 4:

   AS4 now connects to a different operator, AS5.  AS5 uses AS123 for
   outside connectivity but has itself no direct connection to AS123.
   AS5 traffic to and from AS123 thus has to pass AS4.  AS4 agrees to
   act as a transit AS for this traffic.

                              |
                              |
                       -----AS123------AS4-------AS5
                              |
                              |

   aut-num:    AS4
   as-out:     to AS123 announce AS4 AS5
   as-in:      from AS123 100 accept ANY
   as-out:     to AS5 announce ANY
   as-in:      from AS5 50 accept AS5

   aut-num:    AS5
   as-in:      from AS4 100 accept ANY
   as-out:     to AS4 announce AS5

   aut-num:    AS123
   as-in:      from AS4 100 accept AS4 AS5
   as-out:     to AS4 announce ANY
   <further neighbors>

   Now AS4 has two sources of external routing information. AS5 which
   provides only information about its own routes and AS123 which
   provides information about the external world. Note that AS4 accepts
   information about AS5 from both AS123 and AS5 although AS5
   information cannot come from AS123 since AS5 is connected only via
   AS4 itself. The lower cost of 50 for the announcement from AS5 itself
   compared to 100 from AS123 ensures that AS5 is still believed even in
   case AS123 will unexpectedly announce AS5.

   In this example too, default routing can be used by AS5 much like in
   the previous example.  AS4 can also use default routing towards
   AS123:

   aut-num:    AS4
   as-out:     to AS123 announce AS4 AS5
   default:    AS123 11
   as-in:      from AS5 50 accept AS5

   Note no announcements to AS5, they default to us.

   aut-num:    AS5
   as-out:     to AS4 announce AS5
   default:    AS4 100

   aut-num:    AS123
   as-in:      from AS4 100 announce AS4 AS5
   <further neighbors>

   Note that the relative cost associated with default routing is
   totally separate from the relative cost associated with in-bound
   announcements.  The default route will never be taken if an explicit
   route is known to the destination.  Thus an explicit route can never
   have a higher cost than the default route.  The relative cost
   associated with the default route is only useful in those cases where
   one wants to configure multiple default routes for redundancy.

   Note also that in this example the configuration using default routes
   has a subtly different behavior than the one with explicit routes: In
   case the AS4-AS5 link fails AS4 will send traffic to AS5 to AS123
   when using the default configuration. Normally this makes not much
   difference as there will be no answer and thus little traffic.  With
   certain datagram applications which do not require acknowledgments
   however, significant amounts of traffic may be uselessly directed at
   AS123.  Similarly default routing should not be used if there are
   stringent security policies which prescribe any traffic intended for
   AS5 to ever touch AS123.

   Once the situation gets more complex using default routes can lead to
   unexpected results or even defeat the routing policies established
   when links fail. As an example consider how Example 5a) below could
   be implemented using default routing.  Therefore, generally it can be
   said that default routing should only be used in very simple
   topologies.

   Example 5:

   In a different example AS4 has a private connection to AS6 which in
   turn is connected to the service provider AS123:

                                   |
                                   |
                            -----AS123------AS4
                                   |          |
                                   |          |
                                   |          |
                                 AS6 ---------+

   There are a number of policies worth examining in this case:

     a) AS4 and AS6 wish to exchange traffic between themselves
        exclusively via the private link between themselves; such
        traffic should never pass through the backbone (AS123).  The
        link should never be used for transit traffic, i.e. traffic not
        both originating in and destined for AS4 and AS6.

     b) AS4 and AS6 wish to exchange traffic between themselves via the
        private link between themselves.  Should the link fail, traffic
        between AS4 and AS6 should be routed via AS123.  The link should
        never be used for transit traffic.

     c) AS4 and AS6 wish to exchange traffic between themselves via the
        private link between themselves.  Should the link fail, traffic
        between AS4 and AS6 should be routed via AS123.  Should the
        connection between AS4 and AS123 fail, traffic from AS4 to
        destinations behind AS123 can pass through the private link and
        AS6's connection to AS123.

     d) AS4 and AS6 wish to exchange traffic between themselves via the
        private link between themselves.  Should the link fail, traffic
        between AS4 and AS6 should be routed via AS123.  Should the
        backbone connection of either AS4 or AS6 fail, the traffic of
        the disconnected AS should flow via the other AS's backbone
        connection.

   Example 5a:

   aut-num:   AS4
   as-in:     from AS123 100 accept NOT AS6
   as-out:    to AS123 announce AS4
   as-in:     from AS6 50 accept AS6
   as-out:    to AS6 announce AS4

   aut-num:   AS123
   as-in:     from AS4 100 accept AS4
   as-out:    to AS4 announce ANY
   as-in:     from AS6 100 accept AS6
   as-out:    to AS6 announce ANY
   <further neighbors>

   aut-num:    AS6
   as-in:      from AS123 100 accept NOT AS4
   as-out:     to AS123 announce AS6
   as-in:      from AS4 50 accept AS4
   as-out:     to AS4 announce AS6

   Note that here the configuration is slightly inconsistent. AS123 will
   announce AS6 to AS4 and AS4 to AS6. These announcements will be
   filtered out on the receiving end.  This will implement the desired
   policy.  Consistency checking tools might flag these cases however.

   Example 5b:

   aut-num:   AS4
   as-in:     from AS123 100 accept ANY
   as-out:    to AS123 announce AS4
   as-in:     from AS6 50 accept AS6
   as-out:    AS6 AS4

   aut-num:   AS123
   as-in:     AS4 100 AS4
   as-out:    AS4 ANY
   as-in:     AS6 100 AS6
   as-out:    AS6 ANY
   <further neighbors>

   aut-num:   AS6
   as-in:     from AS123 100 accept ANY
   as-out:    to AS123 announce AS6
   as-in:     from AS4 50 accept AS4
   as-out:    to AS4 announce AS6

   The thing to note here is that in the ideal operational case, `all
   links working' AS4 will receive announcements for AS6 from both AS123
   and AS6 itself.  In this case the announcement from AS6 will be
   preferred because of its lower cost and thus the private link will be
   used as desired.  AS6 is configured as a mirror image.

   Example 5c:

   The new feature here is that should the connection between AS4 and
   AS123 fail, traffic from AS4 to destinations behind AS123 can pass
   through the private link and AS6's connection to AS123.

   aut-num:  AS4
   as-in:    from AS123 100 accept ANY
   as-out:   to AS123 announce AS4
   as-in:    from AS6 50 accept AS6
   as-in:    from AS6 110 accept ANY
   as-out:   to AS6 AS4

   aut-num:  AS123
   as-in:    from AS4 1 accept AS4
   as-out:   to AS4 announce ANY
   as-in:    from AS6 1 accept AS6
   as-in:    from AS6 2 accept AS4
   as-out:   to AS6 announce ANY
   <further neighbors>

   aut-num:  AS6
   as-in:    from AS123 100 accept ANY
   as-out:   to AS123 AS6 announce AS4
   as-in:    from AS4 50 accept AS4
   as-out:   to AS4 announce ANY

   Note that it is important to make sure to propagate routing
   information for both directions in backup situations like this.
   Connectivity in just one direction is not useful at all for almost
   all applications.

   Note also that in case the AS6-AS123 connection breaks, AS6 will only
   be able to talk to AS4. The symmetrical case (5d) is left as an
   exercise to the reader.

10.  Future Extensions

   We envision that over time the requirements for describing routing
   policy will evolve. The routing protocols will evolve to support the
   requirements and the routing policy description syntax will need to
   evolve as well. For that purpose, a separate document will describe
   experimental syntax definitions for policy description.  This
   document [14] will be updated when new objects or attributes are
   proposed or modified.

11.  References

   [1]  Bates, T., Jouanigot, J-M., Karrenberg, D., Lothberg, P.,
        Terpstra, M., "Representation of IP Routing Policies in the RIPE
        Database", RIPE-81, February 1993.

   [2]  Merit Network Inc.,"Representation of Complex Routing Policies
        of an Autonomous System", Work in Progress, March 1994.

   [3]  PRIDE Tools Release 1.
        See ftp.ripe.net:pride/tools/pride-tools-1.tar.Z.

   [4]  Merit Inc. RRDB Tools.
        See rrdb.merit.edu:pub/meritrr/*

   [5]  The Network List Compiler.
        See dxcoms.cern.ch:pub/ripe-routing-wg/nlc-2.2d.tar

   [6]  Lord, A., Terpstra, M., "RIPE Database Template for Networks and
        Persons", RIPE-119, October 1994.

   [7]  Karrenberg, D., "RIPE Database Template for Domains", RIPE-49,
        April 1992.

   [8]  Lougheed, K., Rekhter, Y., "A Border Gateway Protocol 3 (BGP-
        3)", RFC1267, October 1991.

   [9]  Rekhter, Y., Li, T., "A Border Gateway Protocol 4 (BGP-4)",
        RFC-1654, May 1994.

   [10] Bates, T., Karrenberg, D., Terpstra, M., "Support for Classless
        Internet Addresses in the RIPE Database", RIPE-121, October
        1994.

   [11] Karrenberg, D., "Authorisation and Notification of Changes in
        the RIPE Database", RIPE-120, October 1994.

   [12] Bates, T., "Support of Guarded fields within the RIPE Database",
        ripe-117, July 1994.

   [13] Estrin, D., Li, T., Rekhter, Y., Varadhan, K., Zappala, D.,
        "Source Demand Routing: Packet Format and Forwarding
        Specification (Version 1)", Work in Progress, March 1994.

   [14] Joncheray, L., "Experimental Objects and attributes for the
        Routing Registry", RIPE-182, October1994.

   [15] Bates, T., "Specifying an `Internet Router' in the Routing

        Registry", RIPE-122, October 1994.

   [16] Bates, T., Karrenberg, D., Terpstra, M., "RIPE Database
        Transition Plan", RIPE-123, October 1994.

12.  Security Considerations

   Security issues are beyond the scope of this memo.

13.  Authors' Addresses

   Tony Bates
   MCI Telecommunications Corporation
   2100 Reston Parkway
   Reston, VA 22094
   USA
   +1 703 715 7521
   Tony.Bates@mci.net

   Elise Gerich
   The University of Michigan
   Merit Computer Network
   1075 Beal Avenue
   Ann Arbor, MI 48109
   USA
   +1 313 936 2120
   epg@merit.edu

   Laurent Joncheray
   The University of Michigan
   Merit Computer Network
   1075 Beal Avenue
   Ann Arbor, MI 48109
   USA
   +1 313 936 2065
   lpj@merit.edu

   Jean-Michel Jouanigot
   CERN, European Laboratory for Particle Physics
   CH-1211 Geneva 23
   Switzerland
   +41 22 767 4417
   Jean-Michel.Jouanigot@cern.ch

   Daniel Karrenberg
   RIPE Network Coordination Centre
   Kruislaan 409
   NL-1098 SJ Amsterdam
   The Netherlands
   +31 20 592 5065
   D.Karrenberg@ripe.net

   Marten Terpstra
   Bay Networks, Inc.
   2 Federal St
   Billerica, MA 01821
   USA
   +1 508 436 8036
   marten@BayNetworks.com

   Jessica Yu
   The University of Michigan
   Merit Computer Network
   1075 Beal Avenue
   Ann Arbor, MI 48109
   USA
   +1 313 936 2655
   jyy@merit.edu

Appendix A - Syntax for the aut-num object.

   Here is a summary of the tags associated with aut-num object itself
   and their status. The first column specifies the attribute, the
   second column whether this attribute is mandatory in the aut-num
   object, and the third column whether this specific attribute can
   occur only once per object [single], or more than once [multiple].
   When specifying multiple lines per attribute, the attribute name must
   be repeated. See [6] the example for the descr: attribute.

   aut-num:      [mandatory]          [single]
   as-name:      [optional]           [single]
   descr:        [mandatory]          [multiple]
   as-in:        [optional]           [multiple]
   as-out:       [optional]           [multiple]
   interas-in:   [optional]           [multiple]
   interas-out:  [optional]           [multiple]
   as-exclude:   [optional]           [multiple]
   default:      [optional]           [multiple]
   tech-c:       [mandatory]          [multiple]
   admin-c:      [mandatory]          [multiple]
   guardian:     [mandatory]          [single]
   remarks:      [optional]           [multiple]
   notify:       [optional]           [multiple]
   mnt-by:       [optional]           [multiple]
   changed:      [mandatory]          [multiple]
   source:       [mandatory]          [single]

   Each attribute has the following syntax:

   aut-num:
        The autonomous system number.  This must be a uniquely allocated
        autonomous system number from an AS registry (i.e. the RIPE NCC,
        the Inter-NIC, etc).

        Format:
             AS<positive integer between 1 and 65535>

        Example:

             aut-num: AS1104

        Status: mandatory, only one line allowed

as-name:
     The name associated with this AS. This should as short but as
     informative as possible.

     Format:
          Text consisting of capitals, dashes ("-") and digits, but must
          start with a capital.

     Example:

          as-name: NIKHEF-H

     Status: single, only one line allowed

descr:
     A short description of the Autonomous System.

     Format:
          free text

     Example:

          descr: NIKHEF section H
          descr: Science Park Watergraafsmeer
          descr: Amsterdam

     Status: mandatory, multiple lines allowed

as-in:
     A description of accepted routing information between AS peers.

     Format:
          from <aut-num> <cost> accept <routing policy expression>

          The keywords from and accept are optional and can be omitted.

          <aut-num> refers to your AS neighbor.

          <cost> is a positive integer used to express a relative cost
          of routes learned. The lower the cost the more preferred the
          route.

          <routing policy expression> can take the following formats.

          1.   A list of one or more ASes, AS Macros, Communities or
               Route Lists.

               A Route List is a list of routes in prefix length format,

               separated by commas, and surrounded by curly brackets
               (braces, i.e. `{' and '}').

               Examples:

                    as-in: from AS1103 100 accept AS1103
                    as-in: from AS786  105 accept AS1103
                    as-in: from AS786   10 accept AS786 HEPNET
                    as-in: from AS1755 110 accept AS1103 AS786
                    as-in: from AS3333 100 accept {192.87.45.0/16}

          2.   A set of KEYWORDS.  The following KEYWORD is currently
               defined:

               ANY  this means anything the neighbor AS knows.

          3.   A logical expression of either 1 or 2 above The current
               logical operators are defined as:

               AND
               OR
               NOT

               This operators are defined as true BOOLEAN operators even
               if the operands themselves do not appear to be BOOLEAN.
               Their operations are defined as follows:

               Operator       Operation      Example

                  OR          UNION          AS1 OR AS2
                                             |
                                             +-> all routes in AS1
                                                 or AS2.

                  AND         INTERSECTION   AS1 AND HEPNET
                                             |
                                             +-> a route in AS1 and
                                                 belonging to
                                                 community HEPNET.

                  NOT         COMPLEMENT     NOT AS3
                                             |
                                             +-> any route except
                                                 AS3 routes.

               Rules are grouped together using parenthesis i.e "(" and
               ")".

               The ordering of evaluation of operators and there
               association is as follows:

               Operator        Associativity

                  ()           left to right
                 NOT           right to left
                 AND           left to right
                  OR           left to right

               NOTE: if no logical operator is given between ASes, AS-
               macros, Communities, Route Lists and KEYWORDS it is
               implicitly evaluated as an `OR' operation.  The OR can be
               left out for conciseness. However, please note the
               operators are still evaluated as below so make sure you
               include parentheses whenever needed.  To highlight this
               here is a simple example. If we denoted a policy of for
               example; from AS1755 I accept all routes except routes
               from AS1, A2 and AS3 and you enter the following as-in
               line.

               as-in: from AS1755 100 accept NOT AS1 AS2 AS3

               This will be evaluated as:

               as-in: from AS1755 100 accept NOT AS1 OR AS2 OR AS3

               Which in turn would be evaluated like this:

               (NOT AS1) OR AS2 OR AS3
               -> ((ANY except AS1) union AS2) union AS3)
               --> (ANY except AS1)

               This is clearly incorrect and not the desired result. The
               correct syntax should be:

               as-in: from AS1755 100 accept NOT (AS1 AS2 AS3)

               Producing the following evaluation:

               NOT (AS1 OR AS2 OR AS3)
               -> (ANY) except (union of AS1, AS2, AS3)

               Which depicts the desired routing policy.
               Note that can also be written as below which is perhaps
               somewhat clearer:

               as-in: from AS1755 100 accept ANY AND NOT
               as-in: from AS1755 100 accept (AS1 OR AS2 OR AS3)

     Examples:

          as-in: from AS1755 100 accept ANY AND NOT (AS1234 OR AS513)
          as-in: from AS1755 150 accept AS1234 OR {35.0.0.0/8}

          A rule can be wrapped over lines providing the associated
          <aut-num>, <cost> values and from and accept keywords are
          repeated and occur on consecutive lines.

     Example:

          as-in: from AS1755 100 accept ANY AND NOT (AS1234 AS513)

             and

          as-in: from AS1755 100 accept ANY AND NOT (
          as-in: from AS1755 100 accept AS1234 AS513)

          are evaluated to the same result. Please note that the
          ordering of these continuing lines is significant.

     Status: optional, multiple lines allowed

as-out:
     A description of generated routing information sent to other AS
     peers.

     Format:
          to <aut-num> announce <routing policy expression

          The to and announce keywords are optional and can be omitted.

          <aut-num> refers to your AS neighbor.

          <routing policy expression> is explained in the as-in
          attribute definition above.

     Example:

          as-out: to AS1104 announce AS978
          as-out: to AS1755 announce ANY
          as-out: to AS786 announce ANY AND NOT (AS978)

     Status: optional, multiple lines allowed

interas-in:
     Describes incoming local preferences on an inter AS connection.

     Format:
          from <aut-num> <local-rid> <neighbor-rid> <preference> accept
          <routing policy expression>

          The keywords from and accept are optional and can be omitted.

          <aut-num> is an autonomous system as defined in as-in.

          <local-rid> contains the IP address of the border router in
          the AS describing the policy.  IP address must be in prefix
          length format.

          <neighbor-rid> contains the IP address of neighbor AS's border
          router from which this AS accept routes defined in the
          <routing policy expression>.  IP addresses must be in prefix
          length format.

          <preference> is defined as follows:

          (<pref-type>=<value>)

          It should be noted the parenthesis "(" and ")" and the
          "<pref-type>" keyword must be present for this preference to

          be valid.

          <pref-type> currently only supports "pref".  It could be
          expanded to other type of preference such as TOS/QOS as
          routing technology matures.

          <value> can take one of the following values:

          <cost>
               <cost> is a positive integer used to express a relative
               cost of routes learned. The lower the cost the more
               preferred the route. This <cost> value is only comparable
               to other interas-in attributes, not to as-in attributes.

          MED
               This indicates the AS will use the
               MUTLI_EXIT_DISCRIMINATOR (MED) metric, as implemented in
               BGP4 and IDRP, sent from its neighbor AS.

               NOTE: Combinations of MED and <cost> should be avoided
               for the same destinations.

               CAVEAT: The pref-type values may well be enhanced in the
               future as more inter-ASs routing protocols introduce
               other metrics.

               Any route specified in interas-in and not specified in
               as-in is assumed not accepted between the ASes concerned.
               Diagnostic tools should flag this inconsistency as an
               error.  It should be noted that if an interas-in policy
               is specified then it is mandatory to specify the
               corresponding global policy in the as-in line. Please
               note there is no relevance in the cost associated with
               as-in and the preferences used in interas-in.
          <routing policy expression> is an expression as defined in
          as-in above.

     Examples:

          NB: This line is wrapped for readability.
          interas-in: from AS1104 192.(pref=10)/accept.AS786.AS987
          interas-in: from AS1104 192.87.45.(pref=20)2accept.AS987
          interas-in: from AS1103 192.87.45.2(pref=MED)8accept2ANY

     Status: optional, multiple lines allowed

interas-out:

     Format:
          to <aut-num> <local-rid> <neighbor-rid> [<metric>] announce
          <routing policy expression>

          The keywords to and announce are optional and can be omitted.

          The definitions of <aut-num>, <local-rid> <neighbor-rid>, and
          <routing policy expression> are identical to those defined in
          interas-in.

          <metric> is optional and is defined as follows:

          (<metric-type>=<value>)

          It should be noted the parenthesis "(" and ")" and the
          keywords of "<metric-type>" must be present for this metric to
          be valid.

          <metric-type> currently only supports "metric-out".  It could
          be expanded to other type of preference such as TOS/QOS as
          routing technology matures.
          <value> can take one of the following values:

          <num-metric>
               <num-metric> is a pre-configured metric for out-bound
               routes. The lower the cost the more preferred the route.
               This <num-metric> value is literally passed by the
               routing protocol to the neighbor. It is expected that it
               is used there which is indicated by pref=MED on the
               corresponding interas-in attribute.  It should be noted
               that whether to accept the outgoing metric or not is
               totally within the discretion of the neighbor AS.

          IGP
               This indicates that the metric reflects the ASs internal
               topology cost. The topology is reflected here by using
               MED which is derived from the AS's IGP metric.

               NOTE: Combinations of IGP and <num-metric> should be
               avoided for the same destinations.

               CAVEAT: The metric-out values may well be enhanced in the
               future as more interas protocols make use of metrics.

               Any route specified in interas-out and not specified in
               as-out is assumed not announced between the ASes

               concerned. Diagnostic tools should flag this
               inconsistency as an error.  It should be noted that if an
               interas-out policy is specified then it is mandatory to
               specify the corresponding global policy in the as-out
               line.

     Examples:

          interas-out:ntoiAS1104p192.87.45.254/32t192.87.45.80/32
          interas-out: to AS1104m192.87.45.254/32n192.87.45.80/32
          interas-out: to AS1103 192.87.45.254/325192.87.45.80/32
                                    (metric-out=IGP) announce ANY

     Status: optional, multiple lines allowed

as-exclude:
     A list of transit ASes to ignore all routes from.

     Format:
          exclude <aut-num> to <exclude-route-keyword>

          Keywords exclude and to are optional and can again be omitted.

          <aut-num> refers to the transit AS in question.

          an <exclude-route-keyword> can be ONE of the following.

          1.   <aut-num>

          2.   AS macro

          3.   Community

          4.   ANY

     Examples:

          as-exclude: exclude AS690 to HEPNET

          This means exclude any HEPNET routes which have a route via
          AS690.

          as-exclude: exclude AS1800 to AS-EUNET

          This means exclude any AS-EUNET routes which have a route via
          AS1800.

          as-exclude: exclude AS1755 to AS1104

          This means exclude any AS1104 route which have a route via
          AS1755.

          as-exclude: exclude AS1104 to ANY

          This means exclude all routes which have a route via AS1104.

     Status: optional, multiple lines allowed

default:
     An indication of how default routing is done.

     Format:
          <aut-num> <relative cost> <default-expression>

          where <aut-num> is the AS peer you will default route to,

          and <relative cost> is the relative cost is a positive integer
          used to express a preference for default. There is no
          relationship to the cost used in the as-in tag. The AS peer
          with the lowest cost is used for default over ones with higher
          costs.

          <default-expression> is optional and provides information on
          how a default route is selected. It can take the following
          formats:

          1.   static. This indicates that a default is statically
               configured to this AS peer.

          2.   A route list with the syntax as described in the as-in
               attribute. This indicates that this list of routes is
               used to generate a default route. A special but valid
               value in this is the special route used by some routing
               protocols to indicate default: 0.0.0.0/0

          3.   default. This is the same as {0.0.0.0/0}. This means that
               the routing protocol between these two peers generates a
               true default.

     Examples:

          default: AS1755 10
          default: AS786   5 {140.222.0.0/16, 192.87.45.0/24}
          default: AS2043 15 default

     Status: optional, multiple lines allowed

tech-c:
     Full name or uniquely assigned NIC-handle of a technical contact
     person. This is someone to be contacted for technical problems such
     as misconfiguration.

     Format:
          <firstname> <initials> <lastname> or <nic-handle>

     Example:

          tech-c: John E Doe
          tech-c: JED31

     Status: mandatory, multiple lines allowed

admin-c:
     Full name or uniquely assigned NIC-handle of an administrative
     contact person. In many cases this would be the name of the
     guardian.

     Format:
          <firstname> <initials> <lastname>  or  <nic-handle>

     Example:

          admin-c: Joe T Bloggs
          admin-c: JTB1

     Status: mandatory, multiple lines allowed

guardian:
     Mailbox of the guardian of the Autonomous system.

     Format:
          <email-address>

          The <email-address> should be in RFC822 domain format wherever
          possible.

     Example:

          guardian: as1104-guardian@nikhef.nl

     Status: mandatory, only one line and e-mail address allowed

remarks:
     Remarks/comments, to be used only for clarification.

     Format:
          free text

     Example:

          remarks: Multihomed AS talking to AS1755 and AS786
          remarks: Will soon connect to AS1104 also.

     Status: optional, multiple lines allowed

notify:
     The notify attribute contains an email address to which
     notifications of changes to this object should be sent. See also
     [11].

     Format:
          <email-address>

          The <email-address> should be in RFC822 domain syntax wherever
          possible.

     Example:

          notify: Marten.Terpstra@ripe.net

     Status: optional, multiple lines allowed

mnt-by:
     The mnt-by attribute contains a registered maintainer name.  See
     also [11].

     Format:
          <registered maintainer name>

     Example:

          mnt-by: RIPE-DBM

     Status: optional, multiple lines allowed

changed:
     Who changed this object last, and when was this change made.

     Format:
          <email-address> YYMMDD

          <email-address> should be the address of the person who made
          the last change. YYMMDD denotes the date this change was made.

     Example:

          changed: johndoe@terabit-labs.nn 900401

     Status: mandatory, multiple lines allowed

source:
     Source of the information.

     This is used to separate information from different sources kept by
     the same database software. For RIPE database entries the value is
     fixed to RIPE.

     Format:
          RIPE
     Status: mandatory, only one line allowed

Appendix B - Syntax details for the community object.

   Here is a summary of the tags associated with community object itself
   and their status. The first column specifies the attribute, the
   second column whether this attribute is mandatory in the community
   object, and the third column whether this specific attribute can
   occur only once per object [single], or more than once [multiple].
   When specifying multiple lines per attribute, the attribute name must
   be repeated. See [6] the example for the descr: attribute.

   community:      [mandatory]          [single]
   descr:          [mandatory]          [multiple]
   authority:      [mandatory]          [single]
   guardian:       [mandatory]          [single]
   tech-c:         [mandatory]          [multiple]
   admin-c:        [mandatory]          [multiple]
   remarks:        [optional]           [multiple]
   notify:         [optional]           [multiple]
   mnt-by:         [optional]           [multiple]
   changed:        [mandatory]          [multiple]
   source:         [mandatory]          [single]

   Each attribute has the following syntax:

   community:
        Name of the community. The name of the community should be
        descriptive of the community it describes.

        Format:
             Upper case text string which cannot start with "AS" or any
             of the <routing policy expression> KEYWORDS. See Appendix
             A.

        Example:

             community: WCW

        Status: mandatory, only one line allowed

   descr:
        A short description of the community represented.

        Format:
             free text

        Example:

             descr: Science Park Watergraafsmeer
             descr: Amsterdam

        Status: mandatory, multiple lines allowed

   authority:
        The formal authority for this community. This could be an
        organisation, institute, committee, etc.

        Format:
             free text

        Example:

             authority:  WCW LAN Committee

        Status: mandatory, only one line allowed

   guardian:
        Mailbox of the guardian of the community.

        Format:
             <email-address>

             The <email-address> should be in RFC822 domain format
             wherever possible.

        Example:

             guardian: wcw-guardian@nikhef.nl

        Status: mandatory, only one line and email address allowed

   tech-c:
        Full name or uniquely assigned NIC-handle of an technical
        contact person for this community.

        Format:
             <firstname> <initials> <lastname> or <nic-handle>

        Example:

             tech-c: John E Doe
             tech-c: JED31

        Status: mandatory, multiple lines allowed

   admin-c:
        Full name or uniquely assigned NIC-handle of an administrative
        contact person. In many cases this would be the name of the
        guardian.

        Format:
             <firstname> <initials> <lastname> or <nic-handle>

        Example:

             admin-c: Joe T Bloggs
             admin-c: JTB1

        Status: mandatory, multiple lines allowed

   remarks:
        Remarks/comments, to be used only for clarification.

        Format:
             free text

        Example:

             remarks: Temporary community
             remarks: Will be removed after split into ASes

        Status: optional, multiple lines allowed

   notify:
        The notify attribute contains an email address to which
        notifications of changes to this object should be send. See also
        [11].

        Format:
             <email-address>

             The <email-address> should be in RFC822 domain syntax
             wherever possible.

        Example:

             notify: Marten.Terpstra@ripe.net

        Status: optional, multiple lines allowed

   mnt-by:
        The mnt-by attribute contains a registered maintainer name.  See
        also [11].

        Format:
             <registered maintainer name>

        Example:

             mnt-by: RIPE-DBM

        Status: optional, multiple lines allowed

   changed:
        Who changed this object last, and when was this change made.

        Format:
             <email-address> YYMMDD

             <email-address> should be the address of the person who
             made the last change. YYMMDD denotes the date this change
             was made.

        Example:

             changed: johndoe@terabit-labs.nn 900401

        Status: mandatory, multiple lines allowed

   source:
        Source of the information.

        This is used to separate information from different sources kept
        by the same database software. For RIPE database entries the
        value is fixed to RIPE.

        Format:
             RIPE
        Status: mandatory, only one line allowed

Appendix C - AS Macros syntax definition.

   Here is a summary of the tags associated with as-macro object itself
   and their status. The first column specifies the attribute, the
   second column whether this attribute is mandatory in the as-macro
   object, and the third column whether this specific attribute can
   occur only once per object [single], or more than once [multiple].
   When specifying multiple lines per attribute, the attribute name must
   be repeated. See [6] the example for the descr: attribute.

   as-macro:     [mandatory]          [single]
   descr:        [mandatory]          [multiple]
   as-list:      [mandatory]          [multiple]
   guardian:     [mandatory]          [single]
   tech-c:       [mandatory]          [multiple]
   admin-c:      [mandatory]          [multiple]
   remarks:      [optional]           [multiple]
   notify:       [optional]           [multiple]
   mnt-by:       [optional]           [multiple]
   changed:      [mandatory]          [multiple]
   source:       [mandatory]          [single]

   Each attribute has the following syntax:

   as-macro:
        The name of a macro containing at least two Autonomous Systems
        grouped together for ease of administration.

        Format:
             AS-<string>

             The <string> should be in upper case and not contain any
             special characters.

        Example:

             as-macro: AS-EBONE

        Status: mandatory, only one line allowed

   descr:
        A short description of the Autonomous System Macro.

        Format:
             free text

        Example:

             descr:  Macro for EBONE connected ASes

        Status: mandatory, multiple lines allowed

   as-list:
        The list of ASes or other AS macros that make up this macro. It
        should be noted that recursive use of AS macros is to be
        encouraged.

        Format:
             <aut-num> <as-macro> ...

             See Appendix A for <aut-num> definition.

        Example:

             as-list: AS786 AS513 AS1104
             as-list: AS99 AS-NORDUNET

        Status: mandatory, multiple lines allowed

   guardian:
        Mailbox of the guardian of this AS macro.

        Format:
             <email-address>

             The <email-address> should be in RFC822 domain format
             wherever possible.

        Example:

             guardian: as-ebone-guardian@ebone.net

        Status: mandatory, only one line and e-mail address allowed

   tech-c:
        Full name or uniquely assigned NIC-handle of a technical contact
        person for this macro. This is someone to be contacted for
        technical problems such as misconfiguration.

        Format:
             <firstname> <initials> <lastname> or <nic-handle>

        Examples:

             tech-c: John E Doe
             tech-c: JED31

        Status: mandatory, multiple lines allowed

   admin-c:
        Full name or uniquely assigned NIC-handle of an administrative
        contact person. In many cases this would be the name of the
        guardian.

        Format:
             <firstname> <initials> <lastname> or <nic-handle>

        Examples:

             admin-c: Joe T Bloggs
             admin-c: JTB1

        Status: mandatory, multiple lines allowed

   remarks:
        Remarks/comments, to be used only for clarification.

        Format:
             free text

        Example:

             remarks: AS321 will be removed from this Macro shortly

        Status: optional, multiple lines allowed

   notify:
        The notify attribute contains an email address to which
        notifications of changes to this object should be send. See also
        [11].

        Format:
             <email-address>

             The <email-address> should be in RFC822 domain syntax
             wherever possible.

        Example:

             notify: Marten.Terpstra@ripe.net

        Status: optional, multiple lines allowed

   mnt-by:
        The mnt-by attribute contains a registered maintainer name.  See
        also [11].

        Format:
             <registered maintainer name>

        Example:

             mnt-by: RIPE-DBM

        Status: optional, multiple lines allowed

   changed:
        Who changed this object last, and when was this change made.

        Format:
             <email-address> YYMMDD

             <email-address> should be the address of the person who
             made the last change. YYMMDD denotes the date this change
             was made.

        Example:

             changed: johndoe@terabit-labs.nn 900401

        Status: mandatory, multiple lines allowed

   source:
        Source of the information.

        This is used to separate information from different sources kept
        by the same database software. For RIPE database entries the
        value is fixed to RIPE.

        Format:
             RIPE
        Status: mandatory, only one line allowed

Appendix D - Syntax for the "route" object.

   There is a summary of the tags associated with route object itself
   and their status. The first column specifies the attribute, the
   second column whether this attribute is mandatory in the community
   object, and the third column whether this specific attribute can
   occur only once per object [single], or more than once [multiple].
   When specifying multiple lines per attribute, the attribute name must
   be repeated. See [6] the example for the descr: attribute.

   route:          [mandatory]          [single]
   descr:          [mandatory]          [multiple]
   origin:         [mandatory]          [single]
   hole:           [optional]           [multiple]
   withdrawn:      [optional]           [single]
   comm-list:      [optional]           [multiple]
   remarks:        [optional]           [multiple]
   notify:         [optional]           [multiple]
   mnt-by:         [optional]           [multiple]
   changed:        [mandatory]          [multiple]
   source:         [mandatory]          [single]

   Each attribute has the following syntax:

   route:
        Route being announced.

        Format:
             Classless representation of a route with the RIPE database
             known as the "prefix length" representation. See [10] for
             more details on classless representations.

        Examples:

             route: 192.87.45.0/24

             This represents addressable bits 192.87.45.0 to
             192.87.45.255.

             route: 192.1.128.0/17

             This represents addressable bits 192.1.128.0 to
             192.1.255.255.

        Status: mandatory, only one line allowed

   origin:
        The autonomous system announcing this route.

        Format:
             <aut-num>

             See Appendix A for <aut-num> syntax.

        Example:

             origin: AS1104

        Status: mandatory, only one line allowed

   hole:
        Denote the parts of the address space covered this route object
        to which the originator does not provide connectivity. These
        holes may include routes that are being currently routed by
        another provider (e.g., a customer using that space has moved to
        a different service provider).  They may also include space that
        has not yet been assigned to any customer.

        Format:
             Classless representation of a route with the RIPE database
             known as the "prefix length" representation. See [10] for
             more details on classless representations. It should be
             noted that this sub-aggregate must be a component of that
             registered in the route object.

        Example:

             hole: 193.0.4.0/24

        Status: optional, multiple lines allowed

   withdrawn:
        Used to denote the day this route has been withdrawn from the
        Internet routing mesh. This will be usually be used when a less
        specific aggregate route is now routed the more specific (i.e.
        this route) is not need anymore.

        Format:
             YYMMDD

             YYMMDD denotes the date this route was withdrawn.

        Example:

             withdrawn: 940711

        Status: optional, one line allowed.

   comm-list:
        List of one or more communities this route is part of.

        Format:
             <community> <community> ...

             See Appendix B for <community> definition.

        Example:

             comm-list: HEP LEP

        Status: optional, multiple lines allowed

   remarks:
        Remarks/comments, to be used only for clarification.

        Format:
             free text

        Example:

             remarks: Multihomed AS talking to AS1755 and AS786
             remarks: Will soon connect to AS1104 also.

        Status: optional, multiple lines allowed

   notify:
        The notify attribute contains an email address to which
        notifications of changes to this object should be send. See also
        [11].

        Format:
             <email-address>

             The <email-address> should be in RFC822 domain syntax
             wherever possible.

        Example:

             notify: Marten.Terpstra@ripe.net

        Status: optional, multiple lines allowed

   mnt-by:
        The mnt-by attribute contains a registered maintainer name.  See
        also [11].

        Format:
             <registered maintainer name>

        Example:

             mnt-by: RIPE-DBM

        Status: optional, multiple lines allowed

   changed:
        Who changed this object last, and when was this change made.

        Format:
             <email-address> YYMMDD

             <email-address> should be the address of the person who
             made the last change. YYMMDD denotes the date this change
             was made.

        Example:

             changed: johndoe@terabit-labs.nn 900401

        Status: mandatory, multiple lines allowed

   source:
        Source of the information.

        This is used to separate information from different sources kept
        by the same database software. For RIPE database entries the
        value is fixed to RIPE.

        Format:
             RIPE
        Status: mandatory, only one line allowed

Appendix E - List of reserved words

   The following list of words are reserved for use within the
   attributes of the AS object. The use of these words is solely for the
   purpose of clarity. All keywords must be lower case.

           accept
           announce
           exclude
           from
           to
           transit

   Examples of the usage of the reserved words are:

   as-in: from <neighborAS> accept <route>

   as-out: to <neighborAS> announce <route>

   as-exclude: exclude <ASpath> to <destination>

   as-transit: transit <ASpath> to <destination>

   default: from <neighborAS> accept <route>

   default: to <neighborAS> announce <route>

   Note: that as-transit is an experimental attribute. See section 10.

Appendix F - Motivations for RIPE-81++

   This appendix gives motivations for the major changes in this
   proposal from ripe-81.

   The main goals of the routing registry rework are:

     SPLIT
        Separate the allocation and routing registry functions into
        different database objects. This will facilitate data management
        if the Internet registry and routing registry functions are
        separated (like in other parts of the world). It will also make
        more clear what is part of the routing registry and who has
        authority to change allocation vs. routing data.

      CIDR
        Add the possibility to specify classless routes in the routing
        registry.  Classless routes are being used in Internet
        production now.  Aggregation information in the routing registry
        is necessary for network layer troubleshooting. It is also
        necessary because aggregation influences routing policies
        directly.

     CALLOC
        Add the possibility to allocate address space on classless
        boundaries in the allocation registry. This is a way to preserve
        address space.

     CLEAN
        To clean up some of the obsolete and unused parts of the routing
        registry.

   The major changes are now discussed in turn:

   Introduce Classless Addresses

   CIDR, CALLOC

   Introduce route object.

   SPLIT, CIDR and CALLOC.

   Delete obsolete attributes from inetnum.

   CLEAN.

   Delete RIPE-DB and LOCAL from routing policy expressions.

   CLEAN

   Allow multiple ASes to originate the same route

   Because it is being done. CIDR. Made possible by SPLIT.

Appendix G - Transition strategy from RIPE-81 to RIPE-81++

Transition from the routing registry described by ripe-81 to the routing
registry described in this document is a straightforward process once
the new registry functions have been implemented in the database
software and are understood by the most commonly used registry tools.
The routing related attributes in the classful inetnum objects of ripe-
81 can be directly translated into new routing objects. Then these
attributes can be deleted from the inetnum object making that object if
conform to the new schema.

Proposed transition steps:

  1) Implement classless addresses and new object definition in the
     database software.

  2) Make common tools understand the new schema and prefer it if both
     old and new are present.

  3) Invite everyone to convert their data to the new format.  This can
     be encouraged by doing conversions automatically and proposing them
     to maintainers.

  4) At a flag day remove all remaining routing information from the
     inetnum objects.  Before the flag day all usage of obsoleted
     inetnum attributes has to cease and all other routing registry
     functions have to be taken over by the new objects and attributes.

 

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