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RFC 2835 - IP and ARP over HIPPI-6400 (GSN)


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Network Working Group                                        J.-M. Pittet
Request for Comments: 2835                          Silicon Graphics Inc.
Category: Standards Track                                        May 2000

                    IP and ARP over HIPPI-6400 (GSN)

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2000).  All Rights Reserved.

Abstract

   The ANSI T11.1 task force has standardized HIPPI-6400 also known as
   Gigabyte System Network (GSN), a physical-level, point-to-point,
   full-duplex, link interface for reliable, flow-controlled,
   transmission of user data at 6400 Mbit/s, per direction. A parallel
   copper cable interface for distances of up to 40 m is specified in
   HIPPI-6400-PH [1].  Connections to a longer-distance optical
   interface are standardized in HIPPI-6400-OPT [3].

   HIPPI-6400-PH [1] defines the encapsulation of IEEE 802.2 LLC PDUs
   [10] and by implication, IP on GSN. Another T11.1 standard describes
   the operation of HIPPI-6400 physical switches HIPPI-6400-SC [2].
   T11.1 chose to leave HIPPI-6400 networking issues largely outside the
   scope of their standards; this document specifies the use of HIPPI-
   6400 switches as IP local area networks. This document further
   specifies a method for resolving IP addresses to HIPPI-6400 hardware
   addresses (HARP) and for emulating IP broadcast in a logical IP
   subnet (LIS) as a direct extension of HARP. Furthermore it is the
   goal of this memo to define a IP and HARP that will allow
   interoperability for HIPPI-800 and HIPPI-6400 equipment both
   broadcast and non-broadcast capable networks.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Definitions . . . . . . . . . . . . . . . . . . . . . . .   3
       2.1 Global concepts used  . . . . . . . . . . . . . . . .   3
       2.2 Glossary  . . . . . . . . . . . . . . . . . . . . . .   4

   3.  IP Subnetwork Configuration . . . . . . . . . . . . . . .   5
       3.1 Background  . . . . . . . . . . . . . . . . . . . . .   5
       3.2 HIPPI LIS Requirements  . . . . . . . . . . . . . . .   6
   4.  Internet Protocol . . . . . . . . . . . . . . . . . . . .   7
       4.1  Packet Format  . . . . . . . . . . . . . . . . . . .   7
            4.1.1 IEEE 802.2 LLC . . . . . . . . . . . . . . . .   7
            4.1.2 SNAP . . . . . . . . . . . . . . . . . . . . .   7
            4.1.3 Packet diagrams  . . . . . . . . . . . . . . .   8
       4.2  HIPPI-6400 Hardware address: Universal LAN MAC addr.   9
       4.3  Maximum Transmission Unit - MTU  . . . . . . . . . .  10
   5.  HIPPI Address Resolution Protocol - HARP  . . . . . . . .  11
       5.1  HARP Algorithm . . . . . . . . . . . . . . . . . . .  12
            5.1.1 Selecting the authoritative HARP service . . .  12
            5.1.2 HARP registration phase  . . . . . . . . . . .  13
            5.1.3 HARP operational phase . . . . . . . . . . . .  14
       5.2  HARP Client Operational Requirements . . . . . . . .  15
       5.3  Receiving Unknown HARP Messages  . . . . . . . . . .  16
       5.4  HARP Server Operational Requirements . . . . . . . .  16
       5.5  HARP and Permanent ARP Table Entries . . . . . . . .  18
       5.6  HARP Table Aging . . . . . . . . . . . . . . . . . .  18
   6.  HARP Message Encoding . . . . . . . . . . . . . . . . . .  19
       6.1 Generic IEEE 802 ARP Message Format . . . . . . . . .  19
       6.2 HIPARP Message Formats  . . . . . . . . . . . . . . .  21
           6.2.1 Example Message encodings:  . . . . . . . . . .  23
           6.2.2 HARP_NAK message format . . . . . . . . . . . .  24
   7.  Broadcast and Multicast   . . . . . . . . . . . . . . . .  24
       7.1 Protocol for an IP Broadcast Emulation Server - PIBES  25
       7.2 IP Broadcast Address  . . . . . . . . . . . . . . . .  25
       7.3 IP Multicast Address  . . . . . . . . . . . . . . . .  25
       7.4 A Note on Broadcast Emulation Performance . . . . . .  26
   8.  HARP for Scheduled Transfer . . . . . . . . . . . . . . .  26
   9.  Security Consierations  . . . . . . . . . . . . . . . . .  26
   10. Open Issues . . . . . . . . . . . . . . . . . . . . . . .  27
   11.  HARP Examples  . . . . . . . . . . . . . . . . . . . . .  27
        11.1 Registr. Phase of Client Y on Non-broadcast Hardware 27
        11.2 Registr. Phase of Client Y on Broadcast-capable . .  28
        11.3 Operational Phase (phase II)  . . . . . . . . . . .  29
             11.3.1 Successful HARP_Resolve example  . . . . . .  29
             11.3.2 Non-successful HARP_Resolve example  . . . .  30
   12.  References . . . . . . . . . . . . . . . . . . . . . . .  31
   13.  Acknowledgments  . . . . . . . . . . . . . . . . . . . .  32
   14.  Author's Address . . . . . . . . . . . . . . . . . . . .  32
   15.  Full Copyright Statement . . . . . . . . . . . . . . . .  33

1. Introduction

   HIPPI-6400 is a duplex data channel that can transmit and receive
   data simultaneously at nearly 6400 megabits per second. HIPPI-6400
   data transfers are segmented into micropackets, each composed of 32
   data bytes and 8 control bytes. HIPPI-6400 uses four multiplexed
   virtual channels. These virtual channels are allocated to control
   traffic, low latency traffic, and bulk traffic (see [1] for more
   details).

   Using small packets and four virtual channels, large file transfers
   cannot lock out a host or switch port for interactive traffic.
   HIPPI-6400 guarantees in order delivery of data. It also supports
   link-level and end-to-end checksumming and credit-based flow control.

   HIPPI-6400-PH defines a 20-bit interface for copper cables operating
   at 500 MBaud. This provides a user payload bandwidth of 6400 Mb/s
   (800,000,000 Bytes/sec) in each direction. [8]

   HIPPI-6400-SC [2] defines two types of switches: bridging and non-
   bridging. The bridging switches are required to support hardware
   broadcast.  Non-bridging switches are not required to support
   broadcast.  This memo allows for a coherent implementation of IP and
   HARP with both types of switches.

   Gigabyte System Network(TM) (GSN) is a marketing name for HIPPI-6400.
   It is a trademark of the High Performance Networking Forum (HNF;
   http://www.hnf.org) for use by its member companies that supply
   products complying to ANSI HIPPI-6400 standards.

2  Definitions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC-2119 [19].

2.1 Global concepts used

   In the following discussion, the terms "requester" and "target" are
   used to identify the port initiating the address resolution request
   and the port whose address it wishes to discover, respectively. This
   document will use HIPPI-800 and HIPPI-6400 when referring to concepts
   that apply to one or the other technology. The term HIPPI will be
   used when referring to both technologies.

   Values are decimal unless otherwise noted. Formatting follows IEEE
   802.1A canonical bit order and HIPPI-6400-PH bit and byte ordering.

2.2 Glossary

   Broadcast

   A distribution mode which transmits a message to all ports. The
   sending port is part of "all" and will therefore also receive a copy
   of the sent message.

   Classical/Conventional

   Both terms are used with respect to networks, including Ethernet,
   FDDI, and other 802 LAN types, as distinct from HIPPI-SC LANs.

   Destination

   The HIPPI port that receives data from a HIPPI Source.

   HARP

   HARP (HIPPI Address Resolution Protocol describes the whole set of
   HIPPI-6400 address resolution encodings and algorithms defined in
   this memo. HARP is a combination and adaptation of the Internet
   Address Resolution Protocol (ARP) RFC-826 [14] and Inverse ARP
   (InARP) [5] (see section 5). HARP also describes the HIPPI (800 and
   6400) specific version of ARP (i.e. the protocol and the HIPPI
   specific encoding).

   HARP table

   Each host has a HARP table which contains the IP to hardware address
   mapping of IP members.

   HRAL

   The HARP Request Address List.  A list of ULAs to which HARP messages
   are sent when resolving names to addresses (see section 3.2).

   Hardware (HW) address

   The hardware address of a port; it consists of an ULA (see section
   4.2). Note: the term port as used in this document refers to a HIPPI
   port and is roughly equivalent to the term "interface" as commonly
   used in other IP documents.

   Host

   An entity, usually a computer system, that may have one or more HIPPI
   ports and which may serve as a client or a HARP server.

   Port

   An entity consisting of one HIPPI Source/Destination dual simplex
   pair that is connected by parallel or serial HIPPI to a HIPPI-SC
   switch and that transmits and receives IP datagrams.  A port may be
   an Internet host, bridge, router, or gateway.

   PIBES

   The Protocol for Internet Broadcast Emulation Server (see section 7).

   Source

   The HIPPI port that generates data to send to a HIPPI Destination.

   Universal LAN MAC Address (ULA)

   A 48-bit globally unique address, administered by the IEEE, assigned
   to each port on an Ethernet, FDDI, 802 network, or HIPPI-SC LAN.

3.  IP Subnetwork Configuration

3.1 Background

   ARP (address resolution protocol) as defined in [14] was meant to
   work on the 'local' cable. This definition gives the ARP protocol a
   local logical IP subnet (LIS) scope. In the LIS scenario, each
   separate administrative entity configures its hosts and routers
   within the LIS. Each LIS operates and communicates independently of
   other LIS's on the same HIPPI-6400 network.

   HARP has LIS scope only and serves all ports in the LIS.
   Communication to ports located outside of the local LIS is usually
   provided via an IP router. This router is a HIPPI-6400 port attached
   to the HIPPI-6400 network that is configured as a member of one or
   more LIS's. This configuration MAY result in a number of disjoint
   LIS's operating over the same HIPPI-6400 network. Using this model,
   ports of different IP subnets SHOULD communicate via an intermediate
   IP router even though it may be possible to open a direct HIPPI-6400
   connection between the two IP members over the HIPPI-6400 network.
   This is an consequence of using IP and choosing to have multiple
   LIS's on the same HIPPI-6400 fabric.

   By default, the HARP method detailed in section 5 and the classical
   LIS routing model MUST be available to any IP member client in the
   LIS.

3.2 HIPPI LIS Requirements

   The requirement for IP members (hosts, routers) operating in a
   HIPPI-6400 LIS configuration is:

   o  All members of the LIS SHALL have the same IP network/subnet
      address and address mask [4].

   The following list identifies the set of HIPPI-6400-specific
   parameters that MUST be implemented in each IP station connected to
   the HIPPI-6400 network:

   o  HIPPI-6400 Hardware Address:

      The HIPPI-6400 hardware address (a ULA) of an individual IP
      endpoint (i.e. a network adapter within a host) MUST be unique in
      the LIS.

   o  HARP Request Address List (HRAL):

   The HRAL is an ordered list of two or more addresses identifying the
   address resolution service(s).  All HARP clients MUST be configured
   identically, i.e. all ports MUST have the same addresses(es) in the
   HRAL.

   The HRAL MUST contain at least two HIPPI HW addresses identifying the
   individual HARP service(s) that have authoritative responsibility for
   resolving HARP requests of all IP members located within the LIS.  By
   default the first address MUST be the reserved address for broadcast,
   i.e. FF:FF:FF:FF:FF:FF.

   The second address MUST be the standard HW address for the HARP
   server 00:10:3B:FF:FF:E0.

   Therefore, the HRAL entries are sorted in the following order:
   1st     : broadcast address            (FF:FF:FF:FF:FF:FF) REQUIRED
   2nd     : official HARP server address (00:10:3B:FF:FF:E0) REQUIRED
   3rd & on: any additional HARP server addresses will be     OPTIONAL
             sorted in decreasing order.

   Manual configuration of the addresses and address lists presented in
   this section is implementation dependent and beyond the scope of this
   memo.  However, prior to use by any service or operation detailed in
   this memo, clients MUST have HRAL address(es) configured as
   appropriate for their LIS.

4.  Internet Protocol

4.1 Packet format

   The HIPPI-6400 packet format for Internet datagrams [15] shall
   conform to the HIPPI-6400-PH standard [1].  The length of a HIPPI-
   6400-PH packet, including headers and trailing fill, shall be a
   multiple of 32 bytes as required by HIPPI-6400-PH.

   All IP Datagrams shall be carried on HIPPI-6400-PH Virtual Channel 1
   (VC1). Since HIPPI-6400-PH has a 32-byte granularity, IP Datagrams
   MUST be padded to a 32-byte granularity prior to sending. Added
   padding is transparent to IP and is not reflected in the length field
   of the IP header.

   D_ULA   Destination ULA SHALL be the ULA of the destination port.

   S_ULA   Source ULA SHALL be the ULA of the requesting port.

   M_len   Set to the IEEE 802 packet (e.g. IP or HARP message)
           length + 8 Bytes to account for the LLC/SNAP header length.
           The HIPPI-6400-PH [1] length parameter shall not include
           the pad.

4.1.1 IEEE 802.2 LLC

   The IEEE 802.2 LLC Header SHALL begin in the first byte after M_len.

   The LLC values (in hexadecimal and decimal) SHALL be

   SSAP           0xAA     170  (8  bits)
   DSAP           0xAA     170  (8  bits)
   CTL            0x03       3  (8  bits)

   for a total length of 3 bytes. The 0x03 CTL value indicates the
   presence of a SNAP header.

4.1.2 SNAP

   The OUI value for Organization Code SHALL be 0x00-00-00 (3 bytes)
   indicating that the following two-bytes is an Ethertype.

   The Ethertype value SHALL be set as defined in Assigned Numbers [18]:

   IP           0x0800  2048  (16 bits)
   HARP = ARP = 0x0806  2054  (16 bits)

   The total size of the LLC/SNAP header is fixed at 8 bytes.

4.1.3 HIPPI-6400 802 Packet diagrams

   The following diagram shows a HIPPI-6400 message carrying IEEE 802
   data.

   |31          |23          |15          |7          0|
   +------------+------------+------------+------------+ -------------
 0 |                                                   |
   |         D_ULA           +-------------------------+   HIPPI-6400
 1 |                         |                         |
   +-------------------------+        S_ULA            |      MAC
 2 |                                                   |
   +---------------------------------------------------+     header
 3 |                      M_len                        |
   +------------+------------+------------+------------+ -------------
 4 |   DSAP     |   SSAP     |    Ctl     |    Org     |    IEEE 802
   +------------+------------+------------+------------+    LLC/SNAP
 5 |   Org      |    Org     |       Ethertype         |     header
   +============+============+============+============+ =============
 6 | Msg byte 0 | Msg byte 1 | Msg byte 2 |    . . .   |    IEEE 802
   +---------------------------------------------------+      Data
                   Generic 802.1 data packet diagram

   The following diagram shows an IP datagram of length n with the FILL
   bytes ( value: 0x0 ). "<><>" indicates the micropacket separation. A
   HIPPI-6400-PH [1] micropacket is 32 bytes long.

   All IP (v4) [15] packets will always span two or more micropackets.
   The first micropacket has a TYPE = header. The second and any further
   micropackets have a TYPE = Data (see [1]).

    |31          |23          |15          |7          0|
    +------------+------------+------------+------------+ -------------
  0 |                                                   |
    |         D_ULA           +-------------------------+   HIPPI-6400
  1 |                         |                         |
    +-------------------------+        S_ULA            |      MAC
  2 |                                                   |
    +---------------------------------------------------+     header
  3 |                      M_len                        |
    +------------+------------+------------+------------+ -------------
  4 |     AA     |     AA     |     03     |    00      |    IEEE 802
    +------------+------------+------------+------------+    LLC/SNAP
  5 |     00     |     00     | Ethertype = 0x0800=2048 |     header
    +============+============+============+============+ =============
  6 | VER | HLEN |    TOS     |      Total Length       |
    +-----+------+------------+-----+-------------------+
  7 |           ID            | FLG |   Frag Offset     |
    +<><><><><><>+<><><><><><>+<><><><><><>+<><><><><><>+  IPv4 Header
  8 |    TTL     |   PROTO    |    Header Checksum      |
    +------------+------------+-------------------------+
  9 |                 Source IP Address                 |
    +---------------------------------------------------+
 10 |               Destination IP Address              |
    +---------------------------------------------------+
 11 |                    .   .   .                      |
    +---------------------------------------------------+
    |   . . .    | byte (n-2) | byte (n-1) |    FILL    |
    +------------+------------+------------+------------+
    |    FILL    |   FILL     |   FILL     |    FILL    |
    +------------+------------+------------+------------+
 M-1|    FILL    |   FILL     |   FILL     |    FILL    |
    +<><><><><><>+<><><><><><>+<><><><><><>+<><><><><><>+
                       IP v4 data packet diagram

   As shown in above figure the first eight bytes of the IP Datagram
   occupy the last eight bytes of the HIPPI-6400-PH [1] Header
   micropacket.

4.2  HIPPI-6400 Hardware address: Universal LAN MAC address (ULA)

   HIPPI-6400 uses Universal LAN MAC Addresses specified in IEEE
   Standard 802.1A [10] or a subset as defined in HIPPI-6400-SC [2].
   The globally unique part of the 48 bit space is administered by the
   IEEE. Each port on a HIPPI-6400-SC LAN MUST be assigned a ULA.
   Multiple ULAs may be used if a node contains more than one IEEE 802.2
   LLC protocol entity.

   This memo assumes the use of "Logical Addressing" as described in
   Annex A.2 of HIPPI-6400-SC[2].

   The format of the address within its 48 bit HIPPI-6400-PH fields
   follows IEEE 802.1A canonical bit order and HIPPI-6400-PH bit and
   byte order:

    31              23              15               7              0
   +---------------+---------------+---------------+---------------+
   |ULA byte 0 |L|G|   ULA byte 1  |   ULA byte 2  |   ULA byte 3  |
   +---------------+---------------+---------------+---------------+
   |   ULA byte 4  |   ULA byte 5  |      (not used for ULA)       |
   +---------------+---------------+---------------+---------------+

                     Universal LAN MAC Address Format

   L (U/L bit) = 1 for Locally administered addresses, 0 for Universal.
   G (I/G bit) = 1 for Group addresses, 0 for Individual.

4.3  Maximum Transmission Unit - MTU

   Maximum Transmission Unit (MTU) is defined as the maximum length of
   the IP packet, including IP header, but not including any overhead
   below IP, i.e., HIPPI-6400 MAC header and IEEE 802 LLC/SNAP header.
   Conventional LANs have MTU sizes determined by physical layer
   specification.  MTUs may be required simply because the chosen medium
   won't work with larger packets, or they may serve to limit the amount
   of time a node must wait for an opportunity to send a packet.

   HIPPI-6400-PH [1] limits packets to about 4 gigabytes (on VC 3) which
   imposes no practical limit for networking purposes. HIPPI-6400-PH VC
   1, which was chosen for IP and ARP traffic, limits messages to about
   128 Kbytes which is still larger than the HIPPI-800 MTU [17].

   The MTU for HIPPI-6400 LANs SHALL be 65280 (decimal) bytes.

   This value is backwards compatible with HIPPI-800. It allows the IP
   packet to fit in one 64K byte buffer with up to 256 bytes of
   overhead.  The IP v4 overhead is 24 bytes for HIPPI-6400 and 40 bytes
   for HIPPI-800.

   For HIPPI-6400 the byte accounting is:

      HIPPI-6400-PH Header            16 bytes
      IEEE 802.2 LLC/SNAP Headers      8 bytes
      Maximum IP packet size (MTU) 65280 bytes
      Unused expansion room          232 bytes
                                   ------------
                        Total      65536 bytes (64K)

   In contrast, the HIPPI-800 accounting is:

      HIPPI-800-FP Header              8 bytes
      HIPPI-800-LE Header             24 bytes
      IEEE 802.2 LLC/SNAP Headers      8 bytes
      Unused expansion room          216 bytes
      Maximum IP packet size (MTU) 65280 bytes
                                   ------------
                        Total      65536 bytes (64K)

5. HIPPI Address Resolution Protocol - HARP

   Address resolution within the HIPPI-6400 LIS SHALL make use of the
   HIPPI Address Resolution Protocol (HARP) and the Inverse HIPPI
   Address Resolution Protocol (InHARP). HARP provides the same
   functionality as the Internet Address Resolution Protocol (ARP).

   HARP is based on ARP which is defined in RFC-826 [14] except the
   HIPPI-6400 specific packet format. Knowing the Internet address,
   conventional networks use ARP to discover another node's hardware
   address.  HARP presented in this section further specifies the
   combination of the original protocol definitions to form a coherent
   address resolution service that is independent of the hardware's
   broadcast capability.  InHARP is the same protocol as the original
   Inverse ARP (InARP) protocol presented in [5] except the HIPPI-6400
   specific packet format.  Knowing its hardware address, InARP is used
   to discover the other party's Internet address.

   This memo further REQUIRES the PIBES (see section 7) extension to the
   HARP protocol, guaranteeing broadcast service to upper layer
   protocols like IP.

   Internet addresses are assigned independent of ULAs.  Before using
   HARP, each node MUST know its IP and its HW addresses. The ULA is
   optional but is RECOMMENDED if interoperability with conventional
   networks is desired.

   If all switches in the LIS support broadcast, then the source address
   in the reply will be the target's source address.  If all switches in
   the LIS do not support broadcast, then a HARP server MUST be used to
   provide the address resolution service, and the source address in the
   reply will be the HARP server's source address.

5.1 HARP Algorithm

   This section defines the behavior and requirements for HARP
   implementations on both broadcast and non-broadcast capable HIPPI-
   6400-SC networks. HARP creates a table in each port which maps remote
   ports' IP addresses to ULAs, so that when an application requests a
   connection to a remote port by its IP address, the remote ULA can be
   determined, a correct HIPPI-6400-PH header can be built, and a
   connection to the port can be established using the ULA.

   HARP is a two phase protocol. The first phase is the registration
   phase and the second phase is the operational phase. In the
   registration phase the port detects if it is connected to broadcast
   hardware or not. The InHARP protocol is used in the registration
   phase.  In case of non-broadcast capable hardware, the InHARP
   Protocol will register and establish a table entry with the server.
   The operational phase works much like conventional ARP with the
   exception of the message format.

5.1.1 Selecting the authoritative HARP service

   Within the HIPPI LIS, there SHALL be an authoritative HARP service.
   To select the authoritative HARP service, each port needs to
   determine if it is connected to a broadcast network. At each point in
   time there is only one authoritative HARP service.

   The port SHALL send an InHARP_REQUEST to the first address in the
   HRAL (FF:FF:FF:FF:FF:FF). If the port sees its own InHARP_REQUEST,
   then it is connected to a broadcast capable network. In this case,
   the rest of the HRAL is ignored and the authoritative HARP service is
   the broadcast entry.

   If the port is connected to a non-broadcast capable network, then the
   port SHALL send the InHARP_REQUEST to all of the remaining entries in
   the HRAL. Every address which sends an InHARP_REPLY is considered to
   be a responsive HARP server. The authoritative HARP service SHALL be
   the HARP server which appears first in the HRAL.

   The order of addresses in the HRAL is only important for deciding
   which address will be the authoritative one. On a non-broadcast
   network, the port is REQUIRED to keep "registered" with all HARP
   server addresses in the HRAL (NOTE: not the broadcast address since

   it is not a HARP server address). If for instance the authoritative
   HARP service is non-responsive,  then the port will consider the next
   address in the HRAL as a candidate for the authoritative address and
   send an InHARP_REQUEST.

   The authoritative HARP server SHOULD be considered non-responsive
   when it has failed to reply to: (1) one or more registration requests
   by the client (see section 5.1.2 and 5.2), (2) any two HARP_REQUESTs
   in the last 120 seconds or (3) if an external agent has detected
   failure of the authoritative HARP server. The details of such an
   external agent and its interaction with the HARP client are beyond
   the scope of this document. Should an authoritative HARP server
   become non-responsive, then the registration process SHOULD be
   restarted. Alternative methods for choosing an authoritative HARP
   service are not prohibited.

5.1.2  HARP registration phase

   HARP clients SHALL initiate the registration phase by sending an
   InHARP_REQUEST message using the HRAL addresses in order. The client
   SHALL terminate the registration phase and transition into the
   operational phase, when either: (1) it receives its own
   InHARP_REQUEST, or (2) when it receives an InHARP_REPLY from at least
   one of the HARP servers and it has determined the authoritative HARP
   service as described in 5.1.1.

   When ports are initiated they send an InHARP_REQUEST to the
   authoritative HRAL address. The first address to be tried will be the
   broadcast address "FF:FF:FF:FF:FF:FF". There are two outcomes:

   1. The port sees its own InHARP_REQUEST: then the port is connected
      to a broadcast capable network. The first address becomes, and
      remains, the authoritative address for the HARP service.

   2. The port does not receive its InHARP_REQUEST: then the port is
      connected to a non-broadcast capable network.

      The port SHALL choose the next address in the HRAL as a candidate
      for a HARP server and send an InHARP_REQUEST to that address:
      (00:10:3B:FF:FF:E0).

      The port SHALL continue to retry each non-broadcast HARP server
      address in the HRAL at least once every 5 seconds until one of the
      following termination criteria are met for each address.

      a. If the port receives its own message, then the port itself is
         the HARP server and the port is REQUIRED to provide broadcast
         services using the PIBES (see section 7).

      b. If the port receives an InHARP_REPLY, then it is a HARP client
         and not a HARP server. In both cases, the current candidate
         address becomes the authoritative HARP service address.

   InHARP is an application of the InARP protocol for a purpose not
   originally intended.  The purpose is to accomplish registration of
   port IP address mappings with a HARP server if one exists or detect
   hardware broadcast capability.

   If the HIPPI-6400-SC LAN supports broadcast, then the client will see
   its own InHARP_REQUEST message and SHALL complete the registration
   phase. The client SHOULD further note that it is connected to a
   broadcast capable network and use this information for aging the HARP
   server entry and for IP broadcast emulation as specified in sections
   5.4 and 5.6 respectively.

   If the client doesn't see its own InHARP_REQUEST it SHALL await an
   InHARP_REPLY before completing the registration phase. This will also
   provide the client with the protocol address by which the HARP server
   is addressable.  This will be the case when the client happens to be
   connected to a non-broadcast capable HIPPI-6400-SC network.

5.1.3 HARP operational phase

   Once a HARP client has completed its registration phase it enters the
   operational phase. In this phase of the protocol, the HARP client
   SHALL gain and refresh its own HARP table information about other IP
   members by sending of HARP_REQUESTs to the authoritative address in
   the HRAL and by receiving of HARP_REPLYs. The client is fully
   operational during the operational phase.

   In the operational phase, the client's behavior for requesting HARP
   resolution is the same for broadcast or non-broadcast HIPPI-6400-SC
   switched networks.

   The target of an address resolution request updates its address
   mapping tables with any new information it can find in the request.
   If it is the target port it SHALL formulate and send a reply message.
   A port is the target of an address resolution request if at least ONE
   of the following statements is true of the request:

   1. The port's IP address is in the target protocol address field
      (ar$tpa) of the HARP message.

   2. The port's ULA, is in the ULA part of the Target Hardware Address
      field (ar$tha) of the message.

   3. The port is a HARP server.

   NOTE: It is REQUIRED to have a HARP server run on a port that has a
   non-zero ULA.

5.2 HARP Client Operational Requirements

   The HARP client is responsible for contacting the HARP server(s) to
   have its own HARP information registered and to gain and refresh its
   own HARP entry/information about other IP members. This means, as
   noted above, that HARP clients MUST be configured with the hardware
   address  of the HARP server(s) in the HRAL.

   HARP clients MUST:

   1. When an interface is enabled (e.g. "ifconfig <interface> up" with
      an IP address) or assigned the first or an additional IP address
      (i.e. an IP alias), the client SHALL initiate the registration
      phase.

   2. In the operational phase the client MUST respond to HARP_REQUEST
      and InHARP_REQUEST messages if it is the target port.  If an
      interface has multiple IP addresses (e.g., IP aliases) then the
      client MUST cycle through all the IP addresses and generate an
      InHARP_REPLY for each such address. In that case an InHARP_REQUEST
      will have multiple replies. (Refer to Section 7, "Protocol
      Operation" in RFC-1293 [5].)

   3. React to address resolution reply messages appropriately to build
      or refresh its own client HARP table entries. All solicited and
      unsolicited HARP_REPLYs from the authoritative HARP server SHALL
      be used to update and refresh its own client HARP table entries.

      Explanation: This allows the HARP server to update the clients
      when one of server's mappings change, similar to what is
      accomplished on Ethernet with gratuitous ARP.

   4. Generate and transmit InHARP_REQUEST messages as needed and
      process InHARP_REPLY messages appropriately (see section 5.1.3 and
      5.6). All InHARP_REPLY messages SHALL be used to build/refresh its
      client HARP table entries.  (Refer to Section 7, "Protocol
      Operation" in [5].)

   If the registration phase showed that the hardware does not support
   broadcast, then the client MUST refresh its own entry for the HARP
   server, created during the registration phase, at least once every 15
   minutes. This can be accomplished either through the exchange of a
   HARP request/reply with the HARP server or by repeating step 1. To
   decrease the redundant network traffic, this timeout SHOULD be reset
   after each HARP_REQUEST/HARP_REPLY exchange.

   Explanation: The HARP_REQUEST shows the HARP server that the client
   is still alive. Receiving a HARP_REPLY indicates to the client that
   the server must have seen the HARP_REQUEST.

   If the registration phase showed that the underlying network supports
   broadcast, then the refresh sequence is NOT REQUIRED.

5.3 Receiving Unknown HARP Messages

   If a HARP client receives a HARP message with an operation code
   (ar$op) that it does not support, it MUST gracefully discard the
   message and continue normal operation.  A HARP client is NOT REQUIRED
   to return any message to the sender of the undefined message.

5.4 HARP Server Operational Requirements

   A HARP server MUST accept HIPPI-6400 connections from other HIPPI-
   6400 ports. The HARP server expects an InHARP_REQUEST as the first
   message from the client. A server examines the IP address, the
   hardware address of the InHARP_REQUEST and adds or updates its HARP
   table entry <IP address(es), ULA> as well as the time stamp.

   A HARP server replies to HARP_REQUESTs and InHARP_REQUESTs based on
   the information which it has in its table. The HARP server replies
   SHALL contain the hardware type and corresponding format of the
   request (see also sec. 6).

   The following table shows all possible source address combinations on
   an incoming message and the actions to be taken. "linked" indicates
   that an existing "IP entry" is linked to a "hardware entry". It is
   possible to have an existing "IP entry" and to have an existing
   "hardware entry" but neither is linked to the other.

      +---+----------+----------+------------+---------------------+
      | # | IP entry | HW entry |  misc      |       Action        |
      +---+----------+----------+------------+---------------------+
      | 1 |  exists  |  exists  |     linked | *                   |
      | 2 |  exists  |  exists  | not linked | *, a, b,       e, f |
      | 3 |  exists  |    new   | not linked | *, a, b, d,    e, f |
      | 4 |   new    |  exists  | not linked | *,       c,    e, f |
      | 5 |   new    |    new   | not linked | *,       c, d, e, f |
      +---+----------+----------+------------+---------------------+
      Actions:
      *: update timeout value
      a: break the existing IP -> hardware (HW) -old link
      b: delete HW(old) -> IP link and decrement HW(old) refcount,
         if refcount = 0, delete HW(old)
      c: create new IP entry

      d: create new HW entry
      e: add new IP -> HW link to IP entry
      f: add new HW -> IP link to HW entry

   Examples of when this could happen (Numbers match lines in above
   table):

   1: supplemental message

      Just update timer.

   2: move an IP alias to an existing interface

      If the IP source address of the InHARP_REQUEST duplicates a table
      entry IP address (e.g. IPa <-> HWa) and the InHARP_REQUEST
      hardware source address matches a hardware address entry (e. g.
      HWb <-> IPb), but they are not linked together, then:

      -  HWa entry needs to have its reference to the current IPa
         address removed.
      -  HWb needs to have a new reference to IPa added
      -  IPa needs to be linked to HWb

      The result will be a table with: IPb <-> HWa <-> IPb  If IPb was
      the only IP address referred to by the HWb entry, then delete the
      HWb entry.

   3: move IP address to a new interface

      If the InHARP_REQUEST requester's IP source address duplicates a
      table entry IP address and the InHARP_REQUEST hardware source
      address does not match the table entry hardware address, then a
      new HW entry SHALL be created. The requestor's IP address SHALL be
      moved from the original HW entry to the new one (see above).

   4: add IP alias to table

      If the InHARP_REQUEST requester's hardware source address
      duplicates a hardware source address entry, but there is no IP
      entry matching the received IP address, then the IP address SHALL
      be added to the hardware entries previous IP address(es). (E.g.
      adding an IP alias).

   5: fresh entry, add it

      Standard case, create both entries and link them.

   A server MUST update the HARP table entry's timeout for each
   HARP_REQUEST. Explanation: if the client is sending HARP requests to
   the server, then the server should note that the client is still
   "alive" by updating the timeout on the client's HARP table entry.

   A HARP server SHOULD use the PIBES (see sect. 7) to send out
   HARP_REPLYs to all hardware addresses in its table when the HARP
   server table changes mappings. This feature decreases the time of
   stale entries in the clients.

   If there are multiple addresses in the HRAL, then a server needs to
   act as a client to the other servers.

5.5 HARP and Permanent ARP Table Entries

   An IP station MUST have a mechanism (e.g. manual configuration) for
   determining what permanent entries it has. The details of the
   mechanism are beyond the scope of this memo.  The permanent entries
   allow interoperability with legacy HIPPI adapters which do not yet
   implement dynamic HARP and use a table based static ARP. Permanent
   entries are not aged.

   The HARP server SHOULD use the static entries to resolve incoming
   HARP_REQUESTs from the clients. This feature eliminates the need for
   maintaining a static HARP table on the client ports.

5.6 HARP Table Aging

   HARP table aging MUST be supported since IP addresses, especially IP
   aliases and also interfaces (with their ULA), are likely to move.
   When so doing the mapping in the clients own HARP table/cache becomes
   invalid and stale.

   o  When a client's HARP table entry ages beyond 15 minutes, a HARP
      client MUST invalidate the table entry.

   o  When a server's HARP table entry ages beyond 20 minutes, the HARP
      server MUST delete the table entry.

   NOTE: the client SHOULD revalidate a HARP table entry before it ages,
   thus restarting the aging time when the table entry is successfully
   revalidated.  The client MAY continue sending traffic to the port
   referred to by this entry while revalidation is in progress, as long
   as the table entry has not aged. The client MUST revalidate the
   invalidated entry prior to transmitting any non-address resolution
   traffic to the port referred to by this entry.

   The client revalidates the entry by querying the HARP server.  If a
   valid reply is received (e.g. HARP_REPLY), the entry is updated.  If
   the address resolution service cannot resolve the entry (e.g.
   HARP_NAK, "host not found"), the associated table entry is removed.
   If the address resolution service is not available (i.e. "server
   failure") the client MUST attempt to revalidate the entry by
   transmitting an InHARP_REQUEST to the hardware address of the entry
   in question and updating the entry on receipt of an InHARP_REPLY. If
   the InHARP_REQUEST attempt fails to return an InHARP_REPLY, the
   associated table entry is removed.

6. HARP Message Encoding

   The HARP message is another type of IEEE 802 payload as described in
   section 4.1.3 above. The HIPPI-6400 HARP SHALL support two packet
   formats, both the generic Ethernet ARP packet and the HIPPI-800 HARP
   packet format defined in [13]. HARP messages SHALL be transmitted
   with a hardware type code of 28 on non-broadcast capable hardware or
   1 in either case.

   The ar$hrd field SHALL be used to differentiate between the two
   packet formats. The reply SHALL be in the format of the request.

6.1 Generic IEEE 802 ARP Message Format

   This is the ARP packet format used by conventional IEEE 802 networks
   (i.e. Ethernet, etc). The packet format is described in RFC-826 [14]
   and is given here only for completeness purpose.

     ar$hrd  16 bits  Hardware type
     ar$pro  16 bits  Protocol type of the protocol fields below
     ar$hln   8 bits  byte length of each hardware address
     ar$pln   8 bits  byte length of each protocol address
     ar$op   16 bits  opcode (ares_op$REQUEST | ares_op$REPLY)
     ar$sha  48 bits  Hardware address of sender of this packet
     ar$spa  32 bits  Protocol address of sender of this packet
     ar$tha  48 bits  Hardware address of target of this
     ar$tpa  32 bits  Protocol address of target.

   Where:
     ar$hrd  - SHALL contain 1. (Ethernet)

     ar$pro  - SHALL contain the IP protocol code 2048 (decimal).

     ar$hln  - SHALL contain 6.

     ar$pln  - SHALL contain 4.

     ar$op   - SHALL contain the operational value (decimal):
               1  for   HARP_REQUESTs
               2  for   HARP_REPLYs
               8  for InHARP_REQUESTs
               9  for InHARP_REPLYs
               10 for   HARP_NAK

     ar$rpa  - in requests and NAKs it SHALL contain the requester's IP
               address if known, otherwise zero.
               In other replies it SHALL contain the target
               port's IP address.

     ar$sha  - in requests and NAKs it SHALL contain the requester's ULA
               In replies it SHALL contain the target port's ULA.

     ar$spa  - in requests and NAKs it SHALL contain the requester's IP
               address if known, otherwise zero.
               In other replies it SHALL contain the target
               port's IP address.

     ar$tha  - in requests and NAKs it SHALL contain the target's ULA
               if known, otherwise zero.
               In other replies it SHALL contain the requester's ULA.

     ar$tpa  - in requests and NAKs it SHALL contain the
               target's IP address if known, otherwise zero.
               In other replies it SHALL contain the requester's
               IP address.

   |31             |23             |15             |7             0|
   +---------------+---------------+---------------+---------------+-----
 0 |                                                               |
   |         D_ULA                 +-------------------------------+HIPPI
 1 |                               |                               |6400
   +-------------------------------+            S_ULA              |MAC
 2 |                                                               |hdr
   +---------------------------------------------------------------+
 3 |                             M_len                             |
   +---------------+---------------+---------------+---------------+-----
 4 |      AA       |       AA      |       03      |      00       |IEEE
   +---------------+---------------+---------------+---------------+802
 5 |       00      |       00      |  Ethertype  =  0x0800 = 2048  |LLC/
   +------------+------------------+-------------------------------+SNAP
 6 |            hrd (1)            |           pro (2048)          |
   +---------------+---------------+---------------+---------------+
 7 |     hln (6)   |   phl (4)     |             op (ar$op)        |
   +<><><><><><><><+><><><><><><><>+<><><><><><><><+><><><><><><><>+
 8 |              Source Hardware Address  0 - 3                   |
   +-------------------------------+-------------------------------+
 9 | Source ULA bytes 4 - 5        | Source IP Address bytes 0 - 1 |
   +-------------------------------+-------------------------------+
10 | Source IP Address bytes 2 - 3 |    Target ULA bytes 0 - 1     |
   +-------------------------------+-------------------------------+
11 |           Target Hardware Address (ULA) bytes 2 - 5           |
   +---------------------------------------------------------------+
12 |                         Target IP Address                     |
   +---------------+---------------+---------------+---------------+
13 |     FILL      |     FILL      |      FILL     |     FILL      |
   +---------------+---------------+---------------+---------------+
14 |     FILL      |     FILL      |      FILL     |     FILL      |
   +><><><><><><><>+<><><><><><><><+><><><><><><><>+<><><><><><><><+

6.2 HIPARP Message Formats

   The HARP protocols further SHALL support the HIPARP hardware type
   (ar$hrd) = 28 (dec) [18], protocol type (ar$pro), and operation code
   (ar$op) data formats as the ARP, and InARP protocols [14,7]. In
   addition, HARP makes use of an additional operation code for ARP_NAK
   introduced with [11]. The remainder of the HIPARP message format
   (defined in [13]) is different than the ARP/InARP message format
   defined in [14,7,10] and it is also different from the format defined
   in the first "IP and ARP on HIPPI" RFC-1374 [16].

   The HARP message has several fields that have the following format
   and values:

   Data sizes and field meaning:
     ar$hrd  16 bits  Hardware type
     ar$pro  16 bits  Protocol type of the protocol fields below
     ar$op   16 bits  Operation code (request, reply, or NAK)
     ar$pln   8 bits  byte length of each protocol address
     ar$rhl   8 bits  requester's HIPPI hardware address length (q)
     ar$thl   8 bits  target's HIPPI hardware address length (x)
     ar$rpa  32 bits  requester's protocol address
     ar$tpa  32 bits  target's protocol address
     ar$rha  qbytes   requester's HIPPI Hardware address
     ar$tha  xbytes   target's HIPPI Hardware address

   Where :
     ar$hrd  - SHALL contain 28. (HIPARP)

     ar$pro  - SHALL contain the IP protocol code 2048 (decimal).

     ar$op   - SHALL contain the operational value (decimal):
               1  for   HARP_REQUESTs
               2  for   HARP_REPLYs
               8  for InHARP_REQUESTs
               9  for InHARP_REPLYs
               10 for   HARP_NAK

     ar$pln  - SHALL contain 4.

     ar$rln  - SHALL contain 10 IF this is a HIPPI-800 HW address
               ELSE, for HIPPI-6400, it SHALL contain 6.

     ar$thl  - SHALL contain 10 IF this is a HIPPI-800 HW address
               ELSE, for HIPPI-6400, it SHALL contain 6.

     ar$rha  - in requests and NAKs it SHALL contain the requester's
               HW address.
               In replies it SHALL contain the target port's HW address.

     ar$rpa  - in requests and NAKs it SHALL contain the requester's IP
               address if known, otherwise zero.
               In other replies it SHALL contain the target
               port's IP address.

     ar$tha  - in requests and NAKs it SHALL contain the target's
               HW address if known, otherwise zero.

               In other replies it SHALL contain the requester's
               HW address.

     ar$tpa  - in requests and NAKs it SHALL contain the
               target's IP address if known, otherwise zero.
               In other replies it SHALL contain the requester's
               IP address.

                  Payload Format for HARP/InHARP PDUs:

   |31             |23             |15             |7             0|
   +---------------+---------------+---------------+---------------+-----
 0 |                                                               |
   |         D_ULA                 +-------------------------------+HIPPI
 1 |                               |                               |6400
   +-------------------------------+            S_ULA              |MAC
 2 |                                                               |hdr
   +---------------------------------------------------------------+
 3 |                             M_len                             |
   +---------------+---------------+---------------+---------------+-----
 4 |      AA       |       AA      |       03      |      00       |IEEE
   +---------------+---------------+---------------+---------------+802
 5 |       00      |       00      |  Ethertype  =  0x0800 = 2048  |LLC/
   +------------+------------------+-------------------------------+SNAP
 6 |            hrd (28)           |           pro (2048)          |
   +---------------+---------------+---------------+---------------+
 7 |             op (ar$op)        |     pln (6)   |   shl (q)     |
   +<><><><><><><><+><><><><><><><>+<><><><><><><><+><><><><><><><>+
 8 |    thl (x)    |      Source IP Address upper (24 bits)        |
   +---------------------------------------------------------------+
 9 | Src. IP lower |      Target IP Address upper (24 bits)        |
   +---------------+-----------------------------------------------+
10 | Tgt. IP lower |       Source HW Address bytes 0 - 2           |
   +---------------+-------------------------------+---------------+
11 |   Source HW Address bytes 3 - q               | Tgt HW byte 0 |
   +-----------------------------------------------+---------------+
12 |              Target Hardware Address bytes 1 - 4              |
   +---------------+-----------------------------------------------+
13 |Tgt HW byte 5-x|
   +---------------+
                          HARP - InHARP Message

6.2.1 Example Message encodings:

   Assume for the following example that the HARP server is in the
   HIPPI-6400 side and the clients, X and Y are on the HIPPI-800 side of
   the non-broadcast capable network.

   HARP_REQUEST message
         HARP ar$op   = 1 (HARP_REQUEST)
         HARP ar$rpa  = IPy                HARP ar$tpa  = IPx
         HARP ar$rha  = SWy ULAy           HARP ar$tha  = **
         ** is what we would like to find out

   HARP_REPLY message format
         HARP ar$op   = 2 (HARP_REPLY)
         HARP ar$rpa  = IPx                HARP ar$tpa  = IPy
         HARP ar$rha  = SWx ULAx *         HARP ar$tha  = SWy ULAy
         * answer we were looking for

   InHARP_REQUEST message format
         HARP ar$op    = 8 (InHARP_REQUEST)
         HARP ar$rpa   = IPy               HARP ar$tpa   = 0 **
         HARP ar$rha   = SWy ULAy          HARP ar$tha   = SWx ULAx
         ** is what we would like to find out

   InHARP_REPLY message format
         HARP ar$op    = 9 (InHARP_REPLY)
         HARP ar$rpa   = IPx *             HARP ar$tpa   = IPy
         HARP ar$rha   = SWx ULAx          HARP ar$tha   = SWy ULAy
         * answer we were looking for

6.2.2 HARP_NAK message format

   The HARP_NAK message format is the same as the received HARP_REQUEST
   message format with the operation code set to HARP_NAK; i.e. the
   HARP_REQUEST message data is copied for transmission with the
   HARP_REQUEST operation code changed to the HARP_NAK value.  HARP
   makes use of an additional operation code for HARP_NAK and MUST be
   implemented.

7  Broadcast and Multicast

   HIPPI-6400-SC requires compliant systems to support broadcast.
   Initial HIPPI-6400-SC systems MAY defer broadcast capability to a
   broadcast server rather than support it directly in the switching
   mechanism.  A centralized HARP server architecture meets two of the
   three major duties of a broadcast server.

   A central entity serving the whole LIS solves the coordination
   problem of a distributed approach. The registration requirement
   solves the second problem of determining which addresses make up the
   set loosely called "everyone". The last duty of a broadcast server is
   to replicate an incoming packet and send it to "everyone".

   During its registration phase, every port , including HARP server(s),
   discover if the underlying medium is capable of broadcast (see
   section 5.1.1). Should this not be the case, then the HARP server(s)
   MUST emulate broadcast through an IP broadcast emulation server.

   A HIPPI IP broadcast server (PIBES) is an extension to the HARP
   server and only makes sense when the LIS does not inherently support
   broadcast. The PIBES allows common upper layer networking protocols
   (RIP, TCP, UDP, etc.)to access IP LIS broadcast.

7.1 Protocol for an IP Broadcast Emulation Server - PIBES

   To emulate broadcast within an LIS, a PIBES SHALL use the currently
   valid HARP table of the HARP server as a list of addresses called the
   target list. The broadcast server SHALL validate that all incoming
   messages have a source address which corresponds to an address in the
   target list. Only messages addressed to the IP LIS broadcast
   addresses, multicast address or 255.255.255.255 are considered valid
   messages for broadcasting. Invalid messages MUST be dropped.  All
   valid incoming messages shall be forwarded to all addresses in the
   target list.

   It is RECOMMENDED that the broadcast server run on the same port as
   the HARP server since this memo does not define the protocol for
   exchanging the valid HARP table. The default address to use for the
   broadcast address is the operational HARP server address.

7.2 IP Broadcast Address

   This memo only defines IP broadcast. It is independent of the
   underlying hardware addressing and broadcast capabilities. Any port
   can differentiate between IP traffic directed to itself and a
   broadcast message sent to it by looking at the IP address. All IP
   broadcast messages SHALL use the IP LIS broadcast address.

   It is RECOMMENDED that the PIBES run on the same port as the HARP
   server. In that case, the PIBES SHALL use the same address as the
   HARP server.

7.3 IP Multicast Address

   HIPPI-6400 does not directly support multicast address, therefore
   there are no mappings available from IP multicast addresses to HIPPI
   multicast services.  Current IP multicast implementations (i.e. MBONE
   and IP tunneling, see [7]) will continue to operate over HIPPI-based
   logical IP subnets if all IP multicast packets are sent using the
   same algorithm as if the packet were being sent to 255.255.255.255.

7.4 A Note on Broadcast Emulation Performance

   It is obvious that a broadcast emulation service (as defined in
   section 7.1) has an inherent performance limit. In an LIS with n
   ports, the upper bound on the bandwidth that such a service can
   broadcast is:

                          (total bandwidth)/(n+1)

   since each message must first enter the broadcast server, accounting
   for the additional 1, and then be sent to all n ports. The broadcast
   server could forward the message destined to the port on which it
   runs internally, thus reducing (n+1) to (n) in a first optimization.

   This service is adequate for the standard networking protocols such
   as RIP, OSPF, NIS, etc. since they usually use a small fraction of
   the network bandwidth for broadcast. For these purposes, the
   broadcast emulation server as defined in this memo allows the HIPPI-
   6400 network to look similar to an Ethernet network to the higher
   layers.

   It is further obvious that such an emulation cannot be used to
   broadcast high bandwidth traffic. For such a solution, hardware
   support for true broadcast is required.

8 HARP for Scheduled Transfer

   This RFC also applies for resolving addresses used with Scheduled
   Transfer (ST) over HIPPI-6400 instead of IP. This RFC's message types
   and algorithms can be used for ST (since ST uses Internet Addresses)
   as long as there is also an IP over HIPPI-6400 implementation on all
   the ports.

9 Security Consierations

   There are known security issues relating to port impersonation via
   the address resolution protocols used in the Internet [6].  No
   special security mechanisms have been added to the address resolution
   mechanism defined here for use with networks using HARP.

   Not all of the security issues relating to ARP over HIPPI-6400 are
   clearly understood at this time, due to the fluid state of HIPPI-6400
   specifications, newness of the technology, and other factors.
   However, given the security hole ARP allows, other concerns are
   probably minor.

10 Open Issues

   Synchronization and coordination of multiple HARP servers and
   multiple broadcast servers are left for further study.

11 HARP Examples

   Assume a HIPPI-6400-SC switch is installed with three connected
   ports:  x, y, and a. Each port has a unique hardware address that
   consists unique ULA (ULAx, ULAy and UlAa, respectively). There is a
   HARP server connected to a switch port that is mapped to the address
   HWa, this address is the authoritative HIPPI hardware address in the
   HRAL (HARP Request Address List).

   The HARP server's table is empty. Ports X and Y each know their own
   hardware address.  Eventually they want to talk to each other; each
   knows the other's IP address (from the port database) but neither
   knows the other's ULA. Both ports X and Y have their interfaces
   configured DOWN.

   NOTE: The LLC, SNAP, Ethertype, ar$hrd, ar$pro, ar$pln fields are
   left out from the examples below since they are constant. As well as
   ar$rhl = ar$thl = 6 since these are all HIPPI-6400 examples.

11.1 Registration Phase of Client Y on Non-broadcast Hardware

   Port Y starts: its HARP table entry state for the server: PENDING

   1. Port Y initiates its interface and sends an InHARP_REQUEST to the
      HWa after starting a table entry for the HWa.

      HIPPI-6400-PH D_ULA                 = ULAa
      HIPPI-6400-PH S_ULA                 = ULAy
      HARP ar$op                          = 8 (InHARP_REQUEST)
      HARP ar$rpa                         = IPy
      HARP ar$tpa                         = 0 **
      HARP ar$rha                         = ULAy
      HARP ar$tha                         = ULAa
      ** is what we would like to find out

   2. HARP server receives Y's InHARP_REQUEST, it examines the source
      addresses and scans its tables for a match. Since this is the
      first time Y connects to this server there is no entry and one
      will be created and time stamped with the information from the
      InHARP_REQUEST. The HARP server will then send a InHARP_REPLY
      including its IP address.

      HIPPI-6400-PH D_ULA                 = ULAy
      HIPPI-6400-PH S_ULA                 = ULAa
      HARP ar$op                          = 9 (InHARP_REPLY)
      HARP ar$rpa                         = IPs *
      HARP ar$tpa                         = IPy
      HARP ar$rha                         = ULAa
      HARP ar$tha                         = ULAy
      * answer we were looking for

   3. Port Y examines the incoming InHARP_REPLY and completes its table
      entry for the HARP server. The client's HARP table entry for the
      server now passes into the VALID state and is usable for regular
      HARP traffic. Receiving this reply ensures that the HARP server
      has properly registered the client.

11.2 Registration Phase of Client Y on Broadcast Capable Hardware

   If port Y is connected to a broadcast-capable network then the
   authoritative address is the broadcast address, HWb = SWb, ULAb
   (FF:FF:FF:FF:FF:FF).

   Port Y starts: its HARP table entry state for HWa: PENDING

   1. Port Y initiates its interface and sends an InHARP_REQUEST to HWa,
      in this example the broadcast address, after starting a table
      entry.

      HIPPI-6400-PH D_ULA                 = ULAb
      HIPPI-6400-PH S_ULA                 = ULAy
      HARP ar$op                          = 8 (InHARP_REQUEST)
      HARP ar$rpa                         = IPy
      HARP ar$tpa                         = 0 **
      HARP ar$rha                         = ULAy
      HARP ar$tha                         = ULAb
      ** is what we would like to find out

   2. Since the network is a broadcast network, client Y will receive a
      copy of its InHARP_REQUEST. Client Y examines the source
      addresses.  Since they are the same as what Y filled in the
      InHARP_REQUEST, Y can deduce that it is connected to a broadcast
      medium.  Port Y completes its table entry for HWa. This entry will
      not timeout since it is considered unlikely for a particular
      underlying hardware type to change between broadcast and non-
      broadcast; therefore this mapping will never change.

11.3 Operational Phase (phase II)

   The Operational Phase of the HARP protocol as specified in this memo
   is the same for both broadcast and non-broadcast capable HIPPI-6400
   hardware. The authoritative address in the HRAL for this example will
   be HWa: <SWa, ULAa> and IPs for simplicity reasons.

11.3.1 Successful HARP_Resolve example

   Assume the same process (steps 1-3 of section 11.1) happened for port
   X. Then the state of X and Y's tables is: the HARP server table entry
   is in the VALID state. So lets look at the message traffic when X
   tries to send a message to Y. Since X doesn't have an entry for Y,

   1. Port X connects to the authoritative address of the HRAL and sends
      a HARP_REQUEST for Y's hardware address:

      HIPPI-6400-PH D_ULA                 = ULAa
      HIPPI-6400-PH S_ULA                 = ULAx
      HARP ar$op                          = 1  (HARP_REQUEST)
      HARP ar$rpa                         = IPx
      HARP ar$tpa                         = IPy
      HARP ar$rha                         = ULAx
      HARP ar$tha                         = 0 **
      ** is what we would like to find out

   2. The HARP server receives the HARP request and updates its entry
      for X if necessary. It then generates a HARP_REPLY with Y's
      hardware address information.

      HIPPI-6400-PH D_ULA                 = ULAx
      HIPPI-6400-PH S_ULA                 = ULAa
      HARP ar$op                          = 2  (HARP_Reply)
      HARP ar$rpa                         = IPy
      HARP ar$tpa                         = IPx
      HARP ar$rha                         = ULAy *
      HARP ar$tha                         = ULAx
      * answer we were looking for

   3. Port X connects to port Y and transmits an IP message with the
      following information in the HIPPI-LE header:

      HIPPI-6400-PH D_ULA                 = ULAy
      HIPPI-6400-PH S_ULA                 = ULAx
      <data>

   If the network had been broadcast-capable, the target ports would
   themselves have received the HARP_REQUEST of step 2 above and
   responded to them in the same way the HARP server did.

11.3.2 Non-successful HARP_Resolve example

   As in 11.3.1, assume that X and Y are fully registered with the HARP
   server. Then the state of X and Y's HARP server table entry is:
   VALID. So lets look at the message traffic when X tries to send a
   message to Q. Further assume that interface Q is NOT configured UP,
   i.e. it is DOWN.  Since X doesn't have an entry for Q,

   1. Port X connects to the HARP server switch address and sends a
      HARP_REQUEST for Q's hardware address:

      HIPPI-6400-PH D_ULA                 = ULAa
      HIPPI-6400-PH S_ULA                 = ULAx
      HARP ar$op                          = 1  (HARP_REQUEST)
      HARP ar$rpa                         = IPx
      HARP ar$tpa                         = IPq
      HARP ar$rha                         = ULAx
      HARP ar$tha                         = 0 **
      ** is what we would like to find out

   2. The HARP server receives the HARP request and updates its entry
      for X if necessary. It then looks up IPq in its tables and doesn't
      find it. The HARP server then generates a HARP_NAK reply message.

      HIPPI-6400-PH D_ULA                 = ULAx
      HIPPI-6400-PH S_ULA                 = ULAa
      HARP ar$op                          = 10  (HARP_NAK)
      HARP ar$rpa                         = IPx
      HARP ar$tpa                         = IPq
      HARP ar$rha                         = ULAx
      HARP ar$tha                         = 0 ***
      *** No Answer, and notice that the fields do not get swapped,
          i.e. the HARP message is the same as the HARP_REQUEST
          except for the operation code.

   If the network had been broadcast-capable, then there would not have
   been a reply.

12 References

   [1]  ANSI NCITS 323-1998, Information Technology - High-Performance
        Parallel Interface - 6400 Mbit/s Physical Layer (HIPPI-6400-PH).

   [2]  ANSI NCITS 324-199x, Information Technology - High-Performance
        Parallel Interface - 6400 Mbit/s Physical Switch Control
        (HIPPI-6400-SC).

   [3]  ANSI NCITS Project Number 1249-D, Information Technology -
        High-Performance Parallel Interface - 6400 Mbit/s Optical
        Specification (HIPPI-6400-OPT).

   [4]  Braden, R., "Requirements for Internet Hosts -- Communication
        Layers", STD 3, RFC 1122, October 1989.

   [5]  Bradely, T. and C. Brown, "Inverse Address Resolution Protocol",
        RFC 2390, September 1998.

   [6]  Bellovin, Steven M., "Security Problems in the TCP/IP Protocol
        Suite", ACM Computer Communications Review, Vol. 19, Issue 2,
        pp.  32-48, 1989.

   [7]  Deering, S, "Host Extensions for IP Multicasting", STD 5, RFC
        1112, August 1989.

   [8]  Chesson, Greg, "HIPPI-6400 Overview", IEEE Hot Interconnects
        1996, Stanford University.

   [10] ANSI/IEEE Std. 802.2-1989, Information Processing Systems -
        Local Area Networks - Logical Link Control IEEE, IEEE, New York,
        New York, 1989.

   [11] Laubach, M., "Classical IP and ARP over ATM", RFC 2225, April
        1998.

   [12] Mogul, J. and S. Deering, "Path MTU Discovery", RFC 1191,
        November, 1990.

   [13] Pittet, J.-M., "ARP and IP Broadcast over HIPPI-800", RFC 2834,
        May 2000.

   [14] Plummer, D., "An Ethernet Address Resolution Protocol - or -
        Converting Network Addresses to 48-bit Ethernet Address for
        Transmission on Ethernet Hardware", RFC-826, MIT, November 1982.

   [15] Postel, J., "Internet Protocol", STD 5, RFC 791, September 1981.

   [16] Renwick, J. and A. Nicholson, "IP and ARP on HIPPI", RFC 1374,
        October 1992.

   [17] Renwick, J., "IP over HIPPI", RFC 2067, January 1997.

   [18] Reynolds, J. and J. Postel, "Assigned Numbers", STD 2, RFC 1700,
        October 1994.

   [19] Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", BCP 14, RFC 2119, March 1997.

13 Acknowledgments

   This memo could not have come into being without the critical review
   from Greg Chesson, Carlin Otto, the High performance interconnect
   group of Silicon Graphics (specifically Jim Pinkerton, Brad Strand
   and Jeff Young) and the expertise of the ANSI T11.1 Task Group
   responsible for the HIPPI standards work.

   This memo is based on the second part of [17], written by John
   Renwick. ARP [14] written by Dave Plummer and Inverse ARP [7] written
   by Terry Bradley and Caralyn Brown provide the fundamental algorithms
   of HARP as presented in this memo. Further, the HARP server is based
   on concepts and models presented in [13], written by Mark Laubach who
   laid the structural groundwork for the HARP server.

14 Author's Address

   Jean-Michel Pittet
   Silicon Graphics Inc
   1600 Amphitheatre Parkway
   Mountain View, CA 94040

   Phone: 650-933-6149
   Fax:   650-933-3542
   EMail: jmp@sgi.com, jmp@acm.org

15 Full Copyright Statement

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