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See reader questions & answers on this topic! - Help others by sharing your knowledge
Note that this posting has been split into two parts because of its size.

$Id: cptd-faq.bfnn,v 1.26 1999/02/11 20:01:58 cdp Exp cdp $

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 Section 1.  TO DO / UPDATES
 Q1.1        Contributions needed 
 Q1.2        UPDATES / Changes since last posting 

 Q2.1        What is this newsgroup ?
 Q2.2        More information
 Q2.3        What is BIND  ?
 Q2.4        What is the difference between BIND and DNS ?
 Q2.5        Where is the latest version of BIND located ?
 Q2.6        How can I find the path taken between two systems/domains ?
 Q2.7        How do you find the hostname given the TCP-IP address ?
 Q2.8        How do I register a domain ?
 Q2.9        How can I change the IP address of our server ?
 Q2.10       Issues when changing your domain name
 Q2.11       How memory and CPU does DNS use ?
 Q2.12       Other things to consider when planning your servers  
 Q2.13       Reverse domains (IN-ADDR.ARPA) and their delegation 
 Q2.14       How do I get my address assigned from the NIC ?
 Q2.15       Is there a block of private IP addresses I can use?
 Q2.16       Does BIND cache negative answers (failed DNS lookups) ?
 Q2.17       What does an NS record really do ?
 Q2.18       DNS ports
 Q2.19       What is the cache file 
 Q2.20       Obtaining the latest cache file
 Q2.21       Selecting a nameserver/root cache
 Q2.22       Domain names and legal issues
 Q2.23       Iterative and Recursive lookups
 Q2.24       Dynamic DNS
 Q2.25       What version of bind is running on a server ? 
 Q2.26       BIND and Y2K

 Section 3.  UTILITIES 
 Q3.1        Utilities to administer DNS zone files
 Q3.2        DIG - Domain Internet Groper
 Q3.3        DNS packet analyzer
 Q3.4        host
 Q3.5        How can I use DNS information in my program?
 Q3.6        A source of information relating to DNS

 Section 4.  DEFINITIONS  
 Q4.1        TCP/IP Host Naming Conventions
 Q4.2        What are slaves and forwarders ?
 Q4.3        When is a server authoritative?
 Q4.4        My server does not consider itself authoritative !
 Q4.5        NS records don't configure servers as authoritative ?
 Q4.6        underscore in host-/domainnames
 Q4.7        How do I turn the "_" check off ?
 Q4.8        What is lame delegation ?
 Q4.9        How can I see if the server is "lame" ?
 Q4.10       What does opt-class field in a zone file do?
 Q4.11       Top level domains
 Q4.12       US Domain
 Q4.13       Classes of networks
 Q4.14       What is CIDR ?
 Q4.15       What is the rule for glue ?
 Q4.16       What is a stub record/directive ?

 Q5.1        Upgrading from 4.9.x to 8.x 
 Q5.2        Changing a Secondary server to a Primary server ?
 Q5.3        Moving a Primary server to another server
 Q5.4        How do I subnet a Class B Address ?
 Q5.5        Subnetted domain name service
 Q5.6        Recommended format/style of DNS files
 Q5.7        DNS on a system not connected to the Internet
 Q5.8        Multiple Domain configuration
 Q5.9        wildcard MX records
 Q5.10       How do you identify a wildcard MX record ?
 Q5.11       Why are fully qualified domain names recommended ?
 Q5.12       Distributing load using named
 Q5.13       Round robin IS NOT load balancing
 Q5.14       Order of returned records
 Q5.15       resolv.conf
 Q5.16       How do I delegate authority for sub-domains ?
 Q5.17       DNS instead of NIS on a Sun OS 4.1.x system
 Q5.18       Patches to add functionality to BIND 
 Q5.19       How to serve multiple domains from one server
 Q5.20       hostname and domain name the same
 Q5.21       Restricting zone transfers
 Q5.22       DNS in firewalled and private networks
 Q5.23       Modifying the Behavior of DNS with ndots
 Q5.24       Different DNS answers for same RR

 Section 6.  PROBLEMS
 Q6.1        No address for root server
 Q6.2        Error - No Root Nameservers for Class XX
 Q6.3        Bind 4.9.x and MX querying?
 Q6.4        Do I need to define an A record for localhost ?
 Q6.5        MX records, CNAMES and A records for MX targets
 Q6.6        Can an NS record point to a CNAME ?
 Q6.7        Nameserver forgets own A record
 Q6.8        General problems (core dumps !)
 Q6.9        malloc and DECstations
 Q6.10       Can't resolve names without a "."
 Q6.11       Why does swapping kill BIND ?
 Q6.12       Resource limits warning in system
 Q6.13       ERROR:ns_forw: query...learnt 
 Q6.14       ERROR:zone has trailing dot
 Q6.15       ERROR:Zone declared more then once
 Q6.16       ERROR:response from unexpected source
 Q6.17       ERROR:record too short from [zone name]
 Q6.18       ERROR:sysquery: findns error (3)
 Q6.19       ERROR:Err/TO getting serial# for XXX
 Q6.20       ERROR:zonename IN NS points to a CNAME
 Q6.21       ERROR:Masters for secondary zone [XX] unreachable
 Q6.22       ERROR:secondary zone [XX] expired
 Q6.23       ERROR:bad response to SOA query from [address]
 Q6.24       ERROR:premature EOF, fetching [zone]
 Q6.25       ERROR:Zone [XX] SOA serial# rcvd from [Y] is < ours
 Q6.26       ERROR:connect(IP/address) for zone [XX] failed
 Q6.27       ERROR:sysquery: no addrs found for NS
 Q6.28       ERROR:zone [name] rejected due to errors

 Q7.1        How is this FAQ generated ?
 Q7.2        What formats are available ?
 Q7.3        Contributors


Section 1.  TO DO / UPDATES

 Q1.1        Contributions needed 
 Q1.2        UPDATES / Changes since last posting 


Question 1.1.  Contributions needed

Date: Mon Jan 18 22:57:01 EST 1999

* Additional information on the new TLDs
* Expand on Q: How to serve multiple domains from one server
* Q: DNS ports - need to expand/correct some issues


Question 1.2.  UPDATES / Changes since last posting

Date: Thu Feb 11 14:36:02 EST 1999

* DNS in firewalled and private networks - Updated with comment about hint
* host - Updated NT info
* How do I register a domain ? - JP NIC
* BIND and Y2K



 Q2.1        What is this newsgroup ?
 Q2.2        More information
 Q2.3        What is BIND  ?
 Q2.4        What is the difference between BIND and DNS ?
 Q2.5        Where is the latest version of BIND located ?
 Q2.6        How can I find the path taken between two systems/domains ?
 Q2.7        How do you find the hostname given the TCP-IP address ?
 Q2.8        How do I register a domain ?
 Q2.9        How can I change the IP address of our server ?
 Q2.10       Issues when changing your domain name
 Q2.11       How memory and CPU does DNS use ?
 Q2.12       Other things to consider when planning your servers  
 Q2.13       Reverse domains (IN-ADDR.ARPA) and their delegation 
 Q2.14       How do I get my address assigned from the NIC ?
 Q2.15       Is there a block of private IP addresses I can use?
 Q2.16       Does BIND cache negative answers (failed DNS lookups) ?
 Q2.17       What does an NS record really do ?
 Q2.18       DNS ports
 Q2.19       What is the cache file 
 Q2.20       Obtaining the latest cache file
 Q2.21       Selecting a nameserver/root cache
 Q2.22       Domain names and legal issues
 Q2.23       Iterative and Recursive lookups
 Q2.24       Dynamic DNS
 Q2.25       What version of bind is running on a server ? 
 Q2.26       BIND and Y2K


Question 2.1.  What is this newsgroup ?

Date: Thu Dec  1 11:08:28 EST 1994 is the usenet newsgroup for discussion on
issues relating to the Domain Name System (DNS).

This newsgroup is not for issues directly relating to IP routing and
addressing.  Issues of that nature should be directed towards


Question 2.2.  More information

Date: Fri Dec  6 00:41:03 EST 1996

You can find more information concerning DNS in the following places:

* The BOG (BIND Operations Guide) - in the BIND distribution
* The FAQ included with BIND 4.9.5 in doc/misc/FAQ
* DNS and BIND by Albitz and Liu (an O'Reilly & Associates Nutshell
* A number of RFCs (920, 974, 1032, 1034, 1101, 1123, 1178, 1183, 1348,
  1535, 1536, 1537, 1591, 1706, 1712, 1713, 1912, 1918)
* The DNS Resources Directory (DNSRD)
* If you are having troubles relating to sendmail and DNS, you may wish to
  refer to the USEnet newsgroup comp.mail.sendmail and/or the FAQ for that
  newsgroup which may be found for anonymous ftp at :
* Information concerning some frequently asked questions relating to the
  Internet (i.e., what is the InterNIC, what is an RFC, what is the IETF,
  etc) may be found for anonymous ftp from : /fyi/fyi4.txt
  A version may also be obtained with the URL
* Information on performing an initial installation of BIND may be found
  using the DNS Resources Directory at
* Three other USEnet newsgroups:

  * comp.protocols.dns.bind
  * comp.protocols.dns.ops
  * comp.protocols.dns.std


Question 2.3.  What is BIND  ?

Date: Tue Sep 10 23:15:58 EDT 1996

From the BOG Introduction -

The Berkeley Internet Name Domain (BIND)  implements an  Internet name
server  for the BSD operating system.  The BIND consists of  a server (or
``daemon'')  and  a resolver  library.   A  name server is a network
service that enables clients to name  resources or  objects and share this
information with other objects in the network.  This in effect is a
distributed  data  base  system  for objects  in a computer network.  BIND
is fully integrated into BSD (4.3 and later releases) network  programs
for use  in  storing and  retrieving host names and address.  The system
administrator can configure the system to  use BIND as  a replacement to
the older host table lookup of information in the network hosts file
/etc/hosts.   The default configuration for BSD uses BIND.


Question 2.4.  What is the difference between BIND and DNS ?

Date: Tue Sep 10 23:15:58 EDT 1996

(text provided by Andras Salamon) DNS is the Domain Name System, a set of
protocols for a distributed database that was originally designed to
replace /etc/hosts files.  DNS is most commonly used by applications to
translate domain names of hosts to IP addresses.  A client of the DNS is
called a resolver; resolvers are typically located in the application
layer of the networking software of each TCP/IP capable machine.  Users
typically do not interact directly with the resolver.  Resolvers query the
DNS by directing queries at name servers that contain parts of the
distributed database that is accessed by using the DNS protocols.  In
common usage, `the DNS' usually refers just to the data in the database.

BIND (Berkeley Internet Name Domain) is an implementation of DNS, both
server and client.  Development of BIND is funded by the Internet Software
Consortium and is coordinated by Paul Vixie.  BIND has been ported to
Windows NT and VMS, but is most often found on Unix.  BIND source code is
freely available and very complex; most of the development on the DNS
protocols is based on this code; and most Unix vendors ship BIND-derived
DNS implementations.  As a result, the BIND name server is the most widely
used name server on the Internet.  In common usage, `BIND' usually refers
to the name server that is part of the BIND distribution, and sometimes to
name servers in general (whether BIND-derived or not).


Question 2.5.  Where is the latest version of BIND located ?

Date: Mon Sep 14 22:46:00 EDT 1998

This information may be found at

Presently, there are two 'production level' versions of BIND.   They are
versions 4 and 8.

Version 4 is the last "traditional" BIND -- the one everybody on the
Internet runs, except a few hundred sites running...

Version 8 has been called "BIND-ng" (Next Generation).   Many new features
are found in version 8.

BIND-8.1 has the following features:

* DNS Dynamic Updates (RFC 2136)
* DNS Change Notification (RFC 1996)
* Completely new configuration syntax
* Flexible, categorized logging system
* IP-address-based access control for queries, zone transfers, and updates
  that may be specified on a zone-by-zone basis
* More efficient zone transfers
* Improved performance for servers with thousands of zones
* The server no longer forks for outbound zone transfers
* Many bug fixes.

Bind version 8.1.2 may be found at the following location:

* Source : /isc/bind/src/8.1.2/bind-8.1.2-src.tar.gz
* Documentation : /isc/bind/src/8.1.2/bind-8.1.2-doc.tar.gz
* Contributed packages :

At this time, BIND version 4.9.7 may be found for anonymous ftp from : /isc/bind/src/4.9.7/bind-4.9.7-REL.tar.gz

Other sites that officially mirror the BIND distribution are

* : /pub/bind
* : /pub/unix/tcpip/dns/bind
* : /pub/mirrors/unix/bind
* : /pub/mirrors/unix/bind
* : /pub/Unix/dns/bind
* : /pub/unix/dns/bind/beta

You may need GNU zip, Larry Wall's patch program (if there are any patch
files), and a C compiler to get BIND running from the above mentioned

GNU zip is available for anonymous ftp from : /pub/gnu/gzip-1.2.4.tar

patch is available for anonymous ftp from : /pub/gnu/patch-2.1.tar.gz

A version of BIND for Windows NT is available for anonymous ftp from : /isc/bind/contrib/ntbind/

and : /isc/bind/contrib/ntbind/

If you contact, he will send you information
regarding a  Windows NT/WIN95 bind port of 4.9.6 release.

A Freeware version of Bind for NT is available at


Question 2.6.  How can I find the path taken between two systems/domains ?

Date: Wed Jan 14 12:07:03 EST 1998

On a Unix system, use traceroute.  If it is not available to you, you may
obtain the source source for 'traceroute', compile it and install it on
your system.

One version of this program with additional functionality may be found for
anonymous ftp from : /pub/network/traceroute.tar.Z

Another version may be found for anonymous ftp from : /pub/net_tools/traceroute.tar

NT/Windows 95 users may use the command TRACERT.EXE, which is installed
with the TCP/IP protocol support.   There is a Winsock utility called
WS_PING by John Junod that provides ping, traceroute, and nslookup

There are several shareware TCP/IP utilities that provide ping,
traceroute,  and DNS lookup functionality for a Macintosh: Mac TCP Watcher
and  IP Net Monitor are two of them.


Question 2.7.  How do you find the hostname given the TCP-IP address ?

 Mon Jun 15 21:32:57 EDT 1998

For an address a.b.c.d you can always do:

         % nslookup
         > set q=ptr

Most newer version of nslookup (since 4.8.3) will recognize an address, so
you can just say:

         % nslookup a.b.c.d

DiG will work like this also:

         % dig -x a.b.c.d

dig is included in the bind distribution.  host from the bind distribution
may also be used.

On a Macintosh, some shareware utilities may be used.  IP Net Monitor has
a very nice NS Lookup feature, producing DiG-like output; Mac TCP Watcher
just has a simple name-to-address and address-to-name translator.


Question 2.8.  How do I register a domain ?

Date: Thu Feb 11 14:51:50 EST 1999

Procedures for registering a domain name depend on the top level domain
(TLD) to which the desired domain name will belong, i.e. the rightmost
suffix of the desired domain name.  See the answer to "Top level  domains"
question in the DEFINITIONS SECTION of this FAQ.

Although domain registration may be performed by a direct contact with the
appropriate domain registration authorities (domain name registrars), the
easiest way to do it is to talk to your Internet Service Providers. They
can submit a domain registration request on your behalf, as well as to set
up secondary DNS for your domain (or both DNS servers, if you need a
domain name for Web hosting and/or mail delivery purposes only).

In the case where the registration is done by the organization itself, it
still makes the whole process much easier if the ISP is approached for
secondary (see RFC 2182)  servers _before_  the InterNIC is  approached
for registration.

In any case, you will need at least two domain name servers when you
register your domain. Many ISP's are willing to provide primary and/or
secondary name service for their customers.  If you want to register a
domain name ending with .COM, .NET, .ORG, you'll want to take a look to
the InterNIC:

* -> Registration Services
* : /templates/domain-template.txt
* gopher://

Please note that the InterNIC charges a fee for domain names in the "COM",
"ORG", and "NET".  More information may be found from the Internic at

Note that InterNIC doesn't allocate and assign IP numbers any more. Please
refer to the answer to "How do I get my address assigned from the NIC?" in
this section.

Registration of domain names ending with country code suffixes (ISO 3166 -
.FR, .CH, .SE etc.) is being done by the national domain name registrars
(NICs). If you want to obtain such a domain, please refer to the following

Additional domain/whois information may be found:

* http://www.UNINETT.NO/navn/domreg.html
* (with /e at the end of query for English)
* : /pub/whois/whois-servers.list

Many times, registration of a domain name can be initiated by sending
e-mail to the zone contact. You can obtain the contact in the SOA record
for the country, or in a whois server:

         $ nslookup -type=SOA fr.
         origin =
         mail addr =

The mail address to contact in this case is '' (you must
substitute an '@' for the first dot in the mail addr field).

An alternate method to obtain the e-mail address of the national NIC is
the 'whois' server at InterNIC.

You may be requested to make your request to another email address or
using a certain information template/application.  You may be requested to
make your request to another email address or using a certain information
template/application. Please remember that every TLD registrar has its own
registration policies and procedures.


Question 2.9.  How can I change the IP address of our server ?

Date: Wed Jan 14 12:09:09 EST 1998

(From Mark Andrews) Before the move.

* Ensure you are running a modern nameserver. BIND 4.9.6-P1 or 8.1.1 are
  good choices.
* Inform all your secondaries that you are going to change.  Have them
  install both the current and new addresses in their named.boot's.
* Drop the ttl of the A's associated with the nameserver to something
  small (5 min is usually good).
* Drop the refresh and retry times of the zone containing the  forward
  records for the server.
* Configure the new reverse zone before the move and make sure it is
* On the day of the move add the new A record(s) for the server.  Don't
  forget to have these added to parent domains. You will look like you are
  multihomed with one interface dead.

Move the machine after gracefully terminating any other services it is
offering. Then,

* Fixup the A's, ttl, refresh and retry counters.  (If you are running an
  all server EDIT out all references to the old addresses in the cache
* Inform all the secondaries the move is complete.
* Inform the parents of all zones you are primary of the new NS/A pairs
  for the relevant zones.  If you're changing the address of a server
  registered with the InterNIC, you also need to submit a Modify Host form
  to the InterNIC, so they will update the glue records on the root
  servers.  It can take the InterNIC  a few days to process this form, and
  the old glue records have 2-day TTL's,  so this transition may be
* Inform all the administrators of zones you are secondarying that the
  machine  has moved.
* For good measure update the serial no for all zones you are primary for.
  This will flush out old A's.


Question 2.10.  Issues when changing your domain name

Date: Sun Nov 27 23:32:41 EST 1994

If you are changing your domain name from to,
the forward zones are easy and there are a number of ways to do it.   One
way is the following:

Have a single db file for the 2 domains, and have a single machine be the
primary server for both and

To resolve the host foo in both domains, use a single zone file which
merely uses this for the host:

foo             IN      A

Use a "@" wherever the domain would be used ie for the SOA:

@               IN      SOA     (...

Then use this pair of lines in your named.boot:

primary  db.foobar
primary      db.foobar

The reverse zones should either contain PTRs to both names, or to
whichever name you believe to be canonical currently.


Question 2.11.  How memory and CPU does DNS use ?

Date: Fri Dec  6 01:07:56 EST 1996

It can use quite a bit !  The main thing that BIND needs is memory.   It
uses very little CPU or network bandwidth.   The main  considerations to
keep in mind when planning are:

* How many zones do you have and how large are they ?
* How many clients do you expect to serve and how active are they ?

As an example, here is a snapshot of memory usage from CSIRO Division  of
Mathematics and Statistics, Australia

      Named takes several days to stabilize its memory usage.
      Our main server stabalises at ~10Mb. It takes about 3 days to
      reach this size from 6 M at startup. This is under Sun OS 4.1.3U1.

As another example, here is the configuration of (from late
1994): only does nameservice.  It is running a version of BIND
      4.9.3 on a Sun Classic with 96 MB of RAM, 220 MB of swap (remember
      that Sun OS will reserve swap for each fork, even if it is not needed)
      running Sun OS 4.1.3_U1.

      Joseph Malcolm, of Alternet, states that named generally hovers at 
      5-10% of the CPU, except after a reload, when it eats it all. 


Question 2.12.  Other things to consider when planning your servers

Date: Mon Jan  2 14:24:51 EST 1995

When making the plans to set up your servers, you may want to also
consider the following issues:

        A) Server O/S limitations/capacities (which tend to be widely
           divergent from vendor to vendor)
        B) Client resolver behavior (even more widely divergent)
        C) Expected query response time
        D) Redundancy
        E) Desired speed of change propagation
        F) Network bandwidth availability
        G) Number of zones/subdomain-levels desired
        H) Richness of data stored (redundant MX records? HINFO records?)
        I) Ease of administration desired
        J) Network topology (impacts reverse-zone volume)
  Assuming a best-possible case for the factors above, particularly (A), (B),
  (C), (F), (G) & (H), it would be possible to run a 1000-node domain
  using a single lowly 25 or 40 MHz 386 PC with a fairly modest amount of RAM 
  by today's standards, e.g. 4 or 8 Meg.   However, this configuration would 
  be slow, unreliable, and would provide no functionality beyond your basic 
  address-to-name and name-to-address mappings.
  Beyond that baseline case, depending on what factors listed above,
  you may want look at other strategies, such splitting up the DNS
  traffic among several machines strategically located, possibly larger ones,
  and/or subdividing your domain itself. There are many options, tradeoffs, 
  and DNS architectural paradigms from which to choose.


Question 2.13.  Reverse domains (IN-ADDR.ARPA) and their delegation

Date: Mon Jun 15 23:28:47 EDT 1998

(The following section was contributed by Berislav Todorovic.)

Reverse domains (subdomains of the IN-ADDR.ARPA domain) are being used by
the domain name service to perform reverse name mapping - from IP
addresses to host names. Reverse domains are more closely related to IP
address space usage than to the "forward" domain names used. For example,
a host using IP address will have its "reverse" name:, which must be entered in the DNS, by a PTR record:     IN     PTR

In spite of the fact that IP address space is not longer divided into
classes (A, B, C, D, E - see the answer to "What is CIDR?" in the
DEFINITIONS section), the reverse host/domain names are organized on IP
address byte boundaries.  Thus, the reverse host name may belong to one of the following reverse domains,
depending on the address space allocated/assigned to you and your DNS

(1) -> 
       assigned one or more "C class" networks (IP >= /24)
(2)   -> 
       assigned a whole "B class" 10.91/16      (IP = /16)
(3) ISP dependent        -> 
       assigned < "C class" - e.g. 10.91.8/26   (IP < /24)

No matter what is your case (1, 2 or 3) - the reverse domain name must be
properly delegated - registered in the IN-ADDR.ARPA zone. Otherwise,
translation IP -> host name will fail, which may cause troubles when using
some Internet services and accessing some public sites.

To register your reverse domain, talk to your Internet service provider,
to ensure proper DNS configuration, according to your network topology and
address space assigned. They will point you to a further instance, if
necessary. Generally speaking, while forward domain name registration is a
matter of domain name registrars (InterNIC, national NICs), reverse domain
name delegation is being done by the authorities, assigning IP address
space - Internet service providers and regional Internet registries (see
the answer to "How do I get my address assigned from the NIC?" in this

Important notes:

(1) If you're assigned a block or one or more "Class C" networks, you'll
have to maintain a separate reverse domain zone file for each "Class C"
from the block. For example, if you're assigned 10.91.8/22, you'll have to
configure a separate zone file for 4 domains:

and to delegate them further in the DNS (according to the advice from your

(2) If you're assigned a whole "B class" (say, 10.91/16), you're in charge
for the whole 91.10.IN-ADDR.ARPA zone. See the answer to "How do I subnet
a Class B Address?" in the CONFIGURATION section.

(3) If you're assigned only a portion of a "C class" (say,
see the answer to "Subnetted domain name service" question in the

For more information on reverse domain delegations see:

* : /apnic/docs/in-addr-request


Question 2.14.  How do I get my address assigned from the NIC ?

Date: Mon Jun 15 22:48:24 EDT 1998

IP address space assignment to end users is no longer being performed by
regional Internet registries (InterNIC, ARIN, RIPE NCC, APNIC).   If you
need IP address space, you should make a request to your Internet service
provider.  If you already have address space and need more IP numbers,
make a request to your ISP again and you may be given more numbers
(different ISPs have different allocation requirements and procedures).
If you are a smaller ISP - talk to your upstream ISP to obtain necessary
numbers for your customers.  If you change the ISP in the future, you MAY
have to renumber your network.  See RFC 2050 and RFC 2071 for more
information on this issue.

Currently, address space is being distributed in a hierarchical manner:
ISPs assign addresses to their end customers. The regional Internet
registries allocate blocks of addresses (usually sized between /19  (32 "C
class") and /16 (a "B class")) to the ISPs.  Finally - IANA  (Internet
Assigned Number Authority) allocates necessary address space (/8 ("A
class") sized blocks) to the regional registries, as the need for  address
space arises. This hierarchical process ensures more efficient  routing on
the backbones (less traffic caused by routing information  updates, better
memory utilization in backbone routers etc.) as well as  more rational
address usage.

If you are an ISP, planning to connect yourself to more than one ISP (i.e.
becoming multi-homed) and/or expecting to have a lot of customers, you'll
have to obtain ISP independent address space from a regional Internet
registry. Depending on your geographical locations, you can obtain such
address blocks (/19 and larger blocks) from:

* RIPE NCC ( -> Europe, North Africa and Middle East
* ARIN ( -> North and South America, Central Africa
* APNIC ( -> Asian and Pacific region

While the regional registries do not sell address space, they do charge
for their services (allocation of address space, reverse domain
delegations etc.)


Question 2.15.  Is there a block of private IP addresses I can use?

Date: Sun May  5 23:02:49 EDT 1996

Yes there is.  Please refer to RFC 1918:

   1918 Address Allocation for Private Internets. Y. Rekhter, B.
        Moskowitz, D. Karrenberg, G. de Groot, & E. Lear. February 1996.
        (Format: TXT=22270 bytes)
RFC 1918 documents the allocation of the following addresses for use by
``private internets'':        -      -     -


Question 2.16.  Does BIND cache negative answers (failed DNS lookups) ?

Date: Mon Jan  2 13:55:50 EST 1995

Yes, BIND 4.9.3 and more recent versions will cache negative answers.


Question 2.17.  What does an NS record really do ?

Date: Wed Jan 14 12:28:46 EST 1998

The NS records in your zone data file pointing to the zone's name  servers
(as opposed to the servers of delegated subdomains) don't do  much.
They're essentially unused, though they are returned in the  authority
section of reply packets from your name servers.

However, the NS records in the zone file of the parent domain are used to
find the right servers to query for the zone in question.  These records
are more important than the records in the zone itself.

However, if the parent domain server is a secondary or stub server for the
child domain, it will "hoist" the NS records from the child into the
parent domain.  This frequently happens with reverse domains, since the
ISP operates primary reverse DNS for its CIDR block and also often runs
secondary DNS for many customers' reverse domains.

Caching servers will often replace the NS records learned from the parent
server with the authoritative list that the child server sends in its
authority section.  If the authoritative list is missing the secondary
servers, those caching servers won't be able to look up in this domain if
the primary goes down.

After all of this, it is important that your NS records be correct !


Question 2.18.  DNS ports

Date: Wed Jan 14 12:31:39 EST 1998

The following table shows what TCP/UDP ports bind before 8.x DNS uses to
send and receive queries:

   Prot Src   Dst   Use
   udp  53    53    Queries between servers (eg, recursive queries)
                    Replies to above
   tcp  53    53    Queries with long replies between servers, zone 
                    transfers Replies to above
   udp  >1023 53    Client queries (sendmail, nslookup, etc ...)
   udp  53    >1023 Replies to above
   tcp  >1023 53    Client queries with long replies
   tcp  53    >1023 Replies to above

   Note: >1023 is for non-priv ports on Un*x clients. On other client 
         types, the limit may be more or less.

BIND 8.x no longer uses port 53 as the source port for recursive queries.
By defalt it uses a random port >1023, although you can configure a
specific port (53 if you want).

Another point to keep in mind when designing filters for DNS is that a DNS
server uses port 53 both as the source and destination for its queries.
So, a client queries an initial server from an unreserved port number to
UDP port 53.  If the server needs to query another server to get the
required info, it sends a UDP query to that server with both source and
destination ports set to 53.  The response is then sent with the same
src=53 dest=53 to the first server which then responds to the original
client from port 53 to the original source port number.

The point of all this is that putting in filters to only allow UDP between
a high port and port 53 will not work correctly, you must also allow the
port 53 to port 53 UDP to get through.

Also, ALL versions of BIND use TCP for queries in some cases.  The
original query is tried using UDP.  If the response is longer than the
allocated buffer, the resolver will retry the query using a TCP
connection.  If you block access to TCP port 53 as suggested above, you
may find that some things don't work.

Newer version of BIND allow you to configure a list of IP addresses from
which to allow zone transfers.  This mechanism can be used to prevent
people from outside downloading your entire namespace.


Question 2.19.  What is the cache file

Date: Fri Dec  6 01:15:22 EST 1996

From the "Name Server Operations Guide"

      6.3.  Cache Initialization
         6.3.1.  root.cache
                 The name server needs to know the servers that
            are  the  authoritative  name  servers for the root
            domain of the network.  To do this we have to prime
            the name server's cache with the addresses of these
            higher authorities.  The location of this  file  is
            specified  in  the  boot  file. ...


Question 2.20.  Obtaining the latest cache file

Date: Fri Dec  6 01:15:22 EST 1996

If you have a version of dig running, you may obtain the information with
the command

      dig . ns

A perl script to handle some possible problems when using this method
from behind a firewall and that can also be used to periodically obtain
the latest cache file was posted to  during
early October, 1996.  It was posted with the subject "Keeping  db.cache
current". It is available at

The latest cache file may also be obtained from the InterNIC via ftp  or

      ;       This file is made available by InterNIC registration services
      ;       under anonymous FTP as
      ;           file                /domain/named.root
      ;           on server           FTP.RS.INTERNIC.NET
      ;       -OR- under Gopher at    RS.INTERNIC.NET
      ;           under menu          InterNIC Registration Services (NSI)
      ;              submenu          InterNIC Registration Archives
      ;           file                named.root


Question 2.21.  Selecting a nameserver/root cache

Date: Mon Aug  5 22:54:11 EDT 1996

Exactly how is the a root server selected from the root cache? Does the
resolver attempt to pick the closest host or is it random or is it via
sortlist-type workings?  If the root server selected is not available (for
whatever reason), will the the query fail instead of attempting another
root server in the list ?

Every recursive BIND name server (that is, one which is willing to go out
and find something for you if you ask it something it doesn't know) will
remember the measured round trip time to each server it sends queries to.
If it has a choice of several servers for some domain (like "." for
example) it will use the one whose measured RTT is lowest.

Since the measured RTT of all NS RRs starts at zero (0), every one gets
tried one time.  Once all have responded, all RTT's will be nonzero, and
the "fastest server" will get all queries henceforth, until it slows down
for some reason.

To promote dispersion and good record keeping, BIND will penalize the RTT
by a little bit each time a server is reused, and it will penalize the RTT
a _lot_ if it ever has to retransmit a query.  For a server to stay "#1",
it has to keep on answering quickly and consistently.

Note that this is something BIND does that the DNS Specification does not
mention at all.  So other servers, those not based on BIND, might behave
very differently.


Question 2.22.  Domain names and legal issues

Date: Mon Jun 15 22:15:32 EDT 1998

A domain name may be someone's trademark and the use of a trademark
without its owner's permission may be a trademark violation.  This may
lead to a  legal dispute.  RFC 1591 allows registration authorities to
play a neutral role in domain name disputes, stating that:

     In case of a dispute between domain name registrants as to the
     rights to a particular name, the registration authority shall have
     no role or responsibility other than to provide the contact
     information to both parties.

The InterNIC's current domain dispute policy (effective February 25, 1998)
is located at:

Other domain registrars have similar domain dispute policies.

The following information was submitted by Carl Oppedahl
<> :

If the jealous party happens to have a trademark registration, it is quite
likely that the domain name owner will lose the domain name, even if they
aren't infringing the trademark.  This presents a substantial risk of loss
of a domain name on only 30 days' notice.  Anyone who is the manager of an
Internet-connected site should be aware of this risk and should plan for

See "How do I protect myself from loss of my domain name?" at

For an example of an ISP's battle to keep its domain name, see

A compendium of information on the subject may be found at


Question 2.23.  Iterative and Recursive lookups

Date: Wed Jul  9 22:05:32 EDT 1997

Q: What is the difference between iterative and recursive lookups ?  How
do you configure them and when would you specify one over the other ?

A: (from an answer written by Barry Margolin) In an iterative lookup, the
server tells the client "I don't know the answer, try asking <list of
other servers>".  In a recursive lookup, the server asks one of the other
servers on your behalf, and then relays the answer back to you.

Recursive servers are usually used by stub resolvers (the name lookup
software on end systems).  They're configured to ask a specific set of
servers, and expect those servers to return an answer rather than a
referral.  By configuring the servers with recursion, they will cache
answers so that if two clients try to look up the same thing it won't have
to ask the remote server twice, thus speeding things up.

Servers that aren't intended for use by stub resolvers (e.g. the root
servers, authoritative servers for domains).  Disabling recursion reduces
the load on them.

In BIND 4.x, you disable recursion with "options no-recursion" in the
named.boot file.


Question 2.24.  Dynamic DNS

Mon Jan 18 20:31:58 EST 1999

Q: Bind 8 includes some support for Dynamic DNS as specified in  RFC 2136.
It does not currently include the authentication mechanism that is
described in RFC 2137, meaning that any update requests received from
allowed hosts will be honored.

Could someone give me a working example of what syntax nsupdate expects ?
Is it possible to write an update routine which directs it's update to a
particular server, ignoring what the DNS servers are the serving NS's?

A: You might check out Michael Fuhr's Net::DNS Perl module, which you can
use to put together dynamic update requests.  See for additional information.
Michael posted a sample script to show how to use Net::DNS:

     #!/usr/local/bin/perl -w
     use Net::DNS;
     $res = new Net::DNS::Resolver;
     $update = new Net::DNS::Update("");
     $update->push("update", rr_del(""));
     $update->push("update", rr_add(" A"));
     $ans = $res->send($update);
     print $ans ? $ans->header->rcode : $res->errorstring, "\n";

Additional information for Dynamic DNS updates may be found at


Question 2.25.  What version of bind is running on a server ?

Date: Mon Mar  9 22:15:11 EST 1998

On 4.9+ servers, you may obtain the version of bind running with the
following command:

dig txt chaos version.bind.

and optionally pipe that into 'grep VERSION'.  Please note that this will
not work on an older nameserver.


Question 2.26.  BIND and Y2K

Date: Thu Feb 11 14:58:04 EST 1999

Is the "Y2K" problem an issue for bind ?

You will find the Internet Software Consortium's comment on the "Y2K"
issue at


Section 3.  UTILITIES

 Q3.1        Utilities to administer DNS zone files
 Q3.2        DIG - Domain Internet Groper
 Q3.3        DNS packet analyzer
 Q3.4        host
 Q3.5        How can I use DNS information in my program?
 Q3.6        A source of information relating to DNS


Question 3.1.  Utilities to administer DNS zone files

Date: Tue Jan  7 00:22:31 EST 1997

There are a few utilities available to ease the administration of zone
files in the DNS.

Two common ones are h2n and makezones.  Both are perl scripts.  h2n is
used to convert host tables into zone data files.  It is available for
anonymous ftp from : /published/oreilly/nutshell/dnsbind/dns.tar.Z

makezones works from a single file that looks like a forward zone file,
with some additional syntax for special cases.  It is included in the
current BIND distribution.  The newest version is always available for
anonymous ftp from : /pub/software/programs/DNS/makezones

bpp is a m4 macro package for pre-processing the master files bind uses to
define zones.   Information on this package may be found at

More information on various DNS related utilities may be found using the
DNS Resources Directory


Question 3.2.  DIG - Domain Internet Groper

Date: Thu Dec  1 11:09:11 EST 1994

The latest and greatest, official, accept-no-substitutes version of the
Domain Internet Groper (DiG) is the one that comes with BIND.   Get the
latest kit.


Question 3.3.  DNS packet analyzer

Date: Mon Jun 15 21:42:11 EDT 1998

There is a free ethernet analyzer called Ethload available for PC's
running DOS. The latest filename is ETHLD200.ZIP. It understands lots  of
protocols including TCP/UDP. It'll look inside there and display
DNS/BOOTP/ICMP packets etc. (Ed. note: something nice for someone to add
to tcpdump ;^) ).  Depending on the ethernet controller it's given  it'll
perform slightly differently. It handles NDIS/Novell/Packet  drivers.  It
works best with Novell's promiscuous mode drivers.   The current home page
for Ethload is


Question 3.4.  host

Date: Thu Feb 11 14:43:39 EST 1999

A section from the host man page:

     host looks for information about Internet hosts and domain
     names.  It gets this information from a set of intercon-
     nected servers that are spread across the world. The infor-
     mation is stored in the form of "resource records" belonging
     to hierarchically organized "zones".

     By default, the program simply converts between host names
     and Internet addresses. However, with the -t, -a and -v
     options, it can be used to find all of the information about
     domain names that is maintained by the domain nameserver
     system.  The information printed consists of various fields
     of the associated resource records that were retrieved.

     The arguments can be either host names (domain names) or
     numeric Internet addresses.

'host' is compatible with both BIND 4.9 and BIND 4.8

'host' may be found in contrib/host in the BIND distribution.  The latest
version always available for anonymous ftp from : /pub/network/host.tar.Z

It may also be found for anonymous ftp from : /networking/ip/dns/host.tar.Z

Programs with some of the functionality of host for NT may be found at under "Network Tools, DNS Lookup Utilities".


Question 3.5.  How can I use DNS information in my program?

Date: Fri Feb 10 15:25:11 EST 1995

It depends on precisely what you want to do:

* Consider whether you need to write a program at all.  It may well be
  easier to write a shell program (e.g. using awk or perl) to parse the
  output of dig, host or nslookup.
* If all you need is names and addresses, there will probably be system
  routines 'gethostbyname' and 'gethostbyaddr' to provide this
* If you need more details, then there are system routines (res_query and
  res_search) to assist with making and sending DNS queries.  However,
  these do not include a routine to parse the resulting answer (although
  routines to assist in this task are provided).  There is a separate
  library available that will take a DNS response and unpick it into its
  constituent parts, returning a C structure that can be used by the
  program.  The source for this library is available for anonymous ftp at : /hpux/Networking/Admin/resparse-1.2


Question 3.6.  A source of information relating to DNS

Mon Jan 18 20:35:49 EST 1999

You may find utilities and tools to help you manage your zone files
(including WWW front-ends) in the "tools" section of the DNS  resources

Two that come to mind are MIT's WebDNS and the University of Utah tools.

There are also a number of commercial IP management tools available.  Data
Communications had an article on the subject in Sept/Oct of 1996.  The
tools mentioned in the article and a few others may be found at the
following sites:

* IP Address management,
* IP-Track,
* NetID,
* QIP,
* UName-It,
* dnsboss,



 Q4.1        TCP/IP Host Naming Conventions
 Q4.2        What are slaves and forwarders ?
 Q4.3        When is a server authoritative?
 Q4.4        My server does not consider itself authoritative !
 Q4.5        NS records don't configure servers as authoritative ?
 Q4.6        underscore in host-/domainnames
 Q4.7        How do I turn the "_" check off ?
 Q4.8        What is lame delegation ?
 Q4.9        How can I see if the server is "lame" ?
 Q4.10       What does opt-class field in a zone file do?
 Q4.11       Top level domains
 Q4.12       US Domain
 Q4.13       Classes of networks
 Q4.14       What is CIDR ?
 Q4.15       What is the rule for glue ?
 Q4.16       What is a stub record/directive ?


Question 4.1.  TCP/IP Host Naming Conventions

Date: Mon Aug  5 22:49:46 EDT 1996

One guide that may be used when naming hosts is RFC 1178, "Choosing a Name
for Your Computer", which is available via anonymous FTP from : /rfc/rfc1178.txt

RFCs (Request For Comments) are specifications and guidelines for how many
aspects of TCP/IP and the Internet (should) work.  Most RFCs are fairly
technical documents, and some have semantics that are hotly contested in
the newsgroups.  But a few, like RFC 1178, are actually good to read for
someone who's just starting along a TCP/IP path.


Question 4.2.  What are slaves and forwarders ?

Date: Mon Jan 18 22:14:30 EST 1999

Parts of this section were contributed by Albert E. Whale.

"forwarders" is a list of NS records that are _prepended_ to a list of NS
records to query if the data is not available locally.  This allows a rich
cache of records to be built up at a centralized location.  This is good
for sites that have sporadic or very slow connections to the Internet.
(demand dial-up, for example)  It's also just a good idea for very large
distributed sites to increase the chance that you don't have to go off to
the Internet to get an IP address. (sometimes for addresses across the

If you have a "forwarders" line, you will only consult the root servers if
you get no response from the forwarder.  If you get a response, and it
says there's no such host, you'll return that answer to the client -- you
won't consult the root.

The "forwarders" statement is found in the /etc/named.boot file which is
read each time DNS is started.  The command format is as follows:

forwarders <IP Address #1> [<IP Address #2>, .... <IP Address #n>]
The "forwarders" line specifies the IP Address(es) of DNS servers that
accept queries from other servers.

The "forwarders" command is used to cause a large site wide cache to be
created on a master and reduce traffic over the network to other servers.
It can also be used to allow DNS servers to answer Internet name queries
which do not have direct access to the Internet.

The forwarders command is used in conjunction with the traditional DNS
configuration which requires that a NS entry be found in the cache file.
The DNS server can support the forwarders command if the server is able to
resolve entries that are not part of the local server's cache.

"slave" modifies this to say to replace the list of NS records with the
forwarders entry, instead of prepending to it.  This is for firewalled
environments, where the nameserver can't directly get out to the Internet
at all.

"slave" is meaningless (and invalid, in late-model BINDs) without
"forwarders".  "forwarders" is an entry in named.boot, and therefore
applies only to the nameserver (not to resolvers).

The "slave" command is usually found immediately following the forwarders
command in the boot file.  It is normally used on machines that are
running DNS but do not have direct access to the Internet.  By using the
"forwarders" and "slave" commands the server can contact another DNS
server which can answer DNS queries.  The "slave" option may also be used
behind a firewall where there may not be a network path available to
directly contact nameservers listed in the cache.

Additional information on slave servers may be found in the BOG (BIND
Operations Guide section 6.1.8 (Slave


Question 4.3.  When is a server authoritative?

Date: Mon Jan  2 13:15:13 EST 1995

In the case of BIND:

* The server contains current data in files for the zone in question (Data
  must be current for secondaries, as defined in the SOA)
* The server is told that it is authoritative for the zone, by a 'primary'
  or 'secondary' keyword in /etc/named.boot.
* The server does an error-free load of the zone.


Question 4.4.  My server does not consider itself authoritative !

Date: Mon Jan  2 13:15:13 EST 1995

The question was:

  What if I have set up a DNS where there is an SOA record for
  the domain, but the server still does not consider itself
  authoritative.  (when using nslookup and set server=the correct machine.)
  It seems that something is not matching up somewhere.  I suspect
  that this is because the service provider has not given us control
  over the IP numbers in our own domain, and so while the machine listed
  has an A record for an address, there is no corresponding PTR record.

With the answer:

  That's possible too, but is unrelated to the first question.
  You need to be delegated a zone before outside people will start
  talking to your server.  However, a server can still be authoritative
  for a zone even though it hasn't been delegated authority (it's just 
  that only the people who use that as their server will see the data).
  A server may consider itself non-authoritative even though it's a
  primary if there is a syntax error in the zone (see the list in the 
  previous question).


Question 4.5.  NS records don't configure servers as authoritative ?

Date: Fri Dec  6 16:13:34 EST 1996

Nope, delegation is a separate issue from authoritativeness.  You can
still be authoritative, but not delegated.  (you can also be  delegated,
but not authoritative -- that's a "lame delegation")


Question 4.6.  underscore in host-/domainnames

Date: Sat Aug  9 20:30:37 EDT 1997

The question is "Are underscores are allowed in host- or domainnames" ?
        RFC 1033 allows them.
        RFC 1035 doesn't.
        RFC 1123 doesn't.
        dnswalk complains about them.

Which RFC is the final authority these days?

Actually RFC 1035 deals with names of machines or names of mail domains.
i.e "_" is not permitted in a hostname or on the RHS of the "@" in

Underscore is permitted where ever the domain is NOT one of these types
of addresses.

In general the DNS mostly contains hostnames and mail domainnames.  This
will change as new resource record types for authenticating DNS  queries
start to appear.

The latest version of 'host' checks for illegal characters in A/MX record
names and the NS/MX target names.

After saying all of that, remember that RFC 1123 is a Required Internet
Standard (per RFC 1720), and RFC 1033 isn't.  Even  RFC 1035 isn't a
required standard.  Therefore, RFC 1123 wins, no contest.

From RFC 1123, Section 2.1

   2.1  Host Names and Numbers

      The syntax of a legal Internet host name was specified in RFC-952
      [DNS:4].  One aspect of host name syntax is hereby changed: the
      restriction on the first character is relaxed to allow either a
      letter or a digit.  Host software MUST support this more liberal

   And described by Dave Barr in RFC1912:

      Allowable characters in a label for a host name are only ASCII
      letters, digits, and the `-' character.  Labels may not be all
      numbers, but may have a leading digit  (e.g.,  Labels must
      end and begin only with a letter or digit.  See [RFC 1035] and [RFC
      1123].  (Labels were initially restricted in [RFC 1035] to start with
      a letter, and some older hosts still reportedly have problems with
      the relaxation in [RFC 1123].)  Note there are some Internet
      hostnames which violate this rule (,

Finally, one more piece of information (From Paul Vixie):

   RFC 1034 says only that domain names have characters in them, though it
   says so with enough fancy and indirection that it's hard to tell exactly.

   Generally, for second level domains (i.e., something you would get from
   InterNIC or from the US Domain Registrar and probably other ISO 3166
   country code TLDs), RFC 952 is thought to apply.  RFC 952 was about host
   names rather than domain names, but the rules seemed good enough.

        <domainname> ::= <hname>

        <hname> ::= <name>*["."<name>]
	<name>  ::= <let>[*[<let-or-digit-or-hyphen>]<let-or-digit>]
There has been a recent update on this subject which may be found in : /internet-drafts/draft-andrews-dns-hostnames-03.txt.

An RFC Internet standards track protocol on the subject "Clarifications to
the DNS Specification" may be found in RFC 2181.  This updates RFC 1034,
RFC 1035, and RFC 1123.


Question 4.7.  How do I turn the "_" check off ?

Date: Mon Nov 10 22:54:54 EST 1997

In the 4.9.5-REL and greater, you may turn this feature off with the
option "check-names" in the named boot file.  This option is documented
in the named manual page.  The syntax is:

   check-names primary warn


Question 4.8.  What is lame delegation ?

Date: Tue Mar 11 21:51:21 EST 1997

Two things are required for a lame delegation:

* A nameserver X is delegated as authoritative for a zone.
* Nameserver X is not performing nameservice for that zone.

Try to think of a lame delegation as a long-term condition, brought about
by a misconfiguration somewhere.  Bryan Beecher's 1992 LISA paper on lame
delegations is good to read on this.  The problem really lies in
misconfigured nameservers, not "lameness" brought about by transient
outages.  The latter is common on the Internet and hard to avoid, while
the former is correctable.

In order to be performing nameservice for a zone, it must have (presumed
correct) data for that zone, and it must be answering authoritatively to
resolver queries for that zone.  (The AA bit is set in the flags section)

The "classic" lame delegation case is when nameserver X is delegated as
authoritative for domain Y, yet when you ask X about Y, it returns
non-authoritative data.

Here's an example that shows what happens most often (using dig, dnswalk,
and doc to find).

Let's say the domain gets registered at the NIC and they have
listed 2 primary name servers, both from their *upstream* provider:      IN      NS      IN      NS      IN      NS

So the root servers have this info.  But when the admins at
actually set up their zone files they put something like:      IN      NS      IN      NS

So your name server may have the nameserver info cached (which it may have
gotten from the root).  The root says "go ask" since they are

This is usually from stuff being registered at the NIC (either
or, and then updated later, but the folks who make the
updates later never let the folks at the NIC know about it.


Question 4.9.  How can I see if the server is "lame" ?

Date: Mon Sep 14 22:09:35 EDT 1998

Go to the authoritative servers one level up, and ask them who they think
is authoritative, and then go ask each one of those delegees if they think
that they themselves are authoritative.  If any responds "no", then you
know who the lame delegation is, and who is delegating lamely to them.
You can then send off a message to the administrators of the level above.

The 'lamers' script from Byran Beecher really takes care of all this for
you.  It parses the lame delegation notices from BIND's syslog and
summarizes them for you.  It may be found in the contrib section of the
latest BIND distribution.  The latest version is included in  the BIND

If you want to actively check for lame delegations, you can use 'doc' and
'dnswalk'.   You can check things manually with 'dig'.

The InterNIC recently announced a new lame delegation that will be in
effect on 01 October, 1996.  Here is a summary:

* After receipt/processing of a name registration template, and at random
  intervals thereafter, the InterNIC will perform a DNS query  via UDP
  Port 53 on domain names for an SOA response for the name  being
* If the query of the domain name returns a non-authoritative response
  from all the listed name servers, the query will be repeated four times
  over the next 30 days at random intervals approximately 7 days apart,
  with notification to all listed whois and nameserver contacts of the
  possible pending deletion.  If at least one server answers correctly,
  but one or more are lame, FYI notifications will be sent to all contacts
  and checking will be discontinued.  Additionally, e-mail notices will be
  provided to the contact for the name servers holding the delegation to
  alert them to the "lame" condition.  Notifications will state explicitly
  the consequences of not correcting the "lame" condition and will be
  assigned a descriptive subject as follows:

     Subject: Lame Delegation Notice: DOMAIN_NAME

  The notification will include a timestamp for when the query was
* If, following 30 days, the name servers still provide no SOA response,
  the name will be placed in a "hold" status and the DNS information will
  no longer be propagated.  The administrative contact will be notified by
  postal mail and all whois contacts will be notified by e-mail, with
  instructions for taking corrective action.
* Following 60 days in a "hold" status, the name will be deleted and made
  available for re-registration.  Notification of the final deletion will
  be sent to the name server and domain name contacts  listed in the NIC


Question 4.10.  What does opt-class field in a zone file do?

Date: Thu Dec  1 11:10:39 EST 1994

This field is the address class.  From the BOG - the address class; currently, only one class
      is supported: IN  for  internet  addresses  and  other
      internet information.  Limited support is included for
      the HS  class,  which  is  for  MIT/Athena  ``Hesiod''


Question 4.11.  Top level domains

Date: Mon Jun 15 22:25:57 EDT 1998

RFC 1591 defines the term "Top Level Domain" (TLD) as:

   2.  The Top Level Structure of the Domain Names

   In the Domain Name System (DNS) naming of computers there is a
   hierarchy of names.  The root of system is unnamed.  There are a set
   of what are called "top-level domain names" (TLDs).  These are the
   generic TLDs (EDU, COM, NET, ORG, GOV, MIL, and INT), and the two
   letter country codes from ISO-3166.  It is extremely unlikely that
   any other TLDs will be created.

The unnamed root-level domain (usually denoted as ".") is currently being
maintained by the Internet Assigned Number Authority (IANA). Beside that,
IANA is currently in charge for some other vital functions on the Internet
today, including global distribution of address space, autonomous system
numbers and all other similar numerical constants, necessary for proper
TCP/IP protocol stack operation (e.g. port numbers, protocol identifiers
and so on). According to the recent proposals of the US Government, better
known as "Green Paper":

IANA will gradually transfer its current functions to a new non-profit
international organization, which won't be influenced exclusively by the
US Government. This transfer will occur upon the final version of the
"Green Paper" has been issued.

Currently, the root zone contains five categories of top level domains:

(1) World wide gTLDs - maintained by the InterNIC:
    - COM - Intended for commercial entities - companies, corporations etc.
    - NET - Intended for Internet service providers and similar entities.
    - ORG - Intended for other organizations, which don't fit to the above.

(2) Special status gTLDs
    - EDU - Restricted to 4 year colleges and universities only.
    - INT - Intended for international treaties and infrastructural databases.

(3) US restricted gTLDs
    - GOV - Intended for US Government offices and agencies.
    - MIL - Intended for the US military.

(4) ISO 3166 country code TLDs (ccTLDs) - FR, CH, SE etc.

(5) Reverse TLD - IN-ADDR.ARPA.

Generic TLDs COM, NET, ORG and EDU are currently being maintained by the
InterNIC. IANA maintains INT and IN-ADDR.ARPA. The US Government and US
Army maintain their TLDs independently.

The application form for the EDU, COM, NET, ORG, and  GOV domains may be
found for anonymous ftp from: : /templates/domain-template.txt

The country code domains (ISO 3166 based - example, FR, NL, KR, US) are
each organized by an administrator for that country. These  administrators
may further delegate the management of portions of the naming tree. These
administrators are performing a public service on behalf of the Internet
community.  The ISO-3166 country codes may be found for anonymous ftp

* : /in-notes/iana/assignments/country-codes
* : /iso3166-codes

More information about particular country code TLDs may be found at:

* http://www.UNINETT.NO/navn/domreg.html
* : /pub/whois/whois-servers.list

Contrary to the initial plans, stated in the RFC 1591, not to  include
more TLDs in the near future, some other forums don't share that  opinion.

The International Ad Hoc Committee (IAHC) ({ was was
selected by the IAB, IANA, ITU, INTA, WIPO, and ISOC to study and
recommend changes to the existing Domain Name System (DNS).  The IAHC
recommended the following regarding TLD's on February 4, 1997:

     In order to cope with the great and growing demand for Internet
     addresses in the generic top level domains, the generic Top Level
     Domain (gTLD) MoU calls for the establishment of seven new gTLDs in
     addition to the existing three. These will be .FIRM, .STORE, .WEB,
     .ARTS, .REC, .NOM and .INFO. In addition, the MoU provides for the
     setting up of an initial 28 new registrars around the world four
     from each of seven world regions. More registrars will be added as
     operational and administrative issues are worked out. Registrars
     will compete on a global basis, and users will be able shop around
     for the registrar which offers them the best arrangement and price.
     Users will also be able to change registrar at any time while
     retaining the same domain address, thus ensuring global portability.

The full text of the recommendation may be found at:

Beside IAHC, several other forums have been created, by people willing to
change the current addressing structure in the global network. Some of
them may be found at:


You may participate in one of the discussions on iTLD proposals at

* To sign up:
* Old postings:


Question 4.12.  US Domain

Date: Mon Jun 15 22:25:57 EDT 1998

Information on the US domain registration services may be found at

The application form for the US domain may be found:

* for anonymous ftp from : /templates/us-domain-template.txt

A WWW interface to a whois server for the US domain may be found at  This whois server may be
used with the command
   % whois -h
   % whois
  (depending on your version of whois).  


Question 4.13.  Classes of networks

Date: Sun Feb  9 22:36:21 EST 1997

The usage of 'classes of networks' (class A, B, C) are historical and have
been replaced by CIDR blocks on the Internet.  That being said...

An Internet Protocol (IP) address is 32 bit in length, divided into  two
or three parts (the network address, the subnet address (if present), and
the host address.  The subnet addresses are only present if the network
has been divided into subnetworks.  The length of the network, subnet, and
host field are all variable.

There are five different network classes.  The leftmost bits indicate  the
class of the network.

       # of     # of
      bits in  bits in
      network   host
Class  field    field   Internet Protocol address in binary  Ranges
  A      7       24      0NNNNNNN.HHHHHHHH.HHHHHHHH.HHHHHHHH    1-127.x.x.x
  B     14       16      10NNNNNN.NNNNNNNN.HHHHHHHH.HHHHHHHH  128-191.x.x.x
  C     21        8      110NNNNN.NNNNNNNN.NNNNNNNN.HHHHHHHH  192-223.x.x.x
  D     NOTE 1           1110xxxx.xxxxxxxx.xxxxxxxx.xxxxxxxx  224-239.x.x.x
  E     NOTE 2           11110xxx.xxxxxxxx.xxxxxxxx.xxxxxxxx  240-247.x.x.x

   where N represents part of the network address and H represents part of 
   the host address.   When the subnet address is defined, the needed bits 
   are assigned from the host address space.

   NOTE 1: Reserved for multicast groups - RFC 1112
   NOTE 2: Reserved for future use is reserved for local loopback.


Question 4.14.  What is CIDR ?

Date: Tue Nov  5 23:47:29 EST 1996

CIDR is "Classless Inter-Domain Routing (CIDR).  From RFC 1517:

      ...Classless Inter-Domain Routing (CIDR) attempts to deal with
      these problems by defining a mechanism to slow the growth of 
      routing tables and reduce the need to allocate new IP network 

Much more information may be obtained in RFCs 1467, 1517, 1518, 1520;
with primary reference 1519.

Also please see the CIDR FAQ at



Question 4.15.  What is the rule for glue ?

Date: Mon Sep 14 22:04:42 EDT 1998

A glue record is an A record for a name that appears on the right-hand
side of a NS record.  So, if you have this:

        IN      NS    IN      A

then the second record is a glue record (for the NS record above it).

You need glue records when -- and only when -- you are delegating
authority to a nameserver that "lives" in the domain you are delegating
*and* you aren't a secondary server for that domain.

In other words, in the example above, you need to add an A record for since it "lives" in the domain it serves.  This boot
strapping information is necessary:  How are you supposed to find out the
IP address of the nameserver for domain FOO if the nameserver for FOO
"lives" in FOO?

If you have this NS record:         IN      NS

you do NOT need a glue record, and, in fact, adding one is a very bad
idea.  If you add one, and then the folks at change the
address, then you will be passing out incorrect data.

Also, unless you actually have a machine called something.IN-ADDR.ARPA,
you will never have any glue records present in any of your "reverse"

There is also a sort of implicit glue record that can be useful (or
confusing :^) ).  If the parent server ( domain in example
above) is a secondary server for the child, then the A record will be
fetched from the child server when the zone transfer is done.  The glue is
still there but it's a little different, it's in the ip address in  the
named.boot line instead of explicitly in the data.  In this case  you can
leave out the explicit glue A record and leave the manually  configured
"glue" in just the one place in the named.boot file.

RFC 1537 says it quite nicely:

      2. Glue records
         Quite often, people put unnecessary glue (A) records in their 
         zone files. Even worse is that I've even seen *wrong* glue records 
         for an external host in a primary zone file! Glue records need only 
         be in a zone file if the server host is within the zone and there 
         is no A record for that host elsewhere in the zone file.
         Old BIND versions ("native" 4.8.3 and older versions) showed the
         problem that wrong glue records could enter secondary servers in
         a zone transfer.

In response to a question on glue records,  Mark Andrews stated the

        BIND's current position is somewhere between the overly restrictive
        position given above and the general allow all glue position that 
        prevailed in 4.8.x.

        BIND's current break point is below the *parent* zone, i.e. it
        allows glue records from sibling zones of the zone being

        The following applies for glue

            Below child: always required
            Below parent: often required
            Elsewhere: seldom required

        The main reason for resticting glue is not that it in not
        required but that it is impossible to track down *bad* glue if
        you allow glue that falls into "elsewhere".  Ask UUNET or any
        other large provider the problems that BIND 4.8.x general glue
        rules caused.  If you want to examine a true data virus you need
        only look at the A records for

        The "below parent" and "below child" both allow you to find bad
        glue records.  Below the parent has a bigger search space to that
        of below the child but is still managable.

        It is believed that the elsewhere cases are sufficiently rare
        that they can be ignored in practice and if detected can be worked
        around by creating be creating A records for the nameservers
        that fall into one of the other two cases.  This requires
        resolvers to correctly lookup missing glue and requery when they
        have this glue.  BIND does *not* do this correctly at present.

Question 4.16.  What is a stub record/directive ?

Date: Mon Nov 10 22:45:33 EST 1997

Q: What is the difference, or advantages, of using a stub record  versus
using an NS record and a glue record in the zone file?

Cricket Liu responds,

   "Stub" is a directive, not a record (well, it's a directive in BIND 4;
in BIND 8, it's an option to the "zone" statement).  The stub    directive
configures your name server to do a zone transfer just as a    secondary
master name server would, but to use just the NS records.     It's a
convenient way for a parent name server to keep track of the    servers
for subzones.

and Barry Margolin adds,

   Using stub records ensures that the NS records in the parent will be
consistent with the NS records in the child.  If you have to enter NS
records manually, you run the possibility that the child will change his
servers without telling you.  Then you'll give out incorrect delegation
information, possibly resulting in the infamous "lame delegation".

The remainder of the FAQ is in the next part (Part 2 of 2).

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