Procedures for DNS Delegation in the IN-ADDR.ARPA Domain

[Daniel Karrenberg <]

                    European Internet Registry:

                   Procedures for DNS Delegation

                     in the IN-ADDR.ARPA Domain



                         Daniel Karrenberg
                          Marten Terpstra

                           November  1993

                        Document-ID: ripe-zz
                         Obsoletes: ripe-85




                              ABSTRACT

           This document describes the procedures for the
      delegation of zones in European subdomains of
      IN-ADDR.ARPA.



Introduction


The domain tree below IN-ADDR.ARPA is used to facilitate "reverse"
mapping from IP addresses to domain names [RFC883, RFC1033].  This
document describes the procedures for the delegation of zones in
European subdomains of IN-ADDR.ARPA.


Randomly Assigned Numbers


There are two groups of European network numbers: hierarchically
assigned numbers and randomly assigned ones. The hierarchically
assigned numbers are part of the 193.x.y.0 and 194.x.y.0 network
blocks. All other network numbers, class A, class B and 192.x.y.0
class Cs are randomly assigned.

Subdomains of IN-ADDR.ARPA describing reverse mappings for randomly
assigned networks have to be handled globally and are handled by the
InterNIC hostmaster@localhost.






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Hierarchically Assigned Numbers

The subdomains of IN-ADDR.ARPA corresponding to the hierarchically
assigned network numbers are administered by the RIPE NCC.  These
network numbers currently are


        193.0.0.0 - 194.255.255.0


Although the procedures described below refer to the 193.x.y block
of addresses, for clarity they apply to all such blocks.


With the assignment of class C network numbers following RFC1466,
large chunks of the address space are delegated to regional Internet
Registries.  The regional registries delegate blocks of class C net-
work numbers to  local Internet Registries.  In this way a hierarchy
in the address space is created, which is similar to the hierarchy
in the domain name space. Due to this hierarchy the reverse DNS map-
ping can also be  delegated  in  a  similar model as used for the
normal Domain Name System.

For instance, the RIPE NCC has been delegated the complete  class  C
address space starting with 193. It is therefore possible to
delegate the 193.IN-ADDR.ARPA domain completely to the RIPE NCC,
instead of each and every reverse mapping in the 193.IN-ADDR.ARPA
domain to be registered with the InterNIC. This implies  that all
193.IN-ADDR.ARPA delegations in turn will be done by the RIPE NCC.

Even better, since local registries usually receive blocks of 256
class C networks from the RIPE NCC, the NCC can delegate the reverse
registrations for such complete  blocks  to these  local  regis-
tries. This  implies that customers of these service providers no
longer have to register their reverse domain mapping  with  the
InterNIC or the NCC, but the service providers have authority over
that part of the reverse mapping. This decreases the  workload  on
the InterNIC and the RIPE NCC, and at the same time improves the
service a provider can offer its customers by  improving response
times for reverse mapping changes.

In order to provide a reliable service some procedures have been
agreed and must be followed in order to  avoid confusion  and
inconsistencies.  These procedures are covered in the next section.



Procedures


 1.  A secondary nameserver at ns.ripe.net is mandatory  for
     immediate subdomains of the 193.IN-ADDR.ARPA domain.





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 2.  Because of the importance of correct reverse address mapping,
     for all delegated blocks a good set of secondaries must be
     defined. There should be at least 2 nameservers for all blocks
     delegated, excluding the RIPE NCC secondary.  Operators of the
     primary nameservers should be familiar with RFC1537.



 3.  The delegation of an immediate subdomain of 193.IN-ADDR.ARPA
     domain  corresponding to a block of 256 class C network numbers
     can  be  requested  by sending  a request confirming that the
     procedures described in this document will be followed to
     hostmaster@localhost.  The request should be accompanied by a
     domain object for the RIPE database with all necessary contact
     and  nameserver  information. An example domain object can be
     found at the end of this document.


 4.  When receiveing such a request the RIPE NCC will forward data
     about any currently registered reverse zones inside this  block
     to  the  registry.  After  addition  of these by the registry,
     the NCC will check the working of the reverse server.


 5.  Once everything is set up  properly, the NCC will set up
     ns.ripe.net as secondary nameserver, delegate the block, and
     include the domain object in the RIPE database.


 6.  All reverse servers for blocks  must  be  reachable  from  the
     the Internet.  In short, all servers must meet similar connec-
     tivity requirements as top-level domain servers.


 7.  As with all domain name space, running the reverse server for
     class C blocks does  not  imply that  one  controls  that part
     of the reverse domain.  It only implies that one administers
     that part of the reverse domain. If after repeated complaints
     the delegated name space is still not administered properly the
     RIPE NCC has to revoke the delegation.


 8.  Before adding individual nets, the administrator of a  reverse
     domain  must check whether all servers to be added for these
     nets are indeed set up properly.


 9.  There are some serious implications when a customer that uses
     address space out of the service provider class C blocks, moves
     to another service provider. The  previous service  provider
     cannot force its ex-customer to change network addresses, and
     will have to continue to provide  the appropriate delegation
     records  for reverse mapping of these addresses, even though
     they are no longer belonging to a customer.



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 10. The registration of the reverse zones for individual  class C
     networks  will  usually be done by the registry administering
     the class C block this network has been assigned from.  The
     registry will make the necessary changes to the zone files.
     The registry will also make sure that the network objects in
     the RIPE database for these networks are updated with the
     correct "rev-srv" attributes.


 11. In case the RIPE NCC receives a request for the reverse zone of
     an individual class C network out of a block that has been
     delegated, the request will be forwarded to the mail address
     specified in the SOA RR for the zone concerned.


 12. The NCC advises the following timers and counters  for  direct
     subdomains  of 193.IN-ADDR.ARPA: 8 hours refresh (28800
     seconds), 2 hours retry (7200 seconds), 7 days expire (604800
     seconds)  and 1  day  Time To Live (86400 seconds). The retry
     counter should be lowered where connectivity is unstable.


Above procedures are defined to ensure the necessary high availabil-
ity for  the  reverse domains, and to minimise confusion.  The NCC
will ensure fast response times  for  addition  requests, and will
in principle update the 193.IN-ADDR.ARPA domain at least once per
working day, if needed.



Example domain object to request a block delegation


        domain:  202.193.in-addr.arpa
        descr:   Pan European Organisations class C block
        admin-c: Daniel Karrenberg
        tech-c:  Marten Terpstra
        zone-c:  Marten Terpstra
        nserver: ns.eu.net
        nserver: sunic.sunet.se
        nserver: ns.ripe.net
        changed: marten@localhost 930319
        source:  RIPE



Delegation of Individual Network Zones



The registration of the reverse zones for individual class C net-
works will  usually  be  done  by the registry administering the
class C block this network has been assigned from.




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If the subdomain has not yet been delegated to the registry con-
cerned the RIPE NCC will register the individual networks. However
this service is only provided at a "best-effort" level and no ser-
vice guarantees are given.  The local registries should whenever
possible provide this service locally.

The NCC uses the following procedures for the delegation of indivi-
dual network zones. Local registries should use similar guidelines.


 1.  Because of the importance of  correct  reverse  address  map-
     ping, for  all delegated networks a good set of secondaries
     must be defined. There should be at least two nameservers for
     all networks delegated.


 2.  Each "rev-srv" attribute in the RIPE database should ONLY con-
     tain  one  fully  qualified domain  name  of a nameserver which
     is authoritative for the reverse zone for this network. There
     should be one "rev-srv" attribute for each nameserver.


 3.  If a network has or is going to have any external  connec-
     tivity, it is strongly recommended that it has at least one
     reverse nameserver that can be reached from all of the Inter-
     net.


 4.  Although we do our best to check the setup of the nameservers,
     these  do not receive  the  same level of scrutiny as
     nameservers for blocks of class C network numbers. It is the
     responsibility of the network contacts to ensure proper opera-
     tion.


 5.  Any problems regarding the reverse zones  in  193.IN-ADDR.ARPA
     should be reported to hostmaster@localhost.



The NCC also suggests that similar procedures are set up for  the
delegation  of reverse zones for individual class C networks from
the registries to individual organisations.



If you have any questions or suggestions concerning this document,
please contact the RIPE NCC at hostmaster@localhost.









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