Guidelines For The Delegation Of Zones In The 193.in-addr.arpa Domain
This document describes the procedures for the delegation of au-
thority of zones in the 193.in-addr.arpa domain. As of March
16th 1993 the RIPE NCC has been delegated the authority for the
193.in-addr.arpa domain from the root. Due to the fact that in
the 193.x.y address space blocks of 256 class C network numbers
are further delegated to local registries , the possibility ex-
ists to also delegate the zone for these blocks in the 193.in-
addr.arpa domain. This document describes some guidelines and
procedures for this type of delegation and the delegation of re-
verse zones for individual class C networks in 193.x.y.
A bit more explained
With the assignment of class C network numbers following the CIDR
(RFC 1338) model, in which large chunks of the address space are
delegated to one region, and within that region blocks of class C
network numbers are delegated to service providers and non-
provider registries, some hierarchy in the address space is
created, similar to the hierarchy in the domain name space. Due
to this hierarchy the reverse Domain Name System mapping can also
be delegated in a similar model as used for the normal Domain
Name System. For instance, the RIPE NCC has been assigned the
complete class C address space starting with 193. It is there-
fore 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 resistrations will be done by
the RIPE NCC. Even better, since service providers receive com-
plete class C network blocks from the RIPE NCC, the RIPE NCC can
delegate the reverse registrations for such complete blocks to
these local registries. This implies that customers of these
service providers no longer have to register their reverse domain
mapping with the root, but the service provider have authority
over that part of the reverse mapping. This decreases the work-
load on the INTERNIC and the RIPE NCC, and at the same time in-
crease the service a provider can offer its customers by improve
response times for reverse mapping changes . However there are
some things that need to be examined a bit more closely to avoid
confusion and inconsistencies. These issues are covered in the
Procedures for the delegation of direct subdomains of 193.in-
1. A secondary nameserver at ns.ripe.net is mandatory for all
blocks of class C network numbers delegated in the 193.in-
2. Because of the increasing importance of correct reverse ad-
dress 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.
3. The delegation of a class C block in the 193.in-addr.arpa
domain can be requested by sending in a domain object for the
RIPE database to <email@example.com> with all necessary contact
and nameserver information. The RIPE NCC will then forward all
current reverse zones inside this block to the registry, and
after addition of these by the registry, the NCC will check the
working of the reverse server. Once everything is setup proper-
ly, the NCC will delegate the block, and submit the database ob-
ject for inclusion in the database. An example domain object can
be found at the end of this document.
4. All reverse servers for blocks must be reachable from the
whole of the Internet. In short, all servers must meet similar
connectivity requirements as top-level domain servers.
5. Running the reverse server for class C blocks does not imply
that one controls that part of the reverse domain, it only im-
plies that one administers that part of the reverse domain.
6. Before adding individual nets, the administrator of a reverse
domain must check wether all servers to be added for these nets
are indeed setup properly.
7. There are some serious implications when a customer of a ser-
vice provider 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 it they are no longer belonging to a customer.
8. 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, and update the net-
work objects in the RIPE database for these networks, to reflect
the correct "rev-srv" fields. 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 zone contact for this reverse block.
9. 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 availa-
bility for the 193 reverse domains, and to minimize confusion.
The NCC will ensure fast repsonse times for addition requests,
and will in principle update the 193.in-addr.arpa domain at least
once per working day.
Example domain object to request a block delegation
descr: Pan European Organisations class C block
admin-c: Daniel Karrenberg
tech-c: Marten Terpstra
zone-c: Marten Terpstra
changed: firstname.lastname@example.org 930319
Procedures for the delegation of individual network zones by the
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. In case the
zone corresponding to the class C block has not been delegated,
the RIPE NCC will automatically add the reverse nameserver as
specified in the "rev-srv" attribute of the RIPE database object
for this network, using the following procedures:
1. Because of the increasing importance of correct reverse ad-
dress mapping, for all delegated networks a good set of secon-
daries must be defined. There should be at least two nameservers
for all networks delegated.
2. The "rev-srv" field should ONLY contain one fully qualified
domain name of a nameserver which is authoritative for the re-
verse zone for this network.
3. If a network has or is going to have any external connectivi-
ty, it is strongly recommended that it has at least one reverse
nameserver that can be reached from all of the Internet.
4. The checking and addition of the reverse zones for single net-
works is completely automated at the RIPE NCC. Although we do
our best to check the setup of the nameservers, these does 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 operation.
5. Any problems regarding the reverse zones in 193.in-addr.arpa
should be directed to <email@example.com>.
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.