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This documents obsoletes ripe-65, version 0.6 of this document


This document describes the policy for reverse delegation of IPv4 and IPv6 address space in the RIPE NCC service region.


1.0 Introduction Link: #intro
2.0 Obtaining Delegation of an or sub-domain Link: #delegation
3.0 Procedures Link: #procedures
4.0 References Link: #references

1.0 Introduction

The RIPE NCC provides, as part of its services, the necessary support to enable the reverse resolution of IPv4 and IPv6 address space into domain names. This service is implemented under the and sub-domains described in [1 Link: #references ] and [2 Link: #references ].

Reverse delegations for IPv4 and IPv6 addresses allocated by the RIPE NCC are made to Local Internet Registries (LIRs) and further delegated by the LIRs to Internet Service Providers or End Users.

2.0 Obtaining Delegation of an or sub-domain

The RIPE NCC provides reverse delegation for address space that has been allocated or assigned by the RIPE NCC. It also provides systems to control reverse delegations relating to early registrations that have been transferred to the RIPE Database. Registrants of address space allocations or assignments may delegate authority for requesting reverse delegation from the RIPE NCC.

The RIPE NCC accepts requests for reverse delegation for address space that has been allocated by the RIPE NCC to an LIR or, in the case of PI address space, an assignment that has been made to an End User.

3.0 Procedures

The procedures for requesting and modifying reverse delegation and information about the requirements the RIPE NCC enforces to maintain the quality of the reverse delegations are published at: Link: /manage-ips-and-asns/dns/reverse-dns/

4.0 References

[1] "Management Guidelines & Operational Requirements for the Address and Routing Parameter Area Domain ("arpa")"
[RFC 3172 Link: ]

[2] "DNS Extensions to Support IPv6 Address Aggregation and Renumbering" [RFC 2874 Link: ]

procedures for the reassignment of IP
network numbers from blocks obtained from the RIPE Network Coordination
Centre. It deals with items as providing information for the RIPE
database, as well as reassignment of IP addresses in light of
the "Supernetting" proposal, as documented in RFC 1338, by Vince Fuller
et al.


Since May 1st 1992, the RIPE Network Coordination Centre (NCC) is
acting as a delegated registry for IP networks numbers to NICs and NOCs
in Europe. It is RIPE NCC policy not to give out network numbers to
individual organisations, who should refer in turn, to their IP network
service provider.

The mission of the RIPE NCC is to give network numbers to the various
service providers and NICs. The NICs and NOCs can then reassign the
actual IP network numbers to organisations requesting IP network

Class B Network Number Allocation Procedure

Service providers can request Class B network numbers on a one-by-one
basis from the RIPE NCC. Because class B address space is a critical
resource, a request for a class B network number must be accompanied by
a justification in terms of the requesting organisation's size, current
network and expected network growth. The requestor should also make
clear why they cannot use a block of class C network numbers to achieve
their goals. The RIPE NCC will review requests using the same standards
as any other Internet Registry, particularly the US NIC.

Class C Allocation Procedures

NICs and NOCs accepting a block of class C numbers agree to adhere to
the following procedures:

A) The RIPE NCC will assign complete class C blocks to individual NICs
and NOCs. They can be requested from <[email protected]>.

B) In order to prevent implementation problems, network numbers ending
with 0 or 255 should NOT be reassigned.

C) Full information about reassigned network numbers must be reported
back to the RIPE NCC in full RIPE database format (ref ripe-13).
The complete entries should be sent immediately after reassignment to
<[email protected]>.
The RIPE NCC is ready to accept block entries for the RIPE database.
For block syntax, please contact the RIPE NCC.

D) Reassignment of class C network numbers should be done in a manner
that facilitates Supernetting (see next section).

E) Requests for network numbers should be reasonable. All NICs and NOCs
should prevent stockpiling of network numbers.

F) On first request from the RIPE NCC, the class C network numbers not
yet reassigned, must be returned to the RIPE NCC.


NICs and NOCs reassigning IP network numbers are urgently requested to
read the Supernetting proposal by Vince Fuller et al. This document can
be obtained from the rfc section of the RIPE document store or other RFC
servers. It is called rfc1338.txt.
The Supernetting proposal was made to reduce the increase of routing
table size in the current Internet. It proposes to create a hierarchy
of IP network numbers, which can then be aggregated resulting in less
routing table entries in routing equipment. While this proposal has not
been formally adopted we expect that something at least along the same
principle will be implemented in the near future.

Here is how it works:

If an organisation A needs 8 class C network numbers, the numbers should
be given out in such a way that the routing information for each of
these 8 networks could appear as one entry with the correct mask in

More concretely:

Service provider S hands out networks 192.24.8 through 192.24.15 to
organisation A. These networks can then appear in routing equipment as a
supernet route to 192.24.8 with mask This way 8 class C
network numbers appear as one routing table entry.

The guidelines that can be derived from the Supernetting proposal are:

A) Service providers should reserve blocks of class C network numbers from
their allocation for each organisations requesting class C network numbers.

B) The size of these blocks should always be a power of 2.

C) The numbers in these blocks should be contiguous.

D) The blocks should start on bit boundaries.
(ie powers of 2, AND multiples of the block size)

E) The blocks reserved for an organisation should be sufficient for a
reasonable expected growth over the next few years.

F) Multi-homed organizations may obtain address space from one of their
providers, the RIPE NCC, or the global NIC, as is appropriate to their
network configuration. These organisations are strongly encouraged to
contact the RIPE NCC for guidance.

If you have any questions concerning this, please do not hesitate to
call or mail us at [email protected].