Support for Classless Internet Addresses in the
RIPE Database
Tony Bates
Daniel Karrenberg
Marten Terpstra
Document ID: ripe-121
ABSTRACT
This paper describes the necessary changes to the
RIPE database schema and software in order to support
classless internet addresses.
1. Introduction
The features described in this document will be usable in the RIPE
database at a time specified in [9]. Please refer to this document
for more details.
Classless Inter-Domain Routing (also known as supernetting) defines
a method of address allocation in the Internet, and a mechanism to
reduce routing table size in Internet routers.
The internet (IPv4) address is a 32-bit value split into two parts
called network part and host part to provide hierarchical rout-
ing[1]. The host part of an address is used for local routing, the
network part for global routing. The boundary between the network
and host parts was originally defined by run-length encoding in
three classes called A (8/24 bit network/host), B (16/16) and C
(24/8). This type of internet address will herein after be referred
to as classful address.
The proliferation of local area networks made it necessary to intro-
duce more structure into local routing. This was achieved by "sub-
netting"[2], a technique which divides the host-part of an address
into subnet and host parts. This division is visible only to the
routers connected to the collection of networks designated by the
network part of the address. These routers can use the subnet part
for local routing between subnets. Addresses with subnets are still
classful as the division between the network part and the local
part(s) is still determined by static run-length encoding.
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Classless addresses differ from the classful addresses in that the
division between the network part and the host part is no longer
determined by run-length encoding but by additional information car-
ried in the routing protocols. The additional information is often
represented as and referred to as the address mask. This is a 32-
bit value where 1-bits represent the address bits in the network
part of the address. Classless addressing allows address space to
be allocated in almost totally arbitrary and thus more suitable
sized pieces.
Furthermore the division need not be the same everywhere in the
Internet routing system. As one moves away from the local environ-
ment addresses can be aggregated into more global units forming a
routing hierarchy:
LAN segment < building/department < enterprise < service provider
However this can only be achieved if addresses are allocated accord-
ing to that hierarchy, contiguous and on bit boundaries. The aggre-
gate addresses can then be perceived by routers as a single address,
and thus reduce the size of the routing tables. For details of these
see[3,4]. In CIDR terms the classless internet address if often
known as an "IP prefix":
An IP prefix is a 32-bit value and an indication of the
leftmost contiguous significant bits within this address
representing the network part.
The RIPE Database
The RIPE Database[5] stores information about address space allo-
cated by the RIPE NCC[6] and routing policies of European Internet
service providers[7,8]. The RIPE database schema can currently only
represent classful addresses. With the introduction of CIDR, the
representation of internet addresses in the RIPE database should be
extended to deal with classless addresses. This document details the
current representation of internet addresses in the RIPE database,
and proposes extensions in terms of representation for classless
addressing. This document does not deal with the consequences for
the database query mechanisms. It also does not deal with other
aspects of the database schema.
2. Current Address Representation
Internet addresses are traditionally represented as "dotted quads".
These consist of four decimal numbers in the range of 0-255, each
representing 8 bits of the address starting with the first bit of
the network part. This nicely fits with the 8-bit granularity of
classful addresses.
The current database deals only with classful representation (i.e.
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standard Class A, B and C style addresses). The addresses can be
represented in two ways: classful net and classful range.
2.1. Classful Net
The classful net representation is a dotted quad with zeroes in the
parts representing the host part of the network address. These
represent the whole address range corresponding to the network ad-
dress.
representation range of addresses covered
192.1.1.0 192.1.1.0 - 192.1.1.255
2.2. Classful Range
The classful range representation is two dotted quads separated by
"blank dash blank" (" - "). Both dotted quads represent classful
nets, i.e. the host part of the respective net contains all zeroes.
This represents the address range corresponding to the networks
represented by the first and second dotted quads as well as all ad-
dresses in the interval between them.
representation range of addresses covered
192.1.1.0 - 192.1.2.0 192.1.1.0 - 192.1.2.255
3. Classless Address Representations
Unfortunately, there are a number of representations for classless
addresses in use. While this potentially aids the user in under-
standing classless addressing, it makes it more difficult to use a
single representation. The following choices have to be made w.r.t.
the RIPE database:
- Which representations to accept for the different addresses
that appear in the schema.
- Which representation to use when presenting the information in
response to a query.
We will present the common representations in turn followed by a
discussion on how they are used in the RIPE DB for submission and
presentation of classless addresses.
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3.1. Prefix Length
This representation is a dotted quad followed by a slash and the de-
cimal length in bits of the prefix. This is used in the CIDR[4] and
BGP-4[9] documents as well as in popular router software.
representation range of addresses covered
192.1.1.0/24 192.1.1.0 - 192.1.1.255
192.1.128.0/17 192.1.128.0 - 192.1.255.255
If we look at these examples in terms of the mask depicted by the
length we seeing the following:
10 20 30
+----------|----------|----------|--+
|12345678 12345678 12345678 12345678|
|===================================|
24 = |11111111 111111111 1111111 00000000|
17 = |11111111 111111111 1000000 00000000|
+-----------------------------------+
Table 1: mask length as network bits in 32 bit IP address
Table 1 shows which bits form the network part (represented by "1"s)
for the two example lengths of `network prefix' (24 and 17) given.
3.2. Network and Mask
This representation is based on the subnet mask representation. It
is a dotted quad representing the address followed by whitespace and
a dotted quad representing the mask covering the prefix bits.
representation range of addresses covered
192.1.1.0 255.255.255.0 192.1.1.0 - 192.1.1.255
192.1.128.0 255.255.128.0 192.1.128.0 - 192.1.255.255
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3.3. Classless Range
This representation is a dotted quad followed by "blank hyphen
greater-than blank" and another dotted quad. This representation is
specific to the RIPE database. This represents the range defined by
the classless addresses represented by the first and second dotted
quad well as all addresses between them. The difference to the
classful range representation is that the host part of the high end
of the range is not assumed to be all ones.
It should be noted that this representation is the only representa-
tion in which one can specify a range that is not necessarily bit-
aligned. Although this should be avoided in light of CIDR, it does
make this representation the most flexible of the three.
representation range of addresses covered
192.1.1.0 -> 192.1.1.255 192.1.1.0 - 192.1.1.255
192.1.128.0 -> 192.1.255.255 192.1.128.0 - 192.1.255.255
The separator between the begin address and end address has changed
to clearly indicate the different semantics.
representation range of addresses covered hosts
192.1.1.0 - 192.1.2.0 192.1.1.0 - 192.1.2.255 512
192.1.1.0 -> 192.1.2.0 192.1.1.0 - 192.1.2.0 257
4. New representation of IP addresses in the RIPE database
The choice of representation of IP addresses in the RIPE database is
depending on the context. The first part concerns the object in the
database that deals with address assignment information, the inetnum
object, the second concerns the newly proposed object that contains
routing information, the route object [8].
4.1. Representation in the "inetnum" object
With the newly proposed route object, the inetnum object will only
contain assignment information. Because of the large number of
entries currently in the database using the classful net and class-
ful range representation, these two representation will remain
valid. New to the inetnum will be the classless range representa-
tion.
Representations accepted
To help registries when sending in assignment information, the net-
work and mask notation and the prefix/length notation will be
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accepted by the software in addition to the three notations men-
tioned above, but they will be rewritten by the software to the
classless range notation. The database output will only contain the
classful net and range notation and the classless range notation.
The table below shows some rewrite examples.
representation rewritten to
192.87.45.0/24 192.87.45.0 -> 192.87.45.255
192.1.128.0 255.255.128.0 192.1.128.0 -> 192.1.255.255
Please note that non-contiguous subnet masks will not be allowed.
It should also be noted that the classless range representation is
the only representation that supports subnets of the existing class-
ful style networks. While these subnets can be expressed in
prefix/length and network and mask representation, they will always
be rewritten to a classless range.
4.2. Representation in the "route" object
The route object will contain routing information for IP address
space. Because many vendors have implemented the prefix/length nota-
tion, the route object shall only contain this representation.
Representations accepted
All other representations, classful and classless, will be accepted
by the database software, but will be rewritten to the prefix/length
representation if possible.
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In cases where there is no one to one mapping between the represen-
tation sent in and the prefix/length representation, an error will
be generated, and the object will be refused. These cases happen
when ranges cannot be represented by a common mask, i.e. do not
start and end on a common bit boundary.
This means that objects that would require to be split into multiple
prefix/length representations will not be accepted. The table below
shows some rewrite examples.
representation rewritten to
192.87.45.0 192.87.45.0/24
192.1.128.0 - 192.1.255.0 192.1.128.0/17
192.1.128.0 -> 192.1.255.255 192.1.128.0/17
192.1.128.0 255.255.128.0 192.1.128.0/17
192.87.45.0 - 192.87.46.0 ERROR
192.1.128.0 -> 192.1.130.255 ERROR
Please note that also here non-contiguous subnet masks will not be
allowed.
5. References
[1] J. Postel, "Internet Protocol", RFC 791, January 1981.
[2] J. Mogul, "Internet subnets", RFC 917, January 1984.
[3] Fuller, V., Li, T., Yu, J., Varadhan, K., "Supernetting: an Ad-
dress Assignment and Aggregation Strategy", RFC 1519, September
1993.
[4] Y. Rekhter, T. Li, "An Architecture for IP Address Allocation
with CIDR", RFC 1518, September 1993.
[5] R. Blokzijl, "RIPE Databases", ripe-013, August 1990.
[6] D. Karrenberg, M. Terpstra, "IP Address Space Assignment Pro-
cedures", ripe-104, December 1993.
[7] T. Bates, J-M. Jouanigot, D. Karrenberg, P. Lothberg, M.
Terpstra, "Representation of IP Routing Policies in the RIPE
Database", ripe-081, February 1993.
[8] T. Bates, Gerich, E., Joncheray, L., Joanigot, J-M, Karrenberg,
D., Terpstra, M, Yu, J., "Representation of IP Routing Policies
in the RIPE Database", ripe-181, October 1994.
[9] T. Bates,D. Karrenberg, M. Terpstra, "RIPE Database Transition
Plan", ripe-123, October 1994.
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