RFC 2036 (rfc2036) - Page 2 of 9
Observations on the use of Components of the Class A Address Space within the Internet
Alternative Format: Original Text Document
RFC 2036 Components of the Class A Address Space October 1996
for, and nature of, such changes as they effect network domains and
network service providers are outlined in this document.
Current Practice with Address Allocations
To date the allocation of class-less network prefixed address blocks
has followed a conservative practice of using address allocations
which are compatible superblocks of Class C addresses, while the
allocation of addresses within the space of Class A and Class B
networks has continued to be aligned with the class-based prefix
structure.
Within this address allocation environment for non-transit network
domains there is accordingly the option to continue to use address
deployment strategies which involve fixed subnet address structures
within contiguous areas, and use Class-full interior routing
protocols. In the situation where variable length subnet masks or
disconnected subnets are deployed within the network domain's routing
structure, interior routing protocols which use subnet-based routing
of Class-full networks can still be successfully deployed and the end
network has the option of using an explicit or implicit sink subnet
default route. Where such non-transit network domains are connected
to the Internet infrastructure the boundary exchange between the
non-transit network and the network service provider (this term is
used as a synonym for a transit network domain, which provides a
traffic transit service to other non-transit and peer transit network
domains) is either a class-full advertisement of routes, or an
aggregated address advertisement where the aggregate is a superblock
of the deployed component class-full networks. At the boundary points
of the non-transit network it is a requirement that the non-transit
network's subnet default route (if used explicitly) not be directed
to the network service provider's domain, to avoid a routing loop at
the domain boundary point.
For network service providers the interior routing protocol can use
either aggregated routing or explicit class-full routing within this
environment. At the network service provider's boundary peering
points the strongly recommended practice is to advertise aggregated
routes to transit peers, which in turn may be further aggregated
across the Internet, within the parameters of permissible policies.
Huston Informational