RFC 2036 (rfc2036) - Page 3 of 9

Observations on the use of Components of the Class A Address Space within the Internet

RFC 2036        Components of the Class A Address Space     October 1996


Implications of Address Allocation from the Class A space

Network Service Providers Must Use Class-less Routing

   For network service providers within the deployed Internet the
   implications from this recommendation to deploy prefixes from the
   Class A address space add more pressure to the requirement to
   uniformly deploy class-less routing protocols. While this is already
   a mandatory requirement for any domain which operates without a
   default  route (ie. the provider carries full Internet routing and
   effectively  calculates default), other providers currently can use
   an imported default route and operate within a class-full routing
   configuration. This mode of operation is sub-optimal, in so far as
   the task of aggregating routes falls on peer network service
   providers performing proxy aggregation of contiguous class-full
   address blocks.

   In deploying components of the Class A the use of proxy aggregation
   is no longer sufficient. Where a domain sees a default route and a
   subnet of a Class A route the routing structure, in a class-full
   configuration, may not necessarily follow the default route to reach
   other parts of the Class A network not covered by the advertised
   Class A subnet route.

   Accordingly for Network Service Providers operating within the
   Internet domain the deployment of components of the Class A space
   entails a requirement to deploy class-less routing protocols, even in
   the presence of a default route. It is noted that this absolute
   requirement is not the case at present.

Consideration of Non-Transit Network Configurations

   For disconnected network environments, where the network domain is
   operated with no links to any peer networking domain, such networks
   can continue to use class-full interior routing protocols with subnet
   support. Allocation of addresses using prefix blocks from the Class A
   space within such environments is possible without adding any
   additional routing or address deployment restrictions on the network
   domain.












Huston                       Informational