RFC 2036 (rfc2036) - Page 2 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


   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