RFC 1520 (rfc1520) - Page 2 of 9

Exchanging Routing Information Across Provider Boundaries in the CIDR Environment

RFC 1520           CIDR Provider Information Exchange     September 1993


   This document defines a CIDR-capable provider as the provider that
   can perform correct IP packet forwarding (both internally and to
   other adjacent providers) when the inter-domain routing information
   acquired by the provider is expressed solely in terms of IP address
   prefixes (with no distinction between A/B/C class of addresses).

   This document defines CIDR-capable forwarding as the ability of a
   router to maintain its forwarding table and to perform correct
   forwarding of IP packets without making any assumptions about the
   class of IP addresses.

   This document defines CIDR reachability information as reachability
   information that may violate any assumptions about the class of IP
   addresses. For instance, a contiguous block of class C networks
   expressed as a single IP address prefix constitutes CIDR reachability
   information.

2.  Taxonomy of Service Providers

   For the purpose of this document we partition all service providers
   into the following categories, based on the type and volume of
   inter-domain routing information a provider needs to acquire in order
   to meet its service requirements:

      - Requirements imposed on a service provider preclude it from
        using Default inter-domain route(s) -- we'll refer to such a
        pqrovider as a Type 1 provider.

      - Requirements imposed on a service provider allow it to rely on
        using one or more Default routes for inter-domain routing, but
        this information must be supplemented by requiring the provider
        to acquire a large percentage of total Internet routing
        information -- we'll refer to such a provider as a Type 2
        provider.

      - Requirements imposed on a service provider allow it to rely on
        using one or more Default routes for inter-domain routing;
        however, to meet its service requirements the provider must
        supplement Default route(s) by acquiring a small percentage of
        total Internet routing information -- we'll refer to such a
        provider as a Type 3 provider.

      - Requirements imposed on a service provider allow it to rely
        solely on using one or more Default routes for inter-domain
        routing; no other inter-domain routing information need to be
        acquired -- we'll refer to such a provider as a Type 4 provider.





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