RFC1668

Network Working Group D. Estrin Request for Comments: 1668 USC Category: Informational T. Li

                                                       Cisco Systems
                                                          Y. Rekhter
                              T.J. Watson Research Center, IBM Corp.
                                                         August 1994

             Unified Routing Requirements for IPng

Status of this Memo

This memo provides information for the Internet community. This memo does not specify an Internet standard of any kind. Distribution of this memo is unlimited.

Abstract

This document was submitted to the IETF IPng area in response to RFC 1550. Publication of this document does not imply acceptance by the IPng area of any ideas expressed within. Comments should be submitted to the [email protected] mailing list.

IPng Requirements

The following list provides requirements on the IPng from the perspective of the Unified Routing Architecture, as describe in RFC 1322.

1. To provide scalable routing, IPng addressing must provide support

  for topologically significant address assignment.

2. Since it is hard to predict how routing information will be

  aggregated, the IPng addressing structure should impose as few
  preconditions as possible on the number of levels in the hierarchy.
  Specifically, the number of levels must be allowed to be different
  at different parts in the hierarchy. Further, the levels must not
  be statically tied to particular parts (fields) in the addressing
  information.

3. Hop-by-hop forwarding algorithm requires IPng to carry enough

  information in the Network Layer header to unambiguously determine
  a particular next hop. Unless mechanisms to compute
  context-sensitive forwarding tables and provide consistent
  forwarding are defined, the requirement assumes the presence of
  full hierarchical addresses.  Therefore, IPng packet format must
  provide efficient determination of the full hierarchical

  destination address.

4. Hierarchical address assignment should not imply strictly

  hierarchical routing. Therefore, IPng should carry enough
  information to provide forwarding along both hierarchical and
  non-hierarchical routes.

5. The IPng packet header should accommodate a "routing label" or

  "route ID". This label will be used to identify a particular FIB
  to be used for packet forwarding by each router.

  Two types of routing labels should be supported: "strong" and
  "weak".

  When a packet carries a "strong" routing label and a router does
  not have a FIB with this label, the packet is discarded (and an
  error message is sent back to the source).

  When a packet carries a "weak" routing label and a router does not
  have a FIB with this label, the packet should be forwarded via a
  "default" FIB, i.e., according to the destination address. In
  addition, the packet should carry an indication that somewhere
  along the path the desired routing label was unavailable.

6. IPng should provide a source routing mechanism with the following

  capabilities (i.e., flexibility):

   - Specification of either individual routers or collections of
     routers as the entities in the source route.

   - The option to indicate that two consecutive entities in a
     source route must share a common subnet in order for the
     source route to be valid.

   - Specification of the default behavior when the route to
     the next entry in the source route is unavailable:

   - The packet is discarded, or

   - The source route is ignored and the packet is forwarded based
     only on the destination address (and the packet header will
     indicate this action).

   - A mechanism to verify the feasibility of a source route.

Security Considerations

Security issues are not discussed in this memo.

Authors' Addresses

Deborah Estrin University of Southern California Computer Science Department, MC 0782 Los Angeles, California 90089-0782

Phone: (310) 740-4524 EMail: [email protected]

Tony Li cisco Systems, Inc. 1525 O'Brien Drive Menlo Park, CA 94025

EMail: [email protected]

Yakov Rekhter T.J. Watson Research Center IBM Corporation P.O. Box 218 Yorktown Heights, NY 10598

Phone: (914) 945-3896 EMail: [email protected]