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 big-internet@munnari.oz.au mailing list.

1. 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: estrin@usc.edu

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

EMail: tli@cisco.com

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

Phone: (914) 945-3896
EMail: yakov@watson.ibm.com