Internet Architecture Extensions for Shared Media
RFC 1620

Document Type RFC - Informational (May 1994; No errata)
Was draft-braden-shared-media (individual)
Last updated 2013-03-02
Stream Legacy
Formats plain text pdf html bibtex
Stream Legacy state (None)
Consensus Boilerplate Unknown
RFC Editor Note (None)
IESG IESG state RFC 1620 (Informational)
Telechat date
Responsible AD (None)
Send notices to (None)
Network Working Group                                          B. Braden
Request for Comments: 1620                                           ISI
Category: Informational                                        J. Postel
                                                                     ISI
                                                              Y. Rekhter
                                                            IBM Research
                                                                May 1994

           Internet Architecture Extensions for Shared Media

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

   The original Internet architecture assumed that each network is
   labeled with a single IP network number.  This assumption may be
   violated for shared media, including "large public data networks"
   (LPDNs).  The architecture still works if this assumption is
   violated, but it does not have a means to prevent multiple host-
   router and router-router hops through the shared medium.  This memo
   discusses alternative approaches to extending the Internet
   architecture to eliminate some or all unnecessary hops.

Table of Contents

   1. INTRODUCTION ..................................................  2
   2. THE ORIGINAL INTERNET ARCHITECTURE ............................  2
   3. THE PROBLEMS INTRODUCED BY SHARED MEDIA .......................  4
   4. SOME SOLUTIONS TO THE SM PROBLEMS .............................  7
      4.1  Hop-by-Hop Redirection ...................................  7
      4.2  Extended Routing ......................................... 11
      4.3  Extended Proxy ARP ....................................... 13
      4.4  Routing Query Messages ................................... 14
      4.5  Stale Routing Information ................................ 14
      4.6  Implications of Filtering (Firewalls) .................... 15
   5. SECURITY CONSIDERATIONS ....................................... 16
   6. CONCLUSIONS ................................................... 17
   7. ACKNOWLEDGMENTS ............................................... 17
   8. REFERENCES .................................................... 18
   Authors' Addresses ............................................... 19

Braden, Postel & Rekhter                                        [Page 1]
RFC 1620              Shared Media IP Architecture              May 1994

1. INTRODUCTION

   This memo concerns the implications of shared medium networks for the
   architecture of the TCP/IP protocol suite.  General familiarity with
   the TCP/IP architecture and the IP protocol is assumed.

   The Internet architecture is founded upon what was originally called
   the "Catenet model" [PSC81].  Under this model, the Internet
   (originally dubbed "the Catenet") is formed using routers (originally
   called "gateways") to interconnect distinct and perhaps diverse
   networks.  An IP host address (more correctly characterized as a
   network interface address) is formed of the pair (net#,host#).  Here
   "net#" is a unique IP number assigned to the network (or subnet) to
   which the host is attached, and "host#" identifies the host on that
   network (or subnet).

   The original Internet model made the implicit assumptions that each
   network has a single IP network number and that networks with
   different numbers may interchange packets only through routers.
   These assumptions may be violated for networks implemented using a
   common "shared medium" (SM) at the link layer (LL).  For example,
   network managers sometimes configure multiple IP network numbers
   (usually subnet numbers) on a single broadcast-type LAN such as an
   Ethernet.  The large (switched) public data networks (LPDNs), such as
   SMDS and B-ISDN, form a potentially more important example of shared
   medium networks.  Any two systems connected to the same shared medium
   network are capable of communicating directly at the LL, without IP
   layer switching by routers.  This presents an opportunity to optimize
   performance and perhaps lower cost by eliminating unnecessary LL hops
   through the medium.

   This memo discusses how unnecessary hops can be eliminated in a
   shared medium, while retaining the coherence of the existing Internet
   architecture.  This issue has arisen in a number of IETF Working
   Groups concerned with LPDNs, including IPLPDN, IP over ATM, IDRP for
   IP, and BGP.  It is time to take a careful look at the architectural
   issues to be solved.  This memo first summarizes the relevant aspects
   of the original Internet architecture (Section 2), and then it
   explains the extra-hop problems created by shared media networks
   (Section 3).  Finally, it discusses some possible solutions (Section
   4).

2. THE ORIGINAL INTERNET ARCHITECTURE
Show full document text