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Network Working Working Group                                  R. Callon
Request for Comments: 1195                 Digital Equipment Corporation
                                                           December 1990


      Use of OSI IS-IS for Routing in TCP/IP and Dual Environments

Status of this Memo

   This RFC specifies a protocol on the IAB Standards Track for the
   Internet community, and requests discussion and suggestions for
   improvements. Please refer to the current edition of the "IAB
   Official Protocol Standards" for the standardization state and status
   of this protocol. Distribution of this memo is unlimited.

   This RFC is available in both postscript and text versions. Where
   possible, use of the postscript version is recommended. For example,
   this text version may have figures which are less informative or
   missing.

Abstract

   This RFC specifies an integrated routing protocol, based on the OSI
   Intra-Domain IS-IS Routing Protocol, which may be used as an interior
   gateway protocol (IGP) to support TCP/IP as well as OSI. This allows
   a single routing protocol to be used to support pure IP environments,
   pure OSI environments, and dual environments. This specification was
   developed by the IS-IS working group of the Internet Engineering Task
   Force.

   The OSI IS-IS protocol has reached a mature state, and is ready for
   implementation and operational use. The most recent version of the
   OSI IS-IS protocol is contained in ISO DP 10589 [1]. The proposed
   standard for using IS-IS for support of TCP/IP will therefore make
   use of this version (with a minor bug correction, as discussed in
   Annex B).  We expect that future versions of this proposed standard
   will upgrade to the final International Standard version of IS-IS
   when available.

   Comments should be sent to "isis@merit.edu".

Contents

    1   Introduction: Overview of the Protocol
        1.1     What the Integrated IS-IS offers
        1.2     Overview of the ISO IS-IS Protocol
        1.3     Overview of the Integrated IS-IS
        1.4     Support of Mixed Routing Domains



Callon                                                          [Page 1]

RFC 1195         OSI ISIS for IP and Dual Environments     December 1990


        1.5     Advantages of Using Integrated IS-IS

    2   Symbols and Abbreviations

    3   Subnetwork Independent Functions
        3.1     Exchange of Routing Information
        3.2     Hierarchical Abbreviation of IP Reachability Information
        3.3     Addressing Routers in IS-IS Packets
        3.4     External Links
        3.5     Type of Service Routing
        3.6     Multiple LSPs and SNPs
        3.7     IP-Only Operation
        3.8     Encapsulation
        3.9     Authentication
        3.10    Order of Preference of Routes / Dijkstra Computation

    4   Subnetwork Dependent Functions
        4.1     Link Demultiplexing
        4.2     Multiple IP Addresses per Interface
        4.3     LANs, Designated Routers, and Pseudonodes
        4.4     Maintaining Router Adjacencies
        4.5     Forwarding to Incompatible Routers

    5   Structure and Encoding of PDUs
        5.1     Overview of IS-IS PDUs
        5.2     Overview of IP-Specific Information for IS-IS
        5.3     Encoding of IP-Specific Fields in IS-IS PDUs

    6   Security Considerations

    7   Author's Address

    8   References

    A   Inter-Domain Routing Protocol Information
        A.1     Inter-Domain Information Type
        A.2     Encoding

    B   Encoding of Sequence Number Packets
        B.1     Level 1 Complete Sequence Numbers PDU
        B.2     Level 2 Complete Sequence Numbers PDU
        B.3     Level 1 Partial Sequence Numbers PDU
        B.4     Level 2 Partial Sequence Numbers PDU

    C   Dijkstra Calculation and Forwarding
        C.1     SPF Algorithm for IP and Dual Use
        C.2     Forwarding of IP packets




Callon                                                          [Page 2]

RFC 1195         OSI ISIS for IP and Dual Environments     December 1990


    D   Use of the Authentication Field
        D.1     Authentication Field in IS-IS packets
        D.2     Authentication Type 1 - Simple Password

    E   Interaction of the Integrated IS-IS with Brouters
        E.1     The Problem
        E.2     Possible Solutions

Figures
        1       ISO Hierarchical Address Structure
        2       An Example
        3       Encoding of Variable Length Fields

1 Introduction: Overview of the Protocol

   The TCP/IP protocol suite has been growing in importance as a multi-
   vendor communications architecture. With the anticipated emergence of
   OSI, we expect coexistence of TCP/IP and OSI to continue for an
   extended period of time. There is a critical need for routers to
   support both IP traffic and OSI traffic in parallel.

   There are two main methods that are available for routing protocols
   to support dual OSI and IP routers. One method, known as "Ships in
   the Night", makes use of completely independent routing protocols for
   each of the two protocol suites. This specification presents an
   alternate approach, which makes use of a single integrated protocol
   for interior routing (i.e., for calculating routes within a routing
   domain) for both protocol suites.

   This integrated protocol design is based on the OSI Intra-domain IS-
   IS routing protocol [1], with IP-specific functions added. This RFC
   is considered a companion to the OSI IS-IS Routing spec, and will
   only describe the required additional features.

   By supporting both IP and OSI traffic, this integrated protocol
   design supports traffic to IP hosts, OSI end systems, and dual end
   systems.  This approach is "integrated" in the sense that the IS-IS
   protocol can be used to support pure-IP environments, pure-OSI
   environments, and dual environments. In addition, this approach
   allows interconnection of dual (IP and OSI) routing domains with
   other dual domains, with IP-only domains, and with OSI-only domains.

   The protocol specified here is based on the work of the IETF IS-IS
   working group.

1.1 What the Integrated IS-IS offers

   The integrated IS-IS provides a single routing protocol which will
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