rfc1195.txt

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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 "[e-mail]".

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



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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




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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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RFC 1195         OSI ISIS for IP and Dual Environments     December 1990


   simultaneously provide an efficient routing protocol for TCP/IP, and
   for OSI. This design makes use of the OSI IS-IS routing protocol,
   augmented with IP-specific information. This design provides explicit
   support for IP subnetting, variable subnet masks, TOS-based routing,
   and external routing. There is provision for authentication
   information, including the use of passwords or other mechanisms. The
   precise form of authentication mechanisms (other than passwords) is
   outside of the scope of this document.

   Both OSI and IP packets are forwarded "as is" -- i.e., they are
   transmitted directly over the underlying link layer services without
   the need for mutual encapsulation. The integrated IS-IS is a dynamic
   routing protocol, based on the SPF (Dijkstra) routing algorithm.

   The protocol described in this specification allows for mixing of
   IP-only, OSI-only, and dual (IP and OSI) routers, as defined below.

   An IP-only IS-IS router (or "IP-only" router) is defined to be a
   router which: (i) Uses IS-IS as the routing protocol for IP, as
   specified in this report; and (ii) Does not otherwise support OSI
   protocols. For example, such routers would not be able to forward OSI
   CLNP packets.

   An OSI-only router is defined to be a router which uses IS-IS as the
   routing protocol for OSI, as specified in [1]. Generally, OSI-only
   routers may be expected to conform to OSI standards, and may be
   implemented independent of this specification.

   A dual IS-IS router (or "dual" router) is defined to be a router
   which uses IS-IS as a single integrated routing protocol for both IP
   and OSI, as specified in this report.

   This approach does not change the way that IP packets are handled.
   IP-only and dual routers are required to conform to the requirements
   of Internet Gateways [4]. The integrated IS-IS protocol described in
   this report outlines an Interior Gateway Protocol (IGP) which will
   provide routing within a TCP/IP routing domain (i.e., autonomous
   system). Other aspects of router functionality (e.g., operation of
   ICMP, ARP, EGP, etc.) are not affected by this proposal.

   Similarly, this approach does not change the way that OSI packets are
   handled. There will be no change at all to the contents nor to the
   handling of ISO 8473 Data packets and Error Reports, nor to ISO 9542
   Redirects and ES Hellos. ISO 9542 IS Hellos transmitted on LANs are
   similarly unchanged. ISO 9542 IS Hellos transmitted on point-to-point
   links are unchanged except for the addition of IP-related
   information.  Similarly, other OSI packets (specifically those
   involved in the IS-IS intra-domain routing protocol) remain unchanged



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RFC 1195         OSI ISIS for IP and Dual Environments     December 1990


   except for the addition of IP-related information.

   This approach makes use of the existing IS-IS packets, with IP-
   specific fields added. Specifically: (i) authentication information
   may be added to all IS-IS packets; (ii) the protocols supported by
   each router, as well as each router's IP addresses, are specified in
   ISO 9542 IS Hello, IS-IS Hello and Link State Packets; (iii)
   internally reachable IP addresses are specified in all Link State
   Packets; and (iv) externally reachable IP addresses, and external
   routing protocol information, may be specified in level 2 Link State
   Packets. The detailed encoding and interpretation of this in
   formation is specified in sections 3, 4, and 5 of this RFC.

   The protocol described in this report may be used to provide routing
   in an IP-only routing domain, in which all routers are IP-only.
   Similarly, this protocol may be used to provide routing in a pure
   dual domain, in which all routers are dual. Finally, this protocol
   may be used to provide routing in a mixed domain, in which some
   routers are IP-only, some routers are OSI-only, and some routers are
   dual. The specific topological restrictions which apply in this
   latter case are described in detail in section 1.4 ("Support of Mixed
   Routing Domains").  The use of IS-IS for support of pure OSI domains
   is specified in [1].

   This protocol specification does not constrain which network
   management protocol(s) may be used to manage IS-IS-based routers.
   Management information bases (MIBs) for managing IP-only, OSI-only,
   and dual routers, compatible with CMIP, CMOT, and/or SNMP, are the
   subject of a separate, companion document [8].

1.2 Overview of the ISO IS-IS Protocol

   The IS-IS Routing Protocol has been developed in ISO to provide
   routing for pure OSI environments. In particular, IS-IS is designed
   to work in conjunction with ISO 8473 (The ISO Connectionless Network
   Layer Protocol [2]), and ISO 9542 (The ISO End System to Intermediate
   System Protocol [3]). This section briefly describes the manner in
   which IS-IS is used to support pure OSI environments. Enhancements
   for support of IP and dual environments are specified elsewhere in
   this report.

   In IS-IS, the network is partitioned into "routing domains". The
   boundaries of routing domains are defined by network management, by
   setting some links to be "exterior links". If a link is marked as
   "exterior", no IS-IS routing messages are sent on that link.

   Currently, ISO does not have a standard for inter-domain routing
   (i.e., for routing between separate autonomous routing domains).