isis                                                         B. Liu, Ed.
Internet-Draft                                       Huawei Technologies
Intended status: Standards Track                             L. Ginsberg
Expires: November 10, 2017                                 Cisco Systems
                                                             B. Decraene
                                                               I. Farrer
                                                     Deutsche Telekom AG
                                                          M. Abrahamsson
                                                             May 9, 2017

                        ISIS Auto-Configuration


   This document specifies IS-IS auto-configuration mechanisms.  The key
   components are IS-IS System ID self-generation, duplication detection
   and duplication resolution.  These mechanisms provide limited IS-IS
   functions, and so are suitable for networks where plug-and-play
   configuration is expected.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "OPTIONAL" in this document are to be interpreted as described in
   [RFC2119] when they appear in ALL CAPS.  When these words are not in
   ALL CAPS (such as "should" or "Should"), they have their usual
   English meanings, and are not to be interpreted as [RFC2119] key

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

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   This Internet-Draft will expire on November 10, 2017.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   ( in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Protocol Specification  . . . . . . . . . . . . . . . . . . .   3
     3.1.  IS-IS Default Configuration . . . . . . . . . . . . . . .   3
     3.2.  IS-IS NET Generation  . . . . . . . . . . . . . . . . . .   4
     3.3.  Router-Fingerprint TLV  . . . . . . . . . . . . . . . . .   5
     3.4.  Protocol Operation  . . . . . . . . . . . . . . . . . . .   6
       3.4.1.  Start-Up mode . . . . . . . . . . . . . . . . . . . .   6
       3.4.2.  Adjacency Formation . . . . . . . . . . . . . . . . .   7
       3.4.3.  IS-IS System ID Duplication Detection . . . . . . . .   7
       3.4.4.  Duplicate System ID Resolution Procedures . . . . . .   7
       3.4.5.  System ID and Router-Fingerprint Generation
               Considerations  . . . . . . . . . . . . . . . . . . .   8
       3.4.6.  Duplication of both System ID and Router-Fingerprint    9
     3.5.  Additional IS-IS TLVs Usage Guidelines  . . . . . . . . .  10
       3.5.1.  Authentication TLV  . . . . . . . . . . . . . . . . .  11
       3.5.2.  Metric Used in Reachability TLVs  . . . . . . . . . .  11
       3.5.3.  Dynamic Host Name TLV . . . . . . . . . . . . . . . .  11
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  12
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  12
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

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1.  Introduction

   This document specifies mechanisms for IS-IS [RFC1195]
   [ISO_IEC10589][RFC5308] to be auto-configuring.  Such mechanisms
   could reduce the management burden for configuring a network,
   especially where plug-and-play device configuration is required.

   IS-IS auto-configuration is comprised of the following functions:

   1.  IS-IS default configuration.

   2.  IS-IS System ID self-generation.

   3.  System ID duplication detection and resolution.

   4.  ISIS TLV utilization (Authentication TLV, metrics in reachability
       advertisements, and Dynamic Host Name TLV).

   This document also defines mechanisms to prevent the unintentional
   interoperation of auto-configured routers with non-autoconfigured
   routers.  See Section 3.3.

2.  Scope

   The auto-configuration mechanisms support both IPv4 and IPv6

   These auto-configuration mechanisms aim to cover simple deployment
   cases.  The following important features are not supported:

   o  Multiple IS-IS instances.

   o  Multi-area and level-2 routing.

   o  Interworking with other routing protocols.

   IS-IS auto-configuration is primarily intended for use in small (i.e.
   10s of devices) and unmanaged deployments.  It allows IS-IS to be
   used without the need for any configuration by the user.  It is not
   recommended for larger deployments.

3.  Protocol Specification

3.1.  IS-IS Default Configuration

   o  IS-IS interfaces MUST be auto-configured to an interface type
      corresponding to their layer-2 capability.  For example, Ethernet
      interfaces will be auto-configured as broadcast networks and

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      Point-to-Point Protocol (PPP) interfaces will be auto-configured
      as Point-to-Point interfaces.

   o  IS-IS auto-configuration instances MUST be configured as level-1,
      so that the interfaces operate as level-1 only.

   o  originatingLSPBufferSize is set to 512.

   o  MaxAreaAddresses is set to 3

   o  Extended IS Reachability and IP Reachability TLVs [RFC5305] MUST
      be used i.e. a router operating in auto configuration mode MUST
      NOT use any of the following TLVs:

      *  IS Neighbors (2)

      *  IP Internal Reachability (128)

      *  IP External Reachability (130)

      TLVs listed above MUST be ignored on receipt.

3.2.  IS-IS NET Generation

   In IS-IS, a router (known as an Intermediate System) is identified by
   a Network Entity Title (NET) which is a type of Network Service
   Access Point (NSAP).  The NET is the address of an instance of the
   IS-IS protocol running on an Intermediate System (IS).

   The auto-configuration mechanism generates the IS-IS NET as the

   o  Area address

         In IS-IS auto-configuration, this field MUST be 13 octets long
         and set to all 0.

   o  System ID

         This field follows the area address field, and is 6 octets in
         length.  There are two basic requirements for the System ID

         -  As specified by the IS-IS protocol, this field must be
            unique among all routers in the same area.

         -  After its initial generation, the System ID SHOULD remain
            stable.  Changes such as interface enable/disable, interface

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            connect/disconnect, device reboot, firmware update, or
            configuration changes SHOULD NOT cause the system ID to
            change.  System ID change as part of the System ID collision
            resolution process MUST be supported.  Implementations
            SHOULD allow the System ID to be cleared by a user initiated
            system reset.

         More specific considerations for System ID generation are
         described in Section 3.4.5.

3.3.  Router-Fingerprint TLV

   The Router-Fingerprint TLV is similar to the Router-Hardware-
   Fingerprint TLV defined in [RFC7503].  However, the TLV defined here
   includes a flags field to support indicating that the router is in
   Start-up mode and is operating in auto-configuration mode.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   |     Type      |    Length     |
   |  Flags Field  |                                               |
   +-+-+-+-+-+-+-+-+        Router Fingerprint (Variable)          .
   .                                                               .
   .                                                               .

   Type: to be assigned by IANA.
   Length: the length of the value field. Must be >= 33.
   Flags field (1 octet)

    0 1 2 3 4 5 6 7
   |S|A| Reserved  |

   S flag: when set, indicates the router is in "start-up" mode.
   A flag: when set, indicates that the router is operating in
     auto-configuration mode. The purpose of the flag is so that
     two routers can identify if they are both using auto-configuration.
     If the A flag setting does not match in hellos then no adjacency
     should be formed.
   Reserved: these bits MUST be set to zero and MUST be ignored by
     the receiver.

   Router Fingerprint: 32 or more octets.

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   More specific considerations for Router-Fingerprint are described in
   Section 3.4.5.

   Router Fingerprint TLV MUST be included in Intermediate System to
   Intermediate System Hellos (IIHs) originated by a router operating in
   auto-configuration mode.  An auto-configuration mode router MUST
   ignore IIHs that don't contain the Router Fingerprint TLV.

   Router Fingerprint TLV MUST be included in Link State PDU (LSP) #0
   originated by a router operating in auto-configuration mode.  If an
   LSP #0 which does NOT contain a Router Fingerprint TLV is received by
   a Router operating in auto-configuration mode the LSP is flooded as
   normal, but the entire LSP set originated by the sending router MUST
   be ignored when running the Decision process.

   The router fingerprint TLV MUST NOT be included in an LSP with a non-
   zero number and when received MUST be ignored.

3.4.  Protocol Operation

   This section describes the operation of a router supporting auto-
   configuration mode.

3.4.1.  Start-Up mode

   When a router starts operation in auto-configuration mode, both the S
   and A bits MUST be set in the Router Fingerprint TLV included in both
   hellos and LSP #0.  During this mode only LSP #0 is generated and IS
   or IP/IPv6 reachability TLVs MUST NOT be included in LSP #0.  A
   router remains in Start-up mode for a minimum period of time
   (recommended to be 1 minute).  This time should be sufficient to
   bring up adjacencies to all expected neighbors.  A router leaves
   Start-up mode once the minimum time has elapsed and full LSP database
   synchronization is achieved with all neighbors in the UP state.

   When a router exits startup-mode it clears the S bit in Router
   Fingerprint TLVs it sends in hellos and LSP#0.  The router MAY now
   advertise IS neighbor and IP/IPv6 prefix reachability in its LSPs and
   MAY generate LSPs with a non-zero number.

   The purpose of Start-up Mode is to minimize the occurrence of System
   ID changes for a router once it has become fully operational.  Any
   System ID change during Start-up mode will have minimal impact on a
   running network because while in Start-up mode the router is not yet
   being used for forwarding traffic.

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3.4.2.  Adjacency Formation

   Routers operating in auto-configuration mode MUST NOT form
   adjacencies with routers which are NOT operating in auto-
   configuration mode.  The presence of the Router Fingerprint TLV with
   the A bit set indicates the router is operating in auto-configuration

   NOTE: The use of the special area address of all 0's makes it
   unlikely that a router which is not operating in auto-configuration
   mode will be in the same area as a router operating in auto-
   configuration mode.  However, the check for the Router Fingerprint
   TLV with A bit set provides additional protection.

3.4.3.  IS-IS System ID Duplication Detection

   The System ID of each node MUST be unique.  As described in
   Section 3.4.5, the System ID is generated based on entropies (e.g.
   MAC address) which are generally expected to be unique.  However,
   since there may be limitations to the available entropies, there is
   still the possibility of System ID duplication.  This section defines
   how IS-IS detects and resolves System ID duplication.  Duplicate
   System ID may occur between neighbors or between routers in the same
   area which are not neighbors.

   Duplicate System ID with a neighbor is detected when the System ID
   received in an IIH is identical to the local System ID and the
   Router-Fingerprint in the received Router-Fingerprint TLV does NOT
   match the locally generated Router-Fingerprint.

   Duplicate System ID with a non-neighbor is detected when an LSP #0 is
   received, the System ID of the originator is identical to the local
   System ID, and the Router-Fingerprint in the Router-Fingerprint TLV
   does NOT match the locally generated Router-Fingerprint.

3.4.4.  Duplicate System ID Resolution Procedures

   When duplicate System ID is detected one of the systems MUST assign
   itself a different System ID and perform a protocol restart.  The
   resolution procedure attempts to minimize disruption to a running
   network by choosing a router which is in Start-up mode to be
   restarted whenever possible.

   The contents of the Router-Fingerprint TLVs for the two routers with
   duplicate System IDs are compared.

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   If one TLV has the S bit set (router is in Start-up mode) and one TLV
   has the S bit clear (router is NOT in Start-up mode) the router in
   Start-up mode MUST generate a new System ID and restart the protocol.

   If both TLVs have the S bit set (both routers are in Start-up mode)
   or both TLVs have the S bit clear (neither router is in Start-up
   mode) then the router with numerically smaller Router-Fingerprint
   MUST generate a new System ID and restart the protocol.

   Fingerprint comparison is performed octet by octet starting from the
   first received octet until a difference is detected.  If the
   fingerprints have different lengths and all octets up to the shortest
   length are identical then the fingerprint with smaller length is
   considered smaller.

   If the fingerprints are identical in both content and length (and
   state of the S bit is identical) and the duplication is detected in
   hellos then the both routers MUST generate a new System ID and
   restart the protocol.

   If fingerprints are identical in both content and length and the
   duplication is detected in LSP #0 then the procedures defined in
   Section 3.4.6 MUST be followed.

3.4.5.  System ID and Router-Fingerprint Generation Considerations

   As specified in this document, there are two distinguishing items
   that need to be self-generated: the System ID and Router-Fingerprint.
   In a network device, normally there are some resources which can
   provide an extremely high probability of uniqueness (some examples
   listed below).  These resources can be used as seeds to derive

   o  MAC address(es)

   o  Configured IP address(es)

   o  Hardware IDs (e.g.  CPU ID)

   o  Device serial number(s)

   o  System clock at a certain specific time

   o  Arbitrary received packet(s) on an interface(s)

   This document recommends the use of an IEEE 802 48-bit MAC address
   associated with the router as the initial System ID.  This document

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   does not specify a specific method to re-generate the System ID when
   duplication happens.

   This document also does not specify a specific method to generate the

   There is an important concern that the seeds listed above (except MAC
   address) might not be available in some small devices such as home
   routers.  This is because of hardware/software limitations and the
   lack of sufficient communication packets at the initial stage in home
   routers when doing ISIS auto-configuration.  In this case, this
   document suggests using the MAC address as System ID and generating a
   pseudo-random number based on another seed (such as the memory
   address of a certain variable in the program) as the Router-
   Fingerprint.  The pseudo-random number might not have a very high
   probability of uniqueness in this solution, but should be sufficient
   in home networks scenarios.

   The considerations surrounding System ID stability described in
   section Section 3.2 also need to be applied.

3.4.6.  Duplication of both System ID and Router-Fingerprint

   As described above, the resources for generating System ID/
   Fingerprint might be very constrained during the initial stages.
   Hence, the duplication of both System ID and Router-Fingerprint needs
   to be considered.  In such a case it is possible that a router will
   receive an LSP with System ID and Router-Fingerprint identical to the
   local values but the LSP is NOT identical to the locally generated
   copy i.e. sequence number is newer or sequence number is the same but
   the LSP has a valid checksum which does not match.  The term DD-LSP
   is used to describe such an LSP.

   In a benign case, this will occur if a router restarts and it
   receives copies of its own LSPs from its previous incarnation.  This
   benign case needs to be distinguished from the pathological case
   where there are two different routers with the same System ID and the
   same Router-Fingerprint.

   In the benign case, the restarting router will generate a new version
   of its own LSP with higher sequence number and flood the new LSP
   version.  This will cause other routers in the network to update
   their LSPDB and synchronization will be achieved.

   In the pathological case the generation of a new version of an LSP by
   one of the "twins" will cause the other twin to generate the same LSP
   with a higher sequence number - and oscillation will continue without
   achieving LSPDB synchronization.

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   Note that comparison of S bit in the Router-Fingerprint TLV cannot be
   performed as in the benign case it is expected that the S bit will be
   clear.  Also note that the conditions for detecting duplicate System
   ID will NOT be satisfied because both the System ID and the Router-
   Fingerprint will be identical.

   The following procedure is defined:

       DD-state is a boolean which indicates if a
         DD-LSP #0 has been received
       DD-count is the count of the number of occurences
         of reception of a DD-LSP
       DD-timer is a timer associated with reception of
        DD-LSPs. Recommended value is 60 seconds.
       DD-max is the maximum number of DD-LSPs allowed
        to be received in DD-timer interval.
        Recommended value is 3.

   When a DD-LSP is received:

     If DD-state is FALSE:
       DD-state is set to TRUE
       DD-timer is started
       DD-count is initialized to 1.

     If DD-state is TRUE:
       DD-count is incremented
       If DD-count is >= DD-max:
          Local system MUST generate a new System ID
           and Router-Fingerprint and restart the protocol
          DD-state is (re)initialized to FALSE and
           DD-timer cancelled.

     If DD-timer expires:
       DD-state is set to FALSE.

   Note that to minimze the likelihood of duplication of both System ID
   and Router-fingerprint reoccuring, routers SHOULD have more entropies
   available.  One simple way to achieve this is to add the LSP sequence
   number of the next LSP it will send to the Router-Fingerprint.

3.5.  Additional IS-IS TLVs Usage Guidelines

   This section describes the behavior of selected TLVs when used by a
   router supporting IS-IS auto-configuration.

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3.5.1.  Authentication TLV

   It is RECOMMENDED that IS-IS routers supporting this specification
   offer an option to explicitly configure a single password for HMAC-
   MD5 authentication as specified in[RFC5304].

3.5.2.  Metric Used in Reachability TLVs

   It is RECOMMENDED that IS-IS auto-configuration routers use a high
   metric value (e.g. 100000) as default in order to allow manually
   configured adjacencies to be preferred over auto-configured.

3.5.3.  Dynamic Host Name TLV

   IS-IS auto-configuration routers MAY advertise their Dynamic Host
   Name TLV (TLV 137, [RFC5301]).  The host name could be provisioned by
   an IT system, or just use the name of vendor, device type or serial
   number, etc.

   To guarantee the uniqueness of the host name, the System ID SHOULD be
   appended as a suffix in the names.

4.  Security Considerations

   In the absence of cryptographic authentication it is possible for an
   attacker to inject a PDU falsely indicating there is a duplicate
   system-id.  This may trigger automatic restart of the protocol using
   the duplicate-id resolution procedures defined in this document.

   Note that the use of authentication is incompatible with auto-
   configuration as it requires some manual configuration.

   For wired deployment, the wired connection itself could be considered
   as an implicit authentication in that unwanted routers are usually
   not able to connect (i.e. there is some kind of physical security in
   place preventing the connection of rogue devices); for wireless
   deployment, the authentication could be achieved at the lower
   wireless link layer.

5.  IANA Considerations

   This document requires the definition of a new IS-IS TLV to be
   reflected in the "IS-IS TLV Codepoints" registry:

   Type  Description                       IIH LSP SNP Purge
   ----  ------------                      --- --- --- -----
   TBA   Router-Fingerprint                 Y   Y   N    Y

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6.  Acknowledgements

   This document was heavily inspired by [RFC7503].

   Martin Winter, Christian Franke and David Lamparter gave essential
   feedback to improve the technical design based on their
   implementation experience.

   Many useful comments were made by Acee Lindem, Karsten Thomann,
   Hannes Gredler, Peter Lothberg, Uma Chundury, Qin Wu, Sheng Jiang and
   Nan Wu, etc.

   This document was produced using the xml2rfc tool [RFC7991].
   (initially prepared using  )

7.  References

7.1.  Normative References

              "Intermediate system to Intermediate system intra-domain
              routeing information exchange protocol for use in
              conjunction with the protocol for providing the
              connectionless-mode Network Service (ISO 8473), ISO/IEC
              10589:2002, Second Edition.", Nov 2002.

   [RFC1195]  Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
              dual environments", RFC 1195, DOI 10.17487/RFC1195,
              December 1990, <>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC5301]  McPherson, D. and N. Shen, "Dynamic Hostname Exchange
              Mechanism for IS-IS", RFC 5301, DOI 10.17487/RFC5301,
              October 2008, <>.

   [RFC5304]  Li, T. and R. Atkinson, "IS-IS Cryptographic
              Authentication", RFC 5304, DOI 10.17487/RFC5304, October
              2008, <>.

   [RFC5305]  Li, T. and H. Smit, "IS-IS Extensions for Traffic
              Engineering", RFC 5305, DOI 10.17487/RFC5305, October
              2008, <>.

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   [RFC5308]  Hopps, C., "Routing IPv6 with IS-IS", RFC 5308,
              DOI 10.17487/RFC5308, October 2008,

7.2.  Informative References

   [RFC7503]  Lindem, A. and J. Arkko, "OSPFv3 Autoconfiguration",
              RFC 7503, DOI 10.17487/RFC7503, April 2015,

   [RFC7991]  Hoffman, P., "The "xml2rfc" Version 3 Vocabulary",
              RFC 7991, DOI 10.17487/RFC7991, December 2016,

Authors' Addresses

   Bing Liu (editor)
   Huawei Technologies
   Q10, Huawei Campus, No.156 Beiqing Road
   Hai-Dian District, Beijing, 100095
   P.R. China


   Les Ginsberg
   Cisco Systems
   821 Alder Drive
   Milpitas  CA 95035


   Bruno Decraene


   Ian Farrer
   Deutsche Telekom AG


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   Mikael Abrahamsson


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