GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


rfc:rfc7794

Internet Engineering Task Force (IETF) L. Ginsberg, Ed. Request for Comments: 7794 Cisco Systems Category: Standards Track B. Decraene ISSN: 2070-1721 Orange

                                                            S. Previdi
                                                         Cisco Systems
                                                                 X. Xu
                                                                Huawei
                                                           U. Chunduri
                                                              Ericsson
                                                            March 2016
  IS-IS Prefix Attributes for Extended IPv4 and IPv6 Reachability

Abstract

 This document introduces new sub-TLVs to support advertisement of
 IPv4 and IPv6 prefix attribute flags and the source router ID of the
 router that originated a prefix advertisement.

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc7794.

Ginsberg, et al. Standards Track [Page 1] RFC 7794 IS-IS Prefix Attributes March 2016

Copyright Notice

 Copyright (c) 2016 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
 (http://trustee.ietf.org/license-info) 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
   1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
 2.  New Sub-TLVs for Extended Reachability TLVs . . . . . . . . .   3
   2.1.  IPv4/IPv6 Extended Reachability Attribute Flags . . . . .   4
   2.2.  IPv4/IPv6 Source Router ID  . . . . . . . . . . . . . . .   5
   2.3.  Advertising Router IDs  . . . . . . . . . . . . . . . . .   6
 3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
 4.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
 5.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
   5.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
   5.2.  Informative References  . . . . . . . . . . . . . . . . .   8
 Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .   8
 Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

Ginsberg, et al. Standards Track [Page 2] RFC 7794 IS-IS Prefix Attributes March 2016

1. Introduction

 IS-IS is a link-state routing protocol defined in [ISO10589] and
 [RFC1195].  Extensions in support of advertising new forms of
 IPv4/IPv6 prefix reachability are defined in [RFC5305], [RFC5308],
 and [RFC5120].
 There are existing use cases in which knowing additional attributes
 of a prefix is useful.
 It is useful to know whether or not an advertised prefix is directly
 connected to the advertising router.  In the case of Segment Routing
 as described in [SR], knowing whether or not a prefix is directly
 connected determines what action should be taken as regards
 processing of labels associated with an incoming packet.
 It is useful to know what addresses can be used as addresses of the
 node in support of services (e.g., Remote Loop Free Alternate (RLFA)
 endpoint).
 Current formats of the Extended Reachability TLVs for both IPv4 and
 IPv6 are fixed and do not allow the introduction of additional flags
 without backwards compatibility issues.  Therefore, this document
 defines a new sub-TLV that supports the advertisement of attribute
 flags associated with prefix advertisements.
 In cases where multiple node addresses are advertised by a given
 router, it is also useful to be able to associate all of these
 addresses with a single Router ID even when prefixes are advertised
 outside of the area in which they originated.  Therefore, a new sub-
 TLV is introduced to advertise the Router ID of the originator of a
 prefix advertisement.

1.1. Requirements Language

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in RFC 2119 [RFC2119].

2. New Sub-TLVs for Extended Reachability TLVs

 The following new sub-TLVs are introduced:
 o  Prefix Attribute Flags
 o  IPv4 Source Router ID
 o  IPv6 Source Router ID

Ginsberg, et al. Standards Track [Page 3] RFC 7794 IS-IS Prefix Attributes March 2016

 All sub-TLVs are applicable to TLVs 135, 235, 236, and 237.

2.1. IPv4/IPv6 Extended Reachability Attribute Flags

 This sub-TLV supports the advertisement of additional flags
 associated with a given prefix advertisement.  The behavior of each
 flag when a prefix advertisement is leaked from one level to another
 (upwards or downwards) is explicitly defined below.
 All flags are applicable to TLVs 135, 235, 236, and 237, unless
 otherwise stated.
   Prefix Attribute Flags
   Type:   4
   Length: Number of octets of the Value field.
   Value:
        (Length * 8) bits.
     0 1 2 3 4 5 6 7...
    +-+-+-+-+-+-+-+-+...
    |X|R|N|          ...
    +-+-+-+-+-+-+-+-+...
 Bits are defined/sent starting with Bit 0 defined below.  Additional
 bit definitions that may be defined in the future SHOULD be assigned
 in ascending bit order so as to minimize the number of bits that will
 need to be transmitted.
 Undefined bits MUST be transmitted as 0 and MUST be ignored on
 receipt.
 Bits that are NOT transmitted MUST be treated as if they are set to 0
 on receipt.
 X-Flag:  External Prefix Flag (Bit 0)
    Set if the prefix has been redistributed from another protocol.
    This includes the case where multiple virtual routers are
    supported and the source of the redistributed prefix is another
    IS-IS instance.
    The flag MUST be preserved when leaked between levels.
    In TLVs 236 and 237, this flag SHOULD always be sent as 0 and MUST
    be ignored on receipt.  This is because there is an existing X
    flag defined in the fixed format of these TLVs as specified in
    [RFC5308] and [RFC5120].

Ginsberg, et al. Standards Track [Page 4] RFC 7794 IS-IS Prefix Attributes March 2016

 R-Flag:  Re-advertisement Flag (Bit 1)
    Set when the prefix has been leaked from one level to another
    (upwards or downwards).
 N-flag:  Node Flag (Bit 2)
    Set when the prefix identifies the advertising router, i.e., the
    prefix is a host prefix advertising a globally reachable address
    typically associated with a loopback address.
    The advertising router MAY choose to NOT set this flag even when
    the above conditions are met.
    If the flag is set and the prefix length is NOT a host prefix (/32
    for IPV4, /128 for IPv6), then the flag MUST be ignored.  The flag
    MUST be preserved when leaked between levels.

2.2. IPv4/IPv6 Source Router ID

 When a reachability advertisement is leaked from one level to
 another, the source of the original advertisement is unknown.  In
 cases where the advertisement is an identifier for the advertising
 router (e.g., with the N-flag set in the Prefix Attribute Flags sub-
 TLV as described in Section 2.1), it may be useful for other routers
 to know the source of the advertisement.  The sub-TLVs defined below
 provide that information.
 Note that the Router ID advertised is always the Router ID of the
 IS-IS instance that originated the advertisement.  This would be true
 even if the prefix had been learned from another protocol (i.e., with
 the X-flag set as defined in Section 2.1).
   IPv4 Source Router ID
   Type:   11
   Length: 4
   Value:  IPv4 Router ID of the source of the advertisement
 Inclusion of this TLV is optional and MAY occur in TLVs 135, 235,
 236, or 237.  When included, the value MUST be identical to the value
 advertised in the Traffic Engineering router ID (TLV 134) defined in
 [RFC5305].
 If present the sub-TLV MUST be included when the prefix advertisement
 is leaked to another level.
   IPv6 Source Router ID
   Type:   12
   Length: 16
   Value: IPv6 Router ID of the source of the advertisement

Ginsberg, et al. Standards Track [Page 5] RFC 7794 IS-IS Prefix Attributes March 2016

 Inclusion of this TLV is optional and MAY occur in TLVs 135, 235,
 236, or 237.  When included, the value MUST be identical to the value
 advertised in the IPv6 TE Router ID (TLV 140) defined in [RFC6119].
 If present, the sub-TLV MUST be included when the prefix
 advertisement is leaked to another level.

2.3. Advertising Router IDs

 [RFC5305] and [RFC6119] define the advertisement of router IDs for
 IPv4 and IPv6, respectively.  Although both documents discuss the use
 of router ID in the context of Traffic Engineering (TE), the
 advertisement of router IDs is explicitly allowed for purposes other
 than TE.  The use of router IDs to identify the source of a prefix
 advertisement as defined in Section 2.2 is one such use case.
 Therefore, whenever an IPv4 or IPv6 Source Router ID sub-TLV (as
 defined in Section 2.2) is used, the originating router SHOULD also
 advertise the corresponding address-family-specific router ID TLV.

3. IANA Considerations

 This document adds the following new sub-TLVs to the registry of sub-
 TLVs for TLVs 135, 235, 236, and 237.
    Value: 4
    Name: Prefix Attribute Flags
    Value: 11
    Name: IPv4 Source Router ID
    Value: 12
    Name: IPv6 Source Router ID
 This document also introduces a new registry for bit values in the
 Prefix Attribute Flags sub-TLV.  The registration policy is Expert
 Review as defined in [RFC5226].  This registry is part of the "IS-IS
 TLV Codepoints" registry.  The name of the registry is "Bit Values
 for Prefix Attribute Flags Sub-TLV".  The defined values are:
      Bit #   Name
      -----   ------------------------------
      0       External Prefix Flag (X-flag)
      1       Re-advertisement Flag (R-flag)
      2       Node Flag (N-flag)

Ginsberg, et al. Standards Track [Page 6] RFC 7794 IS-IS Prefix Attributes March 2016

4. Security Considerations

 Security concerns for IS-IS are addressed in [RFC5304] and [RFC5310].
 Advertisement of the additional information defined in this document
 introduces no new security concerns.

5. References

5.1. Normative References

 [ISO10589] International Organization for Standardization,
            "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, <http://www.rfc-editor.org/info/rfc1195>.
 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119,
            DOI 10.17487/RFC2119, March 1997,
            <http://www.rfc-editor.org/info/rfc2119>.
 [RFC5120]  Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
            Topology (MT) Routing in Intermediate System to
            Intermediate Systems (IS-ISs)", RFC 5120,
            DOI 10.17487/RFC5120, February 2008,
            <http://www.rfc-editor.org/info/rfc5120>.
 [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
            IANA Considerations Section in RFCs", BCP 26, RFC 5226,
            DOI 10.17487/RFC5226, May 2008,
            <http://www.rfc-editor.org/info/rfc5226>.
 [RFC5304]  Li, T. and R. Atkinson, "IS-IS Cryptographic
            Authentication", RFC 5304, DOI 10.17487/RFC5304, October
            2008, <http://www.rfc-editor.org/info/rfc5304>.
 [RFC5305]  Li, T. and H. Smit, "IS-IS Extensions for Traffic
            Engineering", RFC 5305, DOI 10.17487/RFC5305, October
            2008, <http://www.rfc-editor.org/info/rfc5305>.

Ginsberg, et al. Standards Track [Page 7] RFC 7794 IS-IS Prefix Attributes March 2016

 [RFC5308]  Hopps, C., "Routing IPv6 with IS-IS", RFC 5308,
            DOI 10.17487/RFC5308, October 2008,
            <http://www.rfc-editor.org/info/rfc5308>.
 [RFC5310]  Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
            and M. Fanto, "IS-IS Generic Cryptographic
            Authentication", RFC 5310, DOI 10.17487/RFC5310, February
            2009, <http://www.rfc-editor.org/info/rfc5310>.
 [RFC6119]  Harrison, J., Berger, J., and M. Bartlett, "IPv6 Traffic
            Engineering in IS-IS", RFC 6119, DOI 10.17487/RFC6119,
            February 2011, <http://www.rfc-editor.org/info/rfc6119>.

5.2. Informative References

 [SR]       Previdi, S., Ed., Filsfils, C., Bashandy, A., Gredler, H.,
            Litkowski, S., Decraene, B., and J. Tantsura, "IS-IS
            Extensions for Segment Routing", Work in Progress,
            draft-ietf-isis-segment-routing-extensions-06, December
            2015.

Contributors

 The following people gave a substantial contribution to the content
 of this document:
 Clarence Filsfils
 Cisco Systems
 Email: cf@cisco.com
 Stephane Litkowski
 Orange Business Service
 Email: stephane.litkowski@orange.com

Ginsberg, et al. Standards Track [Page 8] RFC 7794 IS-IS Prefix Attributes March 2016

Authors' Addresses

 Les Ginsberg (editor)
 Cisco Systems
 510 McCarthy Blvd.
 Milpitas, CA  95035
 United States
 Email: ginsberg@cisco.com
 Bruno Decraene
 Orange
 38 rue du General Leclerc
 Issy Moulineaux cedex 9  92794
 France
 Email: bruno.decraene@orange.com
 Stefano Previdi
 Cisco Systems
 Via Del Serafico 200
 Rome  0144
 Italy
 Email: sprevidi@cisco.com
 Xiaohu Xu
 Huawei
 Email: xuxiaohu@huawei.com
 Uma Chunduri
 Ericsson
 Email: uma.chunduri@ericsson.com

Ginsberg, et al. Standards Track [Page 9]

/data/webs/external/dokuwiki/data/pages/rfc/rfc7794.txt · Last modified: 2016/03/03 19:32 by 127.0.0.1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki