Movatterモバイル変換

Internet Engineering Task Force (IETF)                  L. Ginsberg, Ed.Request for Comments: 7794                                 Cisco SystemsCategory: Standards Track                                    B. DecraeneISSN: 2070-1721                                                   Orange                                                              S. Previdi                                                           Cisco Systems                                                                   X. Xu                                                                  Huawei                                                             U. Chunduri                                                                Ericsson                                                              March 2016IS-IS Prefix Attributes for Extended IPv4 and IPv6 ReachabilityAbstract   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 inSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc7794.Ginsberg, et al.             Standards Track                    [Page 1]

RFC 7794                 IS-IS Prefix Attributes              March 2016Copyright Notice   Copyright (c) 2016 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 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 Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .31.1.  Requirements Language . . . . . . . . . . . . . . . . . .32.  New Sub-TLVs for Extended Reachability TLVs . . . . . . . . .32.1.  IPv4/IPv6 Extended Reachability Attribute Flags . . . . .42.2.  IPv4/IPv6 Source Router ID  . . . . . . . . . . . . . . .52.3.  Advertising Router IDs  . . . . . . . . . . . . . . . . .63.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .64.  Security Considerations . . . . . . . . . . . . . . . . . . .75.  References  . . . . . . . . . . . . . . . . . . . . . . . . .75.1.  Normative References  . . . . . . . . . . . . . . . . . .75.2.  Informative References  . . . . . . . . . . . . . . . . .8   Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .8   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .9Ginsberg, et al.             Standards Track                    [Page 2]

RFC 7794                 IS-IS Prefix Attributes              March 20161.  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 inRFC 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 IDGinsberg, 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 inSection 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 inSection 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 advertisementGinsberg, 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 inSection 2.2 is one such use case.   Therefore, whenever an IPv4 or IPv6 Source Router ID sub-TLV (as   defined inSection 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 20164.  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.  References5.1.  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.comGinsberg, et al.             Standards Track                    [Page 8]

RFC 7794                 IS-IS Prefix Attributes              March 2016Authors' 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.comGinsberg, et al.             Standards Track                    [Page 9]