Internet Engineering Task Force (IETF) L. Ginsberg Request for Comments: 6823 S. Previdi Category: Standards Track M. Shand ISSN: 2070-1721 Cisco Systems December 2010 Advertising Generic Information in IS-IS
AbstractThis document describes the manner in which generic application information (i.e., information not directly related to the operation of the Intermediate System to Intermediate System (IS-IS) protocol) should be advertised in IS-IS Link State Protocol Data Units (LSPs) and defines guidelines that should be used when flooding such information. 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/rfc6823. Copyright Notice Copyright (c) 2010 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.
1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Conventions Used in This Document . . . . . . . . . . . . . . 3 3. Encoding Format for GENINFO . . . . . . . . . . . . . . . . . 3 3.1. GENINFO TLV . . . . . . . . . . . . . . . . . . . . . . . 3 3.2. Use of Sub-TLVs in GENINFO TLV . . . . . . . . . . . . . . 5 4. GENINFO Flooding Procedures . . . . . . . . . . . . . . . . . 5 4.1. Leaking Procedures . . . . . . . . . . . . . . . . . . . . 6 4.2. Minimizing Update Confusion . . . . . . . . . . . . . . . 7 4.3. Interpreting Attribute Information . . . . . . . . . . . . 7 5. Use of a Separate Protocol Instance . . . . . . . . . . . . . 7 6. Applicability of GENINFO TLV . . . . . . . . . . . . . . . . . 8 7. Standardization Requirements . . . . . . . . . . . . . . . . . 8 8. Security Considerations . . . . . . . . . . . . . . . . . . . 9 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9 11. Normative References . . . . . . . . . . . . . . . . . . . . . 10 ISO10589] defines the format of Type-Length-Values (TLVs) that may be sent in IS-IS Protocol Data Units (PDUs). The first octet of a TLV encodes the "type" or "codepoint" that provides a scope for the information and information format that follows. The protocol is therefore limited to 256 different codepoints that may be assigned. This number has proved generous as regards the information required for correct operation of the IS-IS protocol. However, the increasing use of IS-IS Link State Protocol Data Units (LSPs) for advertisement of generic information (GENINFO) not directly related to the operation of the IS-IS protocol places additional demands on the TLV encoding space that have the potential to consume a significant number of TLV codepoints. This document therefore defines an encoding format for GENINFO that minimizes the consumption of TLV codepoints and also maximizes the flexibility of the formats that can be used to represent GENINFO. This document also discusses optimal behavior associated with the advertisement and flooding of LSPs containing GENINFO in order to avoid the advertisement of stale information and minimize the presence of duplicate or conflicting information when advertisements are updated. The manner in which the information contained in GENINFO TLVs is exchanged between an instance of the IS-IS protocol and the application that generates or consumes the GENINFO is outside the scope of this specification.
In order to minimize the impact that advertisement of GENINFO may have on the operation of routing, such advertisements MUST occur in the context of a non-zero instance of the IS-IS protocol as defined in [RFC6822] except where the rules for the use of the zero instance set out later in this document are followed. RFC2119].
Value: No. of octets +-----------------------+ | Flags | 1 +-----------------------+ | Application ID | 2 +-----------------------+ | Application | | IP Address Info | 0 to 20 +-----------------------+ |Additional Application-| 0 to (252 - | Specific Information | len of IP Address info) +-----------------------+ Flags 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ | Rsvd |V|I|D|S| +-+-+-+-+-+-+-+-+ The following bit flags are defined. S bit (0x01): If the S bit is set (1), the GENINFO TLV MUST be flooded across the entire routing domain. If the S bit is not set (0), the TLV MUST NOT be leaked between levels. This bit MUST NOT be altered during the TLV leaking. D bit (0x02): When the GENINFO TLV is leaked from Level-2 to Level-1, the D bit MUST be set. Otherwise, this bit MUST be clear. GENINFO TLVs with the D bit set MUST NOT be leaked from Level-1 to Level-2. This is to prevent TLV looping. I bit (0x04): When the I bit is set, the 4-octet IPv4 address associated with the application immediately follows the Application ID. V bit (0x08): When the V bit is set, the 16-octet IPv6 address associated with the application immediately follows either the Application ID (if I bit is clear) or the IPv4 address (if I bit is set). Application ID An identifier assigned to this application via the IANA registry defined later in this document.
Application IPv4 Address Info The IPv4 address associated with the application. This is not necessarily an address of a router running the IS-IS protocol. Application IPv6 Address Info The IPv6 address associated with the application. This is not necessarily an address of a router running the IS-IS protocol. Additional Application-Specific Information Each application may define additional information to be encoded in a GENINFO TLV following the fixed information. Definition of such information is beyond the scope of this document. RFC5305] introduced the definition and use of sub-TLVs. One of the advantages of using sub-TLVs rather than fixed encoding of information inside a TLV is to allow for the addition of new information in a backwards compatible manner, i.e., just as with TLVs, implementations are required to ignore sub-TLVs that they do not understand. GENINFO TLVs MAY include sub-TLVs in the application specific information as deemed necessary and appropriate for each application. The scope of the codepoints used in such sub-TLVs is defined by the combination of the GENINFO TLV codepoint and the Application ID, i.e., the sub-TLV codepoints are private to the application. Such sub-TLVs are referred to as APPsub-TLVs. Additional levels of APPsub-TLVs may be required when there is variable information that is scoped by a specific APPsub-TLV. These "nested" sub-TLVs MUST be encoded in the same manner as sub-TLVs, i.e., with a one-octet Type field, a one-octet Length field, and zero or more octets of Value. RFC4971]. This section is intended to serve as a reference specification for future documents that define the use of GENINFO TLV(s) for a specific application -- eliminating the need to repeat the definition of these procedures in the application- specific documents. Each GENINFO TLV contains information regarding exactly one application instance as identified by the Application ID in the GENINFO TLV. When it is necessary to advertise sets of information
with the same Application ID that have different flooding scopes, a router MUST originate a minimum of one GENINFO TLV for each required flooding scope. GENINFO TLVs that contain information having area/ level scope will have the S bit clear. These TLVs MUST NOT be leaked into another level. GENINFO TLVs that contain information that has domain scope will have the S bit set. These TLVs MUST be leaked into other IS-IS levels. When a TLV is leaked from Level-2 to Level-1, the D bit MUST be set in the Level-1 LSP advertisement.
RFC6822] except when the use in the zero instance is defined in a Standards Track RFC.
The use of a separate instance of the protocol allows both the flooding and the processing of the non-routing information to be decoupled from the information necessary to support correct routing of data in the network. The flooding and processing of non-routing information can then be prioritized appropriately. Use of a separate protocol instance to advertise GENINFO does not eliminate the need to use prudence in the frequency with which such information is updated. One of the most egregious oversights is a failure to appropriately dampen changes in the information to be advertised; this can lead to flooding storms. Documents that specify the use of the mechanisms defined here MUST define the expected rate of change of the information to be advertised. If desirable, independent control of the flooding scope for information related to two different applications can be achieved by utilizing separate non-zero protocol instances for each application [RFC6822]. RFC5226]. The public specification MUST include: o a description of the sub-TLV allocation policy o discussion of security issues o discussion of the rate of change of the information being advertised o justification for the use of GENINFO
RFC5304] or [RFC5310] be used. RFC5226]. The expert MUST verify that the public specification that defines the use of GENINFO for the application adequately discusses all points mentioned in Section 7 of this document. The following information MUST be specified in the registry: o ID Value (1-65535) o Description o Allowed in Instance zero (Y/N) o Reference Specification
[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. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC4971] Vasseur, JP., Shen, N., and R. Aggarwal, "Intermediate System to Intermediate System (IS-IS) Extensions for Advertising Router Information", RFC 4971, July 2007. [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 5226, May 2008. [RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic Authentication", RFC 5304, October 2008. [RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic Engineering", RFC 5305, October 2008. [RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R., and M. Fanto, "IS-IS Generic Cryptographic Authentication", RFC 5310, February 2009. [RFC6822] Previdi, S., Ginsberg, L., Shand, M., Roy, A., and D. Ward, "IS-IS Multi-Instance", RFC 6822, December 2012.