Internet DRAFT - draft-ietf-isis-genapp
draft-ietf-isis-genapp
Network Working Group L. Ginsberg
Internet-Draft S. Previdi
Intended status: Standards Track M. Shand
Expires: May 14, 2011 Cisco Systems
November 10, 2010
Advertising Generic Information in IS-IS
draft-ietf-isis-genapp-04.txt
Abstract
This draft describes the manner in which generic application
information (i.e. information not directly related to the operation
of the IS-IS protocol) should be advertised in IS-IS LSPs and defines
guidelines which should be used when flooding such information.
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
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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."
This Internet-Draft will expire on May 14, 2011.
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
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described in the Simplified BSD License.
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Table of Contents
1. Conventions used in this Document . . . . . . . . . . . . . . 3
2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Encoding Format for GENINFO . . . . . . . . . . . . . . . . . 3
3.1. GENINFO TLV . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Use of sub-TLVs in GENINFO TLV . . . . . . . . . . . . . . 6
4. GENINFO Flooding Procedures . . . . . . . . . . . . . . . . . 6
4.1. Leaking Procedures . . . . . . . . . . . . . . . . . . . . 7
4.2. Minimizing Update Confusion . . . . . . . . . . . . . . . 7
4.3. Interpreting Attribute Information . . . . . . . . . . . . 8
5. Use of a Separate Protocol Instance . . . . . . . . . . . . . 8
6. Applicability of GENINFO TLV . . . . . . . . . . . . . . . . . 9
7. Standardization Requirements . . . . . . . . . . . . . . . . . 9
8. Security Considerations . . . . . . . . . . . . . . . . . . . 9
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
11. Normative References . . . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
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1. Conventions used in this Document
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 [RFC2119].
2. Overview
[ISO10589] defines the format of type-length-value (TLVs) which may
be sent in IS-IS Protocol Data Units (PDUs). The first octet of a
TLV encodes the "type" or "codepoint" which provides a scope for the
information and information format which follows. The protocol is
therefore limited to 256 different codepoints which may be assigned.
This number has proved generous as regards the information required
for correct operation of the Intermediate System to Internediate
System (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
which has the potential to consume a significant number of TLV
codepoints. This document therefore defines an encoding format for
GENINFO which minimizes the consumption of TLV codepoints and also
maximizes the flexibility of the formats which 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 which generates/consumes the GENINFO is outside the scope
of this specification.
In order to minimize the impact 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
[I-D.ietf-isis-mi] except where the rules for the use of the zero
instance set out later in this document are followed.
3. Encoding Format for GENINFO
The encoding format defined below has the following goals regarding
the advertisement of GENINFO in IS-IS LSPs:
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o Minimize the number of IS-IS top level and sub-TLV codepoints
required
o Minimize the depth of sub-TLV levels required
In order to support these goals, a new IANA registry is required.
This registry will manage the assignment of IS-IS GENINFO Application
Identifiers. These numbers are unsigned 16 bit numbers ranging in
value from 1 to 65535. Application specific sub-TLV codepoints are
unsigned 8 bit numbers ranging in value from 0 to 255. The
assignment of the sub-TLV codepoints is scoped by the Application
Identifier. Management of the application specific sub-TLV
codepoints is outside the scope of this document.
3.1. GENINFO TLV
The GENINFO TLV supports the advertisement of application specific
information which is not directly related to the operation of the
IS-IS protocol.
Type 251
Length # of octets in the value field (3 to 255)
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.
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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.
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3.2. Use of sub-TLVs in GENINFO TLV
[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 which 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 which 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.
4. GENINFO Flooding Procedures
This section describes procedures which apply to the propagation of
LSPs which contain GENINFO TLVs. These procedures have been
previously discussed in [RFC4971]. This section is intended to serve
as a reference specification for future documents which 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 which have different flooding scopes, a
router MUST originate a minimum of one GENINFO TLV for each required
flooding scope. GENINFO TLVs which contain information having area/
level scope will have the S bit clear. These TLVs MUST NOT be leaked
into another level. GENINFO TLVs which contain information which 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.
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4.1. Leaking Procedures
When leaking GENINFO TLVs downward from Level-2 into Level-1, if the
originator of the TLV is a Level-1 router in another area, it is
possible that multiple copies of the same TLV may be received from
multiple L2 routers in the originating area. A router performing
downward leaking MUST check for such duplication by comparing the
contents of the TLVs. The set of LSPs generated by a router for a
given level MUST NOT contain two or more copies of the same GENINFO
TLV.
In order to prevent the use of stale GENINFO information, a system
MUST NOT use a GENINFO TLV present in an LSP of a system which is not
currently reachable via Level-x paths, where "x" is the level (1 or
2) associated with the LSP in which the GENINFO TLV appears. Note
that leaking a GENINFO TLV is one of the uses which is prohibited
under these conditions. The following example illustrates what might
occur in the absence of this restriction.
Example: If Level-1 router A generates a GENINFO TLV and floods it to
two L1/L2 routers S and T, they will flood it into the Level-2 sub-
domain. Now suppose the Level-1 area partitions, such that A and S
are in one partition and T is in another. IP routing will still
continue to work, but if A now issues a revised version of the
GENINFO TLV, or decides to stop advertising it, S will follow suit,
but T will continue to advertise the old version until the LSP times
out.
Routers in other areas have to choose whether to trust T's copy of
A's GENINFO TLV or S's copy of A's information and they have no
reliable way to choose. By making sure that T stops leaking A's
information, this removes the possibility that other routers will use
stale information from A.
4.2. Minimizing Update Confusion
If an update to a TLV is advertised in an LSP with a different number
than the LSP associated with the old advertisement, the possibility
exists that other systems can temporarily have either 0 copies of a
particular advertisement or 2 copies of a particular advertisement,
depending on the order in which new copies of the LSP which had the
old advertisement and the LSP which has the new advertisement arrive
at other systems.
Whenever possible, an implementation SHOULD advertise the update to a
GENINFO TLV in the LSP with the same number as the advertisement
which it replaces. Where this is not possible, the two affected LSPs
SHOULD be flooded as an atomic action.
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Systems which receive an update to an existing GENINFO TLV can
minimize the potential disruption associated with the update by
employing a holddown time prior to processing the update so as to
allow for the receipt of multiple LSPs associated with the same
update prior to beginning processing.
4.3. Interpreting Attribute Information
Where a receiving system has two copies of a GENINFO TLV with the
same Application ID, attribute information in the two TLVs which does
not conflict MUST be considered additive. When information in the
two GENINFO TLVs conflicts i.e there are different settings for a
given attribute, the procedure used to choose which copy shall be
used is undefined.
5. Use of a Separate Protocol Instance
The use of the IS-IS flooding mechanism as a means of reliably and
efficiently propagating information is understandably attractive.
However, it is prudent to remember that the primary purpose of that
mechanism is to flood information necessary for the correct operation
of the IS-IS protocol. Flooding of information not directly related
to the use of the IS-IS protocol in support of routing degrades the
operation of the protocol. Degradation occurs because the frequency
of LSP updates is increased and because the processing of non-routing
information in each router consumes resources whose primary
responsibility is to efficiently respond to reachability changes in
the network.
Advertisement of GENINFO therefore MUST occur in the context of a
non-zero instance of the IS-IS protocol as defined in
[I-D.ietf-isis-mi] 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, which can lead to flooding storms. Documents which
specify the use of the mechanisms defined here MUST define the
expected rate of change of the information to be advertised.
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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.[I-D.ietf-isis-mi].
6. Applicability of GENINFO TLV
The GENINFO TLV supports the advertisement of application specific
information in IS-IS LSPs which is not directly related to the
operation of the IS-IS protocol. Information advertised in the
GENINFO TLV MUST NOT alter basic IS-IS protocol operation including
(but not limited to) the establishment of adjacencies, the update
process, and the decision process.
7. Standardization Requirements
GENINFO is intended to advertise information on behalf of
applications whose operations have been defined in a public
specification as discussed in [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
8. Security Considerations
The introduction and use of the new TLV codepoint for GENINFO in and
of itself raises no new security issues for IS-IS.
It is possible that information advertised in a GENINFO TLV by a
given Application MAY introduce new security issues. The public
specification which defines the use of GENINFO by that Application
MUST include a discussion of the security issues. Where appropriate,
it is recommended that either [RFC5304] or [RFC5310] be used.
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9. IANA Considerations
This document defines a new IS-IS TLV that needs to be reflected in
the IS-IS TLV code-point registry:
Type Description IIH LSP SNP
---- ----------------------------------- --- --- ---
251 Generic Information n y n
This document also defines a new registry. The new registry will
manage the assignment of Application Identifiers which may be used in
the Generic Information TLV. These identifiers are unsigned 16 bit
numbers ranging in value from 1 to 65535. The value 0 is reserved.
Registration procedure is "Expert Review" as defined in [RFC5226].
The expert MUST verify that the public specification which 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
10. Acknowledgements
The authors would like to thank JP Vasseur and David Ward for
providing the need to produce this document and Tony Li for making
sure it was done with appropriate wisdom and prudence.
11. Normative References
[I-D.ietf-isis-mi]
Previdi, S., Ginsberg, L., Shand, M., Ward, D., and A.
Roy, "IS-IS Multi-Instance", draft-ietf-isis-mi-03 (work
in progress), July 2010.
[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
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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.
Authors' Addresses
Les Ginsberg
Cisco Systems
510 McCarthy Blvd.
Milpitas, Ca. 95035
USA
Email: ginsberg@cisco.com
Stefano Previdi
Cisco Systems
Via Del Serafico 200
00142 - Roma,
Italy
Email: sprevidi@cisco.com
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Mike Shand
Cisco Systems
250, Longwater Avenue.
Reading, Berks RG2 6GB
UK
Email: mshand@cisco.com
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