Network Working Group Acee Lindem (Redback Networks)
Internet Draft Naiming Shen (Redback Networks)
Expiration Date: August 2004 Rahul Aggarwal (Juniper Networks)
Scott Shaffer (Genuity, Inc.)
Extensions to IS-IS for Advertising Optional
Router Capabilities
draft-raggarwa-isis-cap-01.txt
1. Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026, except that the right to
produce derivative works is not granted.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that other
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The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
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2. Abstract
It is useful for routers in an IS-IS domain to know of the capabilities
of their neighbors, and/or of other routers in the domain. This
draft proposes extensions to IS-IS for advertising optional router
capabilities. In particular it defines an optional Router Capability
TLV for IS-IS.
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3. Motivation
It is useful for routers in a domain to know of the capabilities
of their IS-IS neighbors, and/or of other routers in the domain. This
can be useful for various purposes:
o In MPLS Traffic Engineering (TE) as a TE discovery mechanism
[10] to announce a LSR's TE capabilities like Path Computation
Server capability (Capability of a LSR to be a Path Computation
Server for TE LSP path computation) or the intention of a LSR to be
part of a particular MPLS TE mesh group.
o For network management and troubleshooting. It gives operators a
network wide view of IS-IS capabilities on different routers in the
network. The presence of a capability on a given router implies
that the software version supports the capability and the router is
configured to support it. On the other hand the absence of an
expected capability on a particular router can imply either
mis-configuration or an incorrect software version. Hence this
capability information can be used to track problems resulting from
mis-configuration or an incorrect software version.
There is no existing mechanism in IS-IS to advertise optional router
capabilities. We propose extensions to IS-IS for advertising these
optional capabilities. For current IS-IS capabilities this
advertisement will be used primarily for MPLS TE and informational
purposes. Conceivably, future capability advertisements could be
used for other purposes.
4. IS-IS Router Capability TLV
IS-IS [1] routers may optionally advertise their router
capabilities in the TLV with code type 242. This TLV specifies
the router ID of the router that originates the TLV, defines the
flooding scope of the TLV, specifies the router capability bits in
the first sub-TLV and certain capability related information in other
sub-TLVs. This draft does not specify how an application may use the
Router Capability TLV and such specification is outside the scope of
this draft.
The router ID is a 32 bit unsigned integer to represent the router
that originated this capability TLV. This is needed since this TLV
can be flooded over the entire domain, hence the router ID of the
originating router must be kept.
The capability bits are defined in a mandatory sub-TLV with
code 1. It starts as a 32 bits flag, where each bit can represent
a router capability. This flag can be expanded as needed to
include more capabilities.
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Some of the router capabilities may require more information
than a single bit. The extra capability information can be encoded
as sub-TLVs under this router capability TLV. The definition
of these sub-TLVs is outside the scope of this draft.
If a router does not advertise this TLV, it does not imply that
the router does not support one or more of the defined capabilities.
If this TLV is included in the LSP, the router SHOULD set all
the defined bits corresponding to the capabilities which the
software supports, unless they are explicitly configured off.
4.1 Flooding Scope of the Router Capability TLV
There are three bits currently defined for this TLV in the
information flag to control the flooding scope of the TLV. The
Flooding bit, the Transit bit and the Down bit.
There are two flooding types defined for this router capability
TLV's flooding scope. One is the domain wide flooding scope and
the other is the intra-area flooding scope. The F bit if set
indicates this TLV has the domain wide flooding scope.
The Transit bit can be used to signal the routers on the edge
of the IGP routing domain to redistribute this TLV information
into another routing process. How this is done is an application
specific issue and is outside the scope of this document.
The L1/L2 routers MUST observe the Down bit to avoid TLV leak
looping. This Down bit is not set when the router first originates
this TLV and it MUST be set when leaking into a lower level or into
another area of the same level. When the Down bit is set, this TLV
can no longer be leaked to a higher level or into another area
of the same level. This capability TLV MUST be preserved at the
level boundary during TLV leaking. The L1/L2 router SHOULD
NOT leak the TLV back into the same area which originated
this TLV. It MAY be able to alter certain capability contents
during TLV leaking when specified by applications.
4.2 Encoding of the Router Capability TLV
The following figure depicts the structure of this IS-IS Router
Capability TLV.
x CODE - 242
x LENGTH - total length of the value field in this TLV
x VALUE - 4-octet information flag, 4-octet router ID,
1-octet sub-tlv length, the mandatory sub-TLV code 1
for capability flags, and optional sub-TLVs for extra
capability information, structured as follows:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|F|T|D| Reserved Information Flag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Router ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|sub-TLV Length |Sub-TLV Type(1)| Length | N x 32bits... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Other optional Sub-TLVs.. |
Figure 1. IS-IS Router Capability TLV
The first field is the 4-octet information flag, which consists
of the F, T and D bits, the reserved information bits.
Bit F represents the Flooding scope of the TLV. If set, this TLV
SHOULD be flooded to entire IGP domain. Otherwise, it SHOULD NOT
be leaked into the other level or another area in the same level.
Bit T determines the Transit behavior into other routing domains.
For example, if this bit is set, a router can leak this capability
information into another routing protocol.
Bit D represents Down/Up behavior during the TLV leaking. When the
capability is leaked from level 2 into level 1 or it is leaked into
another area of the same level, this D bit MUST be set. Otherwise
this bit MUST be cleared.
Router ID is an unsigned 32 bit number representing the router
that originates this router capability TLV.
The next octet of the TLV is the total sub-TLV length of this
router capability TLV. This sub-TLV length includes the first
mandatory sub-TLV. The minimum value of this field is 6.
The first sub-TLV with code 1 is a mandatory sub-TLV, the router
capability flag sub-TLV. The length is the length of this sub-TLV.
Its set to N x 4 octets. N starts from 1 and can be increased when
there is a need. Each 4 octets are referred to as a capability flag.
For each capability flag the bits are indexed from the most
significant to the least significant, where each bit represents one
router capability.
There can be other sub-TLVs after the first sub-TLV to include
extra information describing certain router capabilities. The
description of those sub-TLVs is outside the scope of this draft.
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The above data structure can be replicated within this TLV, but
can not exceed the maximum length of 255 octets. If no other
sub-TLVs are used and the capability flag is the minimum 4 octets,
this encoding can contain up to 17 router capability TLVs where
each have a minimum of 15 octets of data(4 byte information flag,
4 byte router-id, 1 byte total sub-tlv length, 6 byte capability
flag).
4.3 Reserved IS-IS Router Capability Bits
We have assigned some pre-determined bits to the first capability
flag.
Bit Capabilities
0-3 Reserved
4 IS-IS graceful restart capable [4]
5 IS-IS and BGP blackhole avoidance capable [6]
6 IS-IS wide metric processing capable [3]
7 IS-IS short metric processing capable [1]
8 IS-IS hmac-md5 authentication capable [5]
9 IS-IS Traffic Engineering support [3]
10 IS-IS point-to-point over LAN [7]
11 IS-IS Path Computation Server discovery [10]
12 M-ISIS capable [8]
13 IS-IS IPv6 capable [9]
14-31 For future assignments
6. Security Consideration
This document does not introduce new security issues. The security
considerations pertaining to the original IS-IS protocol remain
relevant.
7. Acknowledgments
The idea for this work grew out of a conversation with Andrew Partan
and we would like to thank him for his contribution.
8. References
[1] Callon, R., "OSI IS-IS for IP and Dual Environment," RFC 1195,
December 1990.
[2] ISO, "Intermediate system to Intermediate system routeing
information exchange protocol for use in conjunction with the
Protocol for providing the Connectionless-mode Network
Service (ISO 8473)," ISO/IEC 10589:1992.
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[3] Li, T. et al, "IS-IS Extensions for Traffic Engineering",
Internet Draft, work in Progress.
[4] Shand, M., "Restart Signaling for IS-IS", Internet Draft, work
in Progress.
[5] Li, T., "IS-IS Cryptographic Authentication", Internet Draft,
work in progress.
[6] McPherson, D., "IS-IS Transient Blackhole Avoidance", Internet
Draft, work in progress.
[7] N. Shen, et al, "Point-to-point operation over LAN in
link-state-routing protocols", Internet Draft, work in
progress.
[8] T. Przygienda, N. Shen, N. Sheth, "M-ISIS: Multi Topology (MT)
Routing in IS-IS", Internet Draft, work in progress.
[9] C. Hopps, "Routing IPv6 with IS-IS", Internet Draft, work
in progress.
[10] Vasseur et al, "RSVP Path computation request and reply
" messages", draft-vasseur-mpls-computation-rsvp-te-03.txt,
work in progress
9. Author Information
Acee Lindem
Redback Networks
350 Holger Way
San Jose, CA 95134
e-mail: acee@redback.com
Naiming Shen
Redback Networks
350 Holger Way
San Jose, CA 95134
e-mail: naiming@redback.com
Rahul Aggarwal
Juniper Networks
1194 N. Mathilda Avenue
San Jose, CA 94089
e-mail: rahul@juniper.net
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Scott Shaffer
Genuity, Inc.
3 Van de Graaff Drive
PO Box 3073
Burlington, MA 01803
e-mail: sshaffer@genuity.com
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