Network Working Group D. Ward
Internet-Draft Cisco Systems
Expires: January 2, 2006 R. Perlman
Sun Microsystems
R. White
D. Farinacci
Cisco Systems
July 2005
Carrying Attached Addresses in IS-IS
draft-ward-l2isis-00
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Copyright (C) The Internet Society (2005).
Abstract
This draft specifies the IS-IS extensions necessary to support multi-
link IPv4 and IPv6 networks, as well as to provide true link state
routing to any protocols running directly over layer 2. While
supporing this concept involves several pieces, this document only
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describes extensions to IS-IS. We leave it to the systems using
these IS-IS extensions to explain how the information carried in
IS-IS is used.
1. Overview
There are a number of systems which have proposed using layer 2
addresses carried in a link state routing protocol, specifically
IS-IS [IS-IS] [RFC1195], to provide true layer 2 routing in specific
environments. This draft proposes a set of TLVs added to [IS-IS]
level 1 PDUs, and a new PDU type, to support these proposed systems.
This draft does not propose new forwarding mechanisms using this
additional information carried within IS-IS. There is a short
section included on two possible ways to build a shortest path first
tree including this information, to illustrate how this information
might be used.
2. Proposed Enhancements to IS-IS
This draft proposes a single TLV, the ADDR TLV, with two sub-TLVs,
for carrying a list of attaced addresses and pairs of related
addresses within IS-IS. This draft also proposes a new IS-IS PDU,
the Multicast Group (MGROUP) PDU, for carrying a list of attached or
joined multicast groups.
2.1. The ADDR TLV
The ADDR TLV is IS-IS TLV type [TBD], and has the following format:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Reserved |
+---------------+---------------+-------------------------------+
| Address Sub-TLVs....
+----
o Type: TLV Type, set to [TBD].
o Length: Total number of octets contained in the TLV, including the
length of each Sub-TLV within the ADDR TLV.
o Reserved: Set to 0.
The ADDR TLV MUST be carried in a level-1 psuedo-node LSP generated
by the originating IS.
An ADDR TLV may carry two types of sub-TLVs, addresses and
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attribtutes. This document defines two address sub-TLVs, and a
single attribute sub-TLV. All attribute sub-TLVs carried within a
single ADDR TLV apply to all of the address TLVs carried within the
same ADDR TLV.
If an ADDR TLV is carried within a standard Level 1 link state PDU,
it SHOULD contain only unicast addresses. If an ADDR TLV is carried
in an MGROUP PDU, described later in this document, it SHOULD contain
only multicast group addresses.
2.1.1. The Single AFI Type
A Single AFI TLV is used to carry a list of addresses of a single AFI
for devices attached to, or reachable from, the IS. One or more of
these sub-TLVs may be carried in the ADDR TLV.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | AFI Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| addresses |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ....
+----------------
o Type: Set to 1.
o Length: Set to the length of the sub-TLV in octets.
o AFI Type: The IANA defined AFI type of the included addresses
[IANA].
o Addresses: Addresses of the type and length indicated by the AFI
type.
2.1.2. The Address Pair Type
The Address Pair Sub-TLV carries a pair of related addresses, with
each address type defined using an IANA assigned AFI type. The first
address of the pair is the reachable through address, and the second
is the destination address. Zero or more Address Pair Type sub-TLVs
MAY be included in a single ADDR TLV.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | IS AFI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IS Address (variable length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AN AFI | AN Address (variable length) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ....
+-------------
o Type: Set to 2.
o Length: Set to the total number of octects in the sub-TLV.
o IS AFI: The IANA defined AFI type of address contained in the RT
Address [IANA].
o IS Address: The reachable through, or IS, address. The length of
this field is defined by the IANA defined AFI address type.
o AN AFI: The IANA defined AFI type of address contained in the AN
Address [IANA].
o AN Address: The attached node, or reachable, address. The length
of this field is defined by the IANA defined AFI address type.
This sub-TLV may be used in several ways, including (but not limited
to):
o The first address may be an IS address, with the second address
being an attached node.
o The first address may be an attached node layer 2 address, with
the second address being the same attached node's layer 3 address.
2.1.3. The VLAN Type
The VLAN sub-TLV carries a 32 bit VLAN identifier. All address sub-
TLVs carried within the same ADDR TLV as the VLAN sub-TLV are
considered part of the VLAN indicated in this sub-TLV.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Options |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| VLAN ID |
+---------------------------------------------------------------+
o Type: Set to 3.
o Length: Set to 4.
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o Options: Optional Flags
o VLAN ID: Set to the VLAN identifier.
The Options field is treated as 16 flags indicating additional
information about this VLAN or the status of the advertising IS on
this VLAN:
o Bit 0: If set, indicates this IS has directly connected end nodes
(or end nodes learned through some other mechanism than through
IS-IS).
o Bits 1-15: Reserved
2.2. The Multicast Group PDU
The Multicast Group (MGROUP) PDU can be used to advertise a set of
attached, or joined, multicast groups. The MGROUP PDU is formatted
identical to a Level 1 Link State PDU, as described in Section 9.3 of
[IS-IS]. One field, PDU Type, is changed to [TBD], to signify this
PDU is carrying multicast group information, rather than unicast
reachability information.
ADDR TLVs, described in the previous sections of this document, are
used to carry attached or joined multicast groups.
3. Considerations for Using L2 Information in IS-IS
While this document does not specify the way in which addresses
carried in these TLVs is used in IS-IS, two general areas of concern
are considered in this section: building the SPF tree when using this
information, and the election of designated intermediate systems
(DIS) in an environment using this information.
3.1. Building SPF Trees with Layer 2 Information
Each IS which is part of a single broadcast domain from a layer 2
perspective will build a single SPF tree (SPT) for every IS
indicating connected layer 2 end nodes or advertising direct
connections to layer 2 end nodes. An optimal unicast forwarding path
and an optimal flooding path to any given layer 2 address or set of
layer 2 addresses can be developed using these trees.
We assume some mechanism for forwarding traffic to these attached
addresses added to the SPT is provided for in the mechanism proposing
the use of these extension TLVs.
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3.2. Designated Intermediate Routers
A single DIS SHOULD be elected as described in [IS-IS] for each layer
2 broadcast domain (VLAN) for which information is being carried in
IS-IS. This reduces the amount of work required to flood and
maintain synchronized databases over the underlying media on which
IS-IS is running and providing layer 2 forwarding information for.
4. Acknowledgements
5. Security Considerations
This document adds no additional security risks to IS-IS, nor does it
provide any additional security for IS-IS.
6. IANA Considerations
This document creates a new TLV type within IS-IS, the ADDR TLV.
IANA SHOULD assign a TLV descriptor code (type) to this TLV.
This document creates a new sub-TLV numbering space for ADDR TLVs.
Within this space, this document defines three types. IANA SHOULD
manage the remaining space using the consensus method.
7. References
7.1. Normative References
[IS-IS] Heffernan, A., "Intermediate System to Intermediate System
Intra-Domain Routeing Exchange Protocol for use in
Conjunction with the Protocol for Providing the
Connectionless-mode Network Service (ISO 8473)", OSI
Standard ISO 10589, 1992.
7.2. Informative References
[RBRIDGES]
Perlman, R., Touch, J., and A. Yegin, "RBridges:
Transparent Routing", RFC
draft draft-perlman-rbridge-02.txt, February 2005.
[RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
dual environments", RFC 1195, December 1990.
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Authors' Addresses
David Ward
Cisco Systems
Email: wardd@cisco.com
Radia Perlman
Sun Microsystems
Email: Radia.Perlman@Sun.com
Russ White
Cisco Systems
Email: riw@cisco.com
Dino Farinacci
Cisco Systems
Email: dino@cisco.com
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