wdiff draft-previdi-isis-mi-mt-00.txt draft-previdi-isis-mi-mt-01.txt

INTERNET DRAFT IS-IS Multi-instance Multi-topology Jun 2006

Network Working Group S. Previdi
Internet Draft D. Ward L. Ginsberg
Expires: February,
Expiration Date: Dec 2006 M. Shand
A. Roy
D. Ward
Cisco Systems, Inc
August, 2005 Systems
June 2006

IS-IS Multi-instance Multi-topology
draft-previdi-isis-mi-mt-00.txt
draft-previdi-isis-mi-mt-01.txt

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Abstract

This draft describes a mechanism that allows a single router to
share one or more links among multiple IS-IS routing protocol
instances.

Multiple instances allow the deployment of multiple address-families
as well as multiple instances of the same address-family and it is
an alternative to Multi-Topology IS-IS. Routers supporting the same
instance will form instance
specific adjacencies, exchange instance specific routing updates and
compute
paths. paths utilizing instance specific LSDB information. Each PDU
will contain a new TLV identifying the instance to which the PDU
belongs. This allows a network operator to deploy multiple IS-IS
topologies in parallel, using the same set of links when required
and still have the capability of computing topology specific paths.
This draft does not address the forwarding paradigm that needs to be
used in order to ensure data PDUs are forwarded according to the
topology to which they belong.

Table of Contents

1. Conventions used in this document..............................2
2. Introduction...................................................2
3. Proposed Solution..............................................3
3.1 Instance Identifier..........................................3
3.2 Instance Membership..........................................3
3.3 Adjacency Establishment......................................4
3.3.1 Point-to-Point Adjacencies................................4
3.3.2 Multi-Access Adjacencies..................................4
3.4 Interoperability Considerations..............................4
3.4.1 MI-ISIS Layer 2 multicast address.........................5
3.4.2 Interoperability using p2p networks.......................5
3.4.3 Interoperability using Broadcast networks.................5
4. Security Considerations........................................6
5. IANA Considerations............................................6
6. Normative References...........................................6
7. Acknowledgments................................................6
8. Authors' Addresses.............................................7
9. Full Copyright Statement.......................................7

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 RFC-2119
[KEYWORDS]. [BCP14].

2. Introduction

IS-IS has been already extended in order

"[MT-IS-IS] defines extensions to IS-IS which support multiple
topologies [MT-ISIS] through the use of additional TLVs in IIH/LSP PDUs. MT-ISIS [MT-
IS-IS] specifies that a single adjacency, single flooding scheme,
and single LSDB are to be shared across all topologies to which a
router belongs. This draft describes an alternative approach where
multiple topologies are supported by the use of multiple independent
instances of the IS-IS protocol. Routers which support this
extension are referred to as "multi-instance capable routers"
(MI-RTR). (MI-
RTR).

3. Proposed Solution

The solution is based on a new TLV called the Instance Identifier
(IID) that is used to mark each routing IS-IS PDU originated by the router.
Routers form adjacencies and exchange routing updates only if their
IIDs correspond. Each topology is therefore processed within a
separate instance of the IS-IS protocol.

This also implies an instance specific flooding scheme, instance
specific LSDBs and Instance instance specific routing calculations. It MAY
also imply instance specific routing and forwarding tables. However,
this aspect is outside the scope of this specification. When
multiple instances share the same link each instance will have a
separate set of adjacencies. Each IS-IS PDU is associated with only
one IS-IS instance.

How multiple instances are implemented is outside the scope of this
specification.

3.1.

3.1 Instance Identifier (IID)

A new TLV is defined in order to convey an instance identifier
(IID). The scope purpose of the IID is to mark each IS-IS instance running
on a router with a unique 16-bit number. The IID TLV is carried in
all IS-IS PDUs (IIH, SNP, LSP) originated by the router. Routers
have to exchange Multiple
instances of IS-IS may co-exist on the same network and agree on instance numbers so that the same
physical router. IIDs can MUST be
understood consistently across adjacencies and flooding unique within the same routing domain.

Instance identifier #0 is reserved for the standard topology
supported by legacy systems.

The following format is used for the IID:

TLV:
Type: TBD
Length:

Type TBA by IANA
Length 2
Value:
Value <16-bit number IID>

3.2 Instance Membership

Each router can be is configured as part of to be participating in one or more
instances of IS-IS. Each For each instance the router belongs to will correspond to the
value advertised in the IID TLV of which it participates, a
router labels all IS-IS PDUs originated by (IIH, LSP or SNP) generated pertaining
to that
instance. Only one instance by including the appropriate IID TLV. Note that
this applies for the standard topology (instance identifier #0). A
PDU can only be advertised in an IIH, LSP, or SNP
PDU. labeled with a single instance identifier. PDUs with
multiple IID TLVs MUST be ignored.

3.3 Adjacency Establishment

In order to establish adjacencies, IS-IS routers exchange IIH PDUs.
Two types of adjacencies exist in IS-IS: point-to-point and
broadcast. The following sub-sections describe the additional rules
an MI-RTR MUST follow in order to establish when establishing adjacencies.

3.3.1 Point-to-Point Adjacencies

A new IID TLV is inserted into the p2p hello PDUs originated by an
MI-RTR. Upon reception of an IIH, an MI-RTR inspects the received
IID TLV and if it matches any of the IIDs configured on that link,
normal adjacency establishment procedures are used to establish an
instance specific adjacency.

This extension allows an MI-RTR to establish multiple adjacencies to
the same physical neighbor over a p2p link. This differs from the generic
normal behavior of on p2p links where only one adjacency is formed.
However, in this case IS-IS instances are "ships-in-the-night" and
from a logical perspective only one adjacency per instance is formed
on p2p links.

3.3.2 Multi-Access Adjacencies

Multi-Access (broadcast) networks behave differently than p2p in the
sense
that PDUs sent by one router are visible to all routers and all
routers must agree on the election of a DIS is elected. DIS.

MI-RTRs will establish adjacencies and elect a DIS per IS-IS
instance. Upon reception of an IIH each MI-RTR will form adjacencies
only with routers advertising the same IID in their IIH PDUs. Since
an MI-RTR is not required to participate in all IIDs on a LAN, it's
possible to elect a different DIS for different instances.

3.3.3

3.4 Interoperability Considerations

It is assumed that any TLV that is not understood is silently
ignored without compromising the processing of the whole IS-IS PDU
(IIH, LSP, SNP).

To a router not implementing this extension, all IS-IS PDUs received
will appear to be associated with the standard topology regardless
of any IID TLVs which may be contained in those PDUs. This can cause
interoperability issues, not all of which can be resolved. Therefore
deployment/configuration of MI-RTRs must be done prudently. MI-RTRs
may be configured issues unless the mechanisms and procedures
discussed below are followed.

3.4.1 MI-ISIS Layer 2 multicast address

In order for routers to accept or correctly interoperate with routers not
implementing this extension and in order not to form an adjacency cause disruption, a
specific and dedicated MAC address is used for multicasting IS-IS
PDUs labeled with any non-zero IID among MI-RTRs. Each level will
use a
router not supporting this extension. In specific layer 2 multicast address. Such an address allows MI-
RTRs to exchange IS-IS PDUs with non-zero IIDs without these PDUs
being processed by legacy routers and therefore no disruption is
caused.

An MI-RTR will exchange ISIS PDUs intended for IID #0 using AllL1IS
and AllL2IS ISIS mac layer addresses (as defined in [IS-IS]) and
will use two new (TBD) dedicated layer 2 multicast addresses (one
for each level) when sending IS-IS PDUs for any case, only non-zero IID.

MI-RTRs MUST discard IS-IS PDUs received if either of the following
is true:

. The destination multicast address is AllL1IS or AllL2IS and the
PDU contains an IID zero
instance can seamlessly interoperate TLV with routers not supporting
this extension.

3.3.3.1 non-zero value.

. The destination multicast address is one of the two new
addresses and the PDU contains an IID TLV with a zero value or
has no IID TLV.

3.4.2 Interoperability using p2p networks

MI-RTRs supporting IID #0 may

In order for an instance on an MI-RTR which participates in the
standard topology (IID #0) to interoperate over a p2p link with a
router which does NOT support this extension. To do so, an extension, the MI-RTR
must refrain from sending LSPs and SNPs MUST NOT
send IS-IS PDUs for instances other than IID #0 over the p2p link. It MUST also refrain from sending IIHs
for instance IDs other than zero link as
these IIHs PDUs may affect the state of the adjacency for IID #0 in the neighbor.

The presence/absence of the IID TLV in an IIH indicates that the
neighbor does/does not support this extension. Once it is determined
that the neighbor does not support this extension, an MI-RTR MUST
NOT send PDUs (including IIHs) for instances other than IID #0.

Until such time as the capability of the neighbor are known, an
implementation MAY send IIHs for any IID on a p2p link.

3.3.3.2

3.4.3 Interoperability using Multi-Access Broadcast networks

The presence on a multi-access network of one or more MI-RTRs
supporting one or more non-zero IIDs is incompatible with

If the
presence of any routers which do not support this extension. This is
because the necessary transmission of multicast addresses AllL1IS and/or AllL2IS are improperly
used to send IS-IS PDUs associated with for non-zero IIDs IIDs, legacy systems will be interpreted
interpret these PDUs as being associated with IID #0 by #0. This will
cause inconsistencies in the routers not supporting this extension. Therefore, use of this
extension on a multi-access network requires that all routers LSDB in those routers, may incorrectly
maintain adjacencies, and may lead to inconsistent DIS election.

4. Security Considerations

Security concerns for IS-IS are
upgraded addressed in the IS-IS specification
[IS-IS], and accompanying specifications on [HMAC-MD5]. No
additional considerations need to a software version supporting this extension. This
restriction MAY be applied independently made for each level of routing
supported on the network.

4. IANA considerations extension.

5. IANA will assign Considerations

This document requires the definition a new codepoint for the MI-MT IID defined ISIS TLV that needs to
be reflected in this
document and carried within the ISIS TLV code-point registry:

Type Description IIH PDU. Suggest value is XX (to be
assigned by IANA).

5. Acknowledgments

The authors would like to thank Mike Shand for his valuable input. LSP SNP
---- ----------------------------------- --- --- ---
TBA MI-MT IID y y y

6. Normative References

[RFC] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels," RFC 2119.

[IS-IS] ISO, "Intermediate System system to Intermediate System Intra-Domain
Routeing Exchange Protocol system routeing
information exchange protocol for use in Conjunction conjunction with the
Protocol for Providing providing the Connectionless-mode Network Service
(ISO 8473)",
ISO 10589.

[IS-IS-IP] Callon, R., RFC 1195, "Use of OSI IS-IS for routing in
TCP/IP 8473)," ISO/IEC 10589:2002, Second Edition.

[MT-IS-IS] Pryzgienda, T., Shen, N., and dual environments", RFC 1195, December 1990. Sheth, N., "Multi
Topology (MT) Routing in IS-IS", draft-ietf-isis-wg-multi-
topology-11.txt (work in progress), October 2005.

[HMAC-MD5] Li, T. and R. Atkinson, "Intermediate System to
Intermediate System (IS-IS) Cryptographic Authentication", RFC
3567, July 2003.

[MT-IS-IS] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
Topology (MT) Routing in IS-IS", draft-ietf-isis-wg-multi-topology-
10.txt, May 2005.

7. Security Considerations

Security concerns

[BCP9] Bradner, S., "The Internet Standards Process -- Revision
3", BCP 9, RFC 2026, October 1996.

[BCP14] Bradner, S., "Key words for IS-IS are addressed use in the IS-IS specification
[IS-IS], RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997

[BCP26] Narten, T. and accompanying specifications on [HMAC-MD5]. No
additional considerations need Alvestrand, H., "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26 , RFC 2434, October
1998

[BCP79] Bradner, S. Ed., "Intellectual Property Rights in IETF
Technology ", BCP 79 , RFC 3979, March 2005

7. Acknowledgments

The authors would like to be acknowledge contributions made for the extension. by Dino
Farinacci.

8. Authors' Addresses

Stefano Previdi
Cisco Systems
CISCO Systems, Inc.
Via Del Serafico, Serafico 200
00142 Rome, Italy - Roma
ITALY
Email: sprevidi@cisco.com

Dave Ward

Les Ginsberg
Cisco Systems
170 W. Tasman Dr.
San Jose, CA 95134
510 McCarthy Blvd.
Milpitas, Ca. 95035 USA
dward@cisco.com

Les Ginsberg
Email: ginsberg@cisco.com

Abhay Roy
Cisco Systems
170 W. Tasman Dr.
San Jose, CA 95134 USA
ginsberg@cisco.com

Abhay Roy
akr@cisco.com

Mike Shand
Cisco Systems
250 Longwater Avenue,
Reading,
Berkshire,
RG2 6GB
UK
Email: mshand@cisco.com

Dave Ward
Cisco Systems
170 W. Tasman Dr.
San Jose, CA 95134 USA
akr@cisco.com
dward@cisco.com

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