Networking Working Group S. Previdi, Ed.
Internet-Draft L. Ginsberg
Intended status: Standards Track Cisco Systems
Expires: May 2, 2012 M. Shand
A. Roy
Cisco Systems
D. Ward
Juniper Networks
October 30, 2011
IS-IS Multi-Instance
draft-ietf-isis-mi-05.txt
Abstract
This draft describes a mechanism that allows a single router to share
one or more circuits among multiple Intermediate System To
Intermediate System (IS-IS) routing protocol instances.
Multiple instances allow the isolation of resources associated with
each instance. Routers will form instance specific adjacencies.
Each instance can support multiple topologies. Each topology has a
unique Link State Database (LSDB). Each Protocol Data Unit (PDU)
will contain a new Type Length Value (TLV) identifying the instance
and the topology(ies) to which the PDU belongs.
Requirements Language
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 [RFC2119].
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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
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."
Previdi, et al. Expires May 2, 2012 [Page 1]
Internet-Draft draft-ietf-isis-mi-05.txt October 2011
This Internet-Draft will expire on May 2, 2012.
Copyright Notice
Copyright (c) 2011 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.
This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
10, 2008. The person(s) controlling the copyright in some of this
material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
Previdi, et al. Expires May 2, 2012 [Page 2]
Internet-Draft draft-ietf-isis-mi-05.txt October 2011
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Elements Of Procedure . . . . . . . . . . . . . . . . . . . . 4
2.1. Instance Identifier TLV . . . . . . . . . . . . . . . . . 5
2.2. Instance Membership . . . . . . . . . . . . . . . . . . . 6
2.3. Use of Authentication . . . . . . . . . . . . . . . . . . 6
2.4. Adjacency Establishment . . . . . . . . . . . . . . . . . 7
2.4.1. Point-to-Point Adjacencies . . . . . . . . . . . . . . 7
2.4.2. Multi-Access Adjacencies . . . . . . . . . . . . . . . 7
2.5. Update Process Operation . . . . . . . . . . . . . . . . . 7
2.5.1. Update Process Operation on Point-to-Point Circuits . 7
2.5.2. Update Process Operation on Broadcast Circuits . . . . 8
2.6. Interoperability Considerations . . . . . . . . . . . . . 8
2.6.1. Interoperability Issues on Broadcast Circuits . . . . 8
2.6.2. Interoperability using point-to-point circuits . . . . 9
3. Usage Guidelines . . . . . . . . . . . . . . . . . . . . . . . 9
3.1. One-One Mapping Between Topologies and Instances . . . . . 10
3.2. Many-to-one Mapping Between Topologies and Instances . . . 10
3.3. Considerations for the Number of Instances . . . . . . . . 11
4. Relationship to M-ISIS . . . . . . . . . . . . . . . . . . . . 11
5. Graceful Restart Interactions . . . . . . . . . . . . . . . . 11
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
7. Security Considerations . . . . . . . . . . . . . . . . . . . 12
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
9.1. Normative References . . . . . . . . . . . . . . . . . . . 12
9.2. Informative References . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
Previdi, et al. Expires May 2, 2012 [Page 3]
Internet-Draft draft-ietf-isis-mi-05.txt October 2011
1. Introduction
An existing limitation of the protocol defined by [IS-IS] is that
only one instance of the protocol can operate on a given circuit.
This document defines an extension to IS-IS to remove this
restriction. The extension is referred to as "Multi-instance IS-IS"
(MI-IS-IS).
Routers which support this extension are referred to as "Multi-
instance capable routers" (MI-RTR).
The use of multiple instances enhances the ability to isolate the
resources associated with a given instance both within a router and
across the network. Instance specific prioritization for processing
PDUs and performing routing calculations within a router may be
specified. Instance specific flooding parameters may also be defined
so as to allow different instances to consume network wide resources
at different rates.
A given instance MAY support multiple topologies. Each topology is
associated with a unique LSDB and a topology specific IS-IS Update
Process. This differs from [RFC5120] where a single LSDB/single
IS-IS Update Process is used in support of all topologies.
MI-IS-IS might be used to support topology specific routing. When
used for this purpose it is an alternative to [RFC5120].
MI-IS-IS might also be used to support advertisement of information
on behalf of applications [I-D.ietf-isis-genapp]. The advertisement
of information not directly related to the operation of the IS-IS
protocol can therefore be done in a manner which minimizes its impact
on the operation of routing.
The above are examples of how MI-IS-IS might be used. The
specification of uses of MI-IS-IS is outside the scope of this
document.
2. Elements Of Procedure
An Instance Identifier (IID) is introduced to uniquely identify an
IS-IS instance. The protocol extension includes a new TLV (IID-TLV)
in each IS-IS PDU originated by an MI-RTR. The IID-TLV identifies
the unique instance as well as the topology/topologies to which the
PDU applies. Each IS-IS PDU is associated with only one IS-IS
instance.
MI-RTRs form instance specific adjacencies. The IID-TLV included in
Previdi, et al. Expires May 2, 2012 [Page 4]
Internet-Draft draft-ietf-isis-mi-05.txt October 2011
Intermediate System-Intermediate System Hellos (IIH) includes the IID
and the set of Instance Specific Topology Identifiers (ITID) that the
sending IS supports. When multiple instances share the same link
each instance will have a separate set of adjacencies.
MI-RTRs support the exchange of topology specific Link State PDUs for
the IID/ITID pairs that each neighbor supports. A unique IS-IS
Update process [see IS-IS] operates for each IID/ITID pair. This MAY
also imply IID/ITID specific routing calculations and IID/ITID
specific routing and forwarding tables. However, this aspect is
outside the scope of this specification.
The mechanisms used to implement support of the separation of IS-IS
instances and topology specific Update processes within a router are
outside the scope of this specification.
2.1. Instance Identifier TLV
A new TLV is defined in order to convey the IID and ITIDs supported.
The IID-TLV associates PDUs with each IS-IS instance using a unique
16-bit number. The IID-TLV is carried in all IS-IS PDUs
(Intermediate System to Intermediate System Hellos (IIH), Sequence
Number PDUs (SNP) and Link State PDUs (LSP)) originated by the
router.
Multiple instances of IS-IS may co-exist on the same circuit and on
the same physical router. IIDs MUST be unique within the same
routing domain.
Instance identifier #0 is reserved for the standard instance
supported by legacy systems. The following format is used for the
IID-TLV:
Previdi, et al. Expires May 2, 2012 [Page 5]
Internet-Draft draft-ietf-isis-mi-05.txt October 2011
Type: 7
Length: 2 - 255
Value:
No. of octets
+-------------------------+
| IID (0 - 65535) | 2
+-------------------------+
| Supported ITID (0 - 255)| 0 - 253
+-------------------------+
When the IID = 0, the list of supported ITIDs MUST NOT be present.
When the IID is non-zero and the TLV appears in an SNP or LSP,
exactly one ITID MUST be present indicating the topology with
which the PDU is associated. If no ITIDs or multiple ITIDs are
present the PDU MUST be ignored.
When the IID is non-zero and the TLV appears in an IIH, the set
of ITIDs supported on the link over which the IIH is sent is
included. There MUST BE at least one ITID present.
When an LSP purge is initiated, the IID-TLV MUST be retained but the
remainder of the body of the LSP SHOULD be removed. Purge procedure
is described in [RFC6233] and [RFC6232].
A PDU MUST NOT be generated with multiple IID-TLVs. PDUs received
with multiple IID-TLVs MUST be ignored. A PDU without an IID-TLV is
assumed to belong to the standard instance (#0).
2.2. Instance Membership
Each MI-RTR is configured to be participating in one or more
instances of IS-IS. For each instance in which it participates, an
MI-RTR marks all IS-IS PDUs (IIHs, LSPs or SNPs) generated pertaining
to that instance by including the IID-TLV with the appropriate
instance identifier.
2.3. Use of Authentication
When authentication is in use, the IID, if present, is first used to
select the authentication configuration which is applicable. The
authentication check is then performed as normal. When multiple
ITIDs are supported, ITID specific authentication MAY be used in SNPs
and LSPs.
Previdi, et al. Expires May 2, 2012 [Page 6]
Internet-Draft draft-ietf-isis-mi-05.txt October 2011
2.4. 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 when establishing adjacencies.
2.4.1. Point-to-Point Adjacencies
MI-RTRs include the IID-TLV in the point-to-point hello PDUs they
originate. Upon reception of an IIH, an MI-RTR inspects the received
IID-TLV and if the IID matches any of the IIDs which the router
supports on that link, normal adjacency establishment procedures are
used to establish an instance specific adjacency. Note that the
absence of the IID TLV implies instance ID #0. For instances other
than IID #0, an adjacency SHOULD NOT be established unless there is
at least one ITID in common.
This extension allows an MI-RTR to establish multiple adjacencies to
the same physical neighbor over a point-to-point link. However, as
the instances are logically independent, the normal expectation of at
most one neighbor on a given point-to-point link still applies.
2.4.2. Multi-Access Adjacencies
Multi-Access (broadcast) circuits behave differently than point-to-
point in that PDUs sent by one router are visible to all routers and
all routers must agree on the election of a Designated Intermediate
System (DIS) independent of the set of ITIDs supported.
MI-RTRs will establish adjacencies and elect a DIS per IS-IS
instance. Each MI-RTR will form adjacencies only with routers which
advertise support for the instances which the local router has been
configured to support on that link. Since an MI-RTR is not required
to support all possible instances on a LAN, it's possible to elect a
different DIS for different instances.
2.5. Update Process Operation
For non-zero instances, a unique Update Process exists for each
supported ITID.
2.5.1. Update Process Operation on Point-to-Point Circuits
On Point-to-Point circuits - including Point-to-Point Operation over
LAN [RFC5309] - the ITID specific Update Process only operates on
that circuit for those ITIDs which are supported by both ISs
operating on the circuit.
Previdi, et al. Expires May 2, 2012 [Page 7]
Internet-Draft draft-ietf-isis-mi-05.txt October 2011
2.5.2. Update Process Operation on Broadcast Circuits
On Broadcast circuits, a single DIS is elected for each supported IID
independent of the set of ITIDs advertised in LAN IIHs. This
requires that the DIS generate pseudo-node LSPs for all supported
ITIDs and that the Update Process for all supported ITIDs operate on
the Broadcast Circuit. In cases where the set of supported ITIDs for
a given non-zero IID is inconsistent among the MI-RTRs operating on a
broadcast circuit, connectivity for the topology(ies) associated with
ITIDs not supported by some MI-RTRs operating on the circuit can be
compromised.
2.6. Interoperability Considerations
[IS-IS] requires 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 instance regardless of
whether an IID TLV is present in those PDUs. This can cause
interoperability issues unless the mechanisms and procedures
discussed below are followed.
2.6.1. Interoperability Issues on Broadcast Circuits
In order for routers to correctly interoperate with routers not
implementing this extension and in order not to cause disruption, a
specific and dedicated Media Access Control (MAC) address is used for
multicasting IS-IS PDUs with any non-zero IID. Each level will use a
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 use the AllL1IS and AllL2IS ISIS MAC layer addresses
(as defined in [IS-IS]) when sending ISIS PDUs for the standard
instance (IID #0). An MI-RTR will use two new (TBD) dedicated layer
2 multicast addresses (one for each level) when sending IS-IS PDUs
for any non-zero IID.
MI-RTRs MUST discard IS-IS PDUs received if either of the following
is true:
o The destination multicast address is AllL1IS or AllL2IS and the
PDU contains an IID-TLV
Previdi, et al. Expires May 2, 2012 [Page 8]
Internet-Draft draft-ietf-isis-mi-05.txt October 2011
o The destination multicast address is one of the two new addresses
and the PDU contains an IID-TLV with a zero value for the IID or
has no IID-TLV.
NOTE: If the multicast addresses AllL1IS and/or AllL2IS are
improperly used to send IS-IS PDUs for non-zero IIDs, legacy systems
will interpret these PDUs as being associated with IID #0. This will
cause inconsistencies in the LSDB in those routers, may incorrectly
maintain adjacencies, and may lead to inconsistent DIS election.
2.6.2. Interoperability using point-to-point circuits
In order for an MI-RTR to interoperate over a point-to-point circuit
with a router which does NOT support this extension, the MI-RTR MUST
NOT send IS-IS PDUs for instances other than IID #0 over the point-
to-point link as these PDUs may affect the state of 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 an IIH is received from a neighbor, an MI-RTR MAY send IIHs for
a non-zero instance. However, once an IIH with no IID TLV has been
received - indicating that the neighbor is not an MI-RTR - the MI-RTR
MUST NOT send IIHs for a non-zero instance. The temporary relaxation
of the restriction on sending IIHs for non-zero instances allows a
non-zero instance adjacency to be established on an interface on
which an MI-RTR does NOT support instance #0.
Point-to-point adjacency setup MUST be done through the use of three-
way handshaking procedure as defined in [RFC5303] in order to prevent
a non-MI capable neighbor from bringing up an adjacency prematurely
based on reception of an IIH w an IID-TLV for a non-zero instance.
3. Usage Guidelines
As discussed above, MI-IS-IS extends IS-IS to support multiple
instances on a given circuit. Each instance is uniquely identified
by the IID and forms instance specific adjacencies. Each instance
supports 1-255 topologies as represented by the ITIDs. All
topologies associated with a given instance share the instance
specific adjacencies. The set of topologies supported by a given IID
MAY differ from circuit to circuit. Each topology has its own set of
LSPs and runs a topology specific Update process. Flooding of
topology specific LSPs is only performed on circuits on which both
Previdi, et al. Expires May 2, 2012 [Page 9]
Internet-Draft draft-ietf-isis-mi-05.txt October 2011
the local router and the neighbor(s) support a given topology (i.e.
advertise the same ITID in the set of supported ITIDs sent in the
IID-TLV included in IIHs).
The following sub-sections provide some guidelines for usage of
instances and topologies within each instance. While this represents
examples based on the intent of the authors, implementors are not
constrained by the examples.
3.1. One-One Mapping Between Topologies and Instances
When the set of information to be flooded in LSPs is intended to be
flooded to all MI-RTRs supporting a given IID a single topology MAY
be used. The information contained in the single LSDB MAY still
contain information associated with multiple applications as the
GENINFO TLV for each application has an application specific ID which
identifies the application to which the TLV applies [I-D.ietf-isis-
genapp].
3.2. Many-to-one Mapping Between Topologies and Instances
When the set of information to be flooded in LSPs includes subsets
which are of interest to a subset of the MI-RTRs supporting a given
IID, support of multiple ITIDs allows each subset to be flooded only
to those MI-RTRs which are interested in that subset. In the
simplest case, a one-one mapping between a given application and an
ITID allows the information associated with that application to be
flooded only to MI-RTRs which support that application - but a many-
to-one mapping between applications and a given ITID is also
possible. When the set of application specific information is large,
the use of multiple ITIDs provides significantly greater efficiencies
as MI-RTRs only need to maintain the LSDB for applications of
interest and that information only needs to be flooded over a
topology defined by the MI-RTRs who support a given ITID.
The use of multiple ITIDs also allows the dedication of a full LSP
set (256 LSPs at each level) for the use of a given (set of)
applications, thereby minimizing the possibility of exceeding the
carrying capacity of an LSP set which might arise if information for
all applications were to be included in a single LSP set.
Note that the topology associated with each ITID MUST be fully
connected in order for ITID specific LSPs to be successfully flooded
to all MI-RTRs who support that ITID.
Previdi, et al. Expires May 2, 2012 [Page 10]
Internet-Draft draft-ietf-isis-mi-05.txt October 2011
3.3. Considerations for the Number of Instances
The support of multiple topologies within the context of a single
instance provides better scalability in support of multiple
applications both in terms of the number of adjacencies which are
required and in the flooding of topology specific LSDB. In many
cases the use of a single non-zero instance would be sufficient and
optimal. However, in cases where the set of topologies desired in
support of a set of applications is largely disjoint from the set of
topologies desired in support of a second set of applications, it
could make sense to use multiple instances.
4. Relationship to M-ISIS
[RFC5120] defines support for Multi-Topology Routing. In that
document 12 bit Multi-topology IDs are defined to identify the
topologies which an IS-IS instance (a "standard instance" as defined
by this document) supports. There is no relationship between the
Multi-topology IDs defined in [RFC5120] and the ITIDs defined in this
document.
If an MI-RTR uses the extensions in support of the BFD Enabled TLV
[RFC6213] , the 8 bit ITID (0 filled) SHOULD be used in place of the
MTID.
An MI-RTR MAY use the extensions defined in this document to support
multiple topologies in the context of an instance with a non-zero
IID. Each MI topology is associated with a unique LSDB identified by
an ITID. An ITID specific IS-IS Update Process operates on each
topology. This differs from [RFC5120] where a single LSDB/single
IS-IS Update Process is used in support of all topologies. Although
it is possible for an MI-RTR to use [RFC5120] multi-topology support
within a non-zero instance such usage is seen as unnecessary and is
discouraged.
5. Graceful Restart Interactions
[RFC5306] defines protocol extensions in support of graceful restart
of a routing instance. The extensions defined there apply to MI-RTRs
with the notable addition that as there are topology specific LSP
databases each of these must be synchronized following restart in
order for database synchronization to be complete. This involves the
use of additional T2 timers. See [RFC5306] for further details.
Previdi, et al. Expires May 2, 2012 [Page 11]
Internet-Draft draft-ietf-isis-mi-05.txt October 2011
6. IANA Considerations
This document requires the definition of a new ISIS TLV that needs to
be reflected in the ISIS TLV code-point registry:
Type Description IIH LSP SNP Purge
---- --------------------- --- --- --- -----
7 Instance Identifier y y y y
7. Security Considerations
Security concerns for IS-IS are addressed in [IS-IS], [RFC5304], and
[RFC5310].
Use of the extensions defined here with authentication as defined in
[RFC5304] or [RFC5310] will result in the discarding of purges by
legacy systems which are in strict conformance with either of those
RFCs. To avoid this issue an MI-RTR MAY omit the IID-TLV in purges
for the standard instance (IID #0) until such time as all ISs in the
network have been upgraded to support [RFC6232].
8. Acknowledgements
The authors would like to acknowledge contributions made by Dino
Farinacci and Tony Li.
9. References
9.1. Normative References
[I-D.ietf-isis-genapp]
Ginsberg, L., Previdi, S., and M. Shand, "Advertising
Generic Information in IS-IS", draft-ietf-isis-genapp-04
(work in progress), November 2010.
[IS-IS] "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.
[RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
Previdi, et al. Expires May 2, 2012 [Page 12]
Internet-Draft draft-ietf-isis-mi-05.txt October 2011
Topology (MT) Routing in Intermediate System to
Intermediate Systems (IS-ISs)", RFC 5120, February 2008.
[RFC5303] Katz, D., Saluja, R., and D. Eastlake, "Three-Way
Handshake for IS-IS Point-to-Point Adjacencies", RFC 5303,
October 2008.
[RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic
Authentication", RFC 5304, October 2008.
[RFC5306] Shand, M. and L. Ginsberg, "Restart Signaling for IS-IS",
RFC 5306, 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.
[RFC6213] Hopps, C. and L. Ginsberg, "IS-IS BFD-Enabled TLV",
RFC 6213, April 2011.
[RFC6232] Wei, F., Qin, Y., Li, Z., Li, T., and J. Dong, "Purge
Originator Identification TLV for IS-IS", RFC 6232,
May 2011.
[RFC6233] Li, T. and L. Ginsberg, "IS-IS Registry Extension for
Purges", RFC 6233, May 2011.
9.2. Informative References
[RFC5309] Shen, N. and A. Zinin, "Point-to-Point Operation over LAN
in Link State Routing Protocols", RFC 5309, October 2008.
Authors' Addresses
Stefano Previdi (editor)
Cisco Systems
Via Del Serafico 200
Rome 0144
Italy
Email: sprevidi@cisco.com
Previdi, et al. Expires May 2, 2012 [Page 13]
Internet-Draft draft-ietf-isis-mi-05.txt October 2011
Les Ginsberg
Cisco Systems
510 McCarthy Blvd.
Milpitas, CA 95035
USA
Email: ginsberg@cisco.com
Mike Shand
Email: imc.shand@googlemail.com
Abhay Roy
Cisco Systems
170 W. Tasman Dr.
San Jose, CA 95134
USA
Email: akr@cisco.com
Dave Ward
Juniper Networks
1194 N. Mathilda Ave.
Sunnyvale, CA 94089-1206
USA
Email: dward@juniper.net
Previdi, et al. Expires May 2, 2012 [Page 14]