Networking Working Group                                 S. Previdi, Ed.
Internet-Draft                                               L. Ginsberg
Intended status: Standards Track                           Cisco Systems
Expires: April 20, 2013                                         M. Shand

                                                                  A. Roy
                                                                 D. Ward
                                                           Cisco Systems
                                                        October 17, 2012

                          IS-IS Multi-Instance


   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",
   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

   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."

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   This Internet-Draft will expire on April 20, 2013.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   publication of this document.  Please review these documents
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   described in the Simplified BSD License.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
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   Without obtaining an adequate license from the person(s) controlling
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   it for publication as an RFC or to translate it into languages other
   than English.

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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  . . . . . . . . . . . . . . . . . .  7
     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 . . . . . . . . . . . . . . . . .  8
       2.5.1.  Update Process Operation on Point-to-Point Circuits  .  8
       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 . . . . . . . . . . . . . . . . . . . . . . . 10
     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  . . . . . . . . . . . . . . . . 12
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 12
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 13
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 14
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14

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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"

   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.

   Another existing protocol limitation is that a given instance
   supports a single Update Process operating on a single Link State
   Database (LSDB).  This document defines an extension to IS-IS to
   allow non-zero instances of the protocol to support multiple Update
   Processes.  Each Update Process is associated with a topology and a
   unique topology specific LSDB.  Non-zero instances of the protocol
   are only supported by MI-RTRs.  Legacy routers support the standard
   or zero instance of the protocol.  The behavior of the standard
   instance is not changed in any way by the extensions defined in this

   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

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)

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   in each IS-IS PDU originated by an MI-RTR except as noted in this
   document.  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
   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 circuit
   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)) which are associated
   with a non-zero instance.

   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.  IS-IS PDUs associated with the standard
   instance MUST NOT include an IID-TLV except where noted in this

   The IID-TLV MAY include one or more ITIDs.  An ITID is a 16 bit
   identifier where all values (0 - 65535) are valid.

   The following format is used for the IID-TLV:

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     Type:   7
     Length: 2 - 254
                                            No. of octets
                 | IID (0 - 65535)         |     2
                 | Supported ITID          |     2
                 :                         :
                 | Supported ITID          |     2

     When the IID = 0, the list of supported ITIDs MUST NOT be present.

     An IID-TLV with IID = 0 MUST NOT appear in an SNP or LSP. When
     the TLV appears (with a non-zero IID) 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 or
     the IID is zero then 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 circuit over which the IIH is sent is
     included. There MUST BE at least one ITID present.

     Multiple IID-TLVs MAY appear in IIHs. If multiple IID-TLVs are
     present and the IID value in all IID-TLVs is not the same then
     the PDU MUST BE ignored.

   A single IID-TLV will support advertisement of up to 126 ITIDs.  If
   multiple IID-TLVs are present in an IIH PDU the supported set of
   ITIDs is the union of all ITIDs present in all IID-TLVs.

   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 without an IID-TLV belongs 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 non-zero instance in which it
   participates, an MI-RTR marks IS-IS PDUs (IIHs, LSPs or SNPs)
   generated pertaining to that instance by including the IID-TLV with
   the appropriate instance identifier.

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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.

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 circuit, 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 circuit.  However,
   as the instances are logically independent, the normal expectation of
   at most one neighbor on a given point-to-point circuit 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 circuit.  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.

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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.

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

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]) as the destination address when sending ISIS

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   PDUs for the standard instance (IID #0).  An MI-RTR will use two new
   (TBD) dedicated layer 2 multicast addresses (one for each level) as
   the destination address when sending IS-IS PDUs for any non-zero IID.
   If operating in point-to-point mode on a broadcast circuit [RFC5309]
   an MI-RTR MUST use one of the two new multicast addresses as the
   destination address when sending point-to-point IIHs associated with
   a non-zero instance.  (Either address will do.)

   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

   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 circuit as these PDUs may affect the state of IID #0 in the

   The presence/absence of the IID-TLV in an IIH indicates that the
   neighbor does/does not support this extension.  Therefore, all IIHs
   sent on a point-to-point circuit by an MI-RTR MUST include an IID-
   TLV.  This includes IIHs associated with IID #0.  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

   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.

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   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 one or more 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
   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-

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

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   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.

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

   If an MI-RTR uses the extensions in support of the BFD Enabled TLV
   [RFC6213] , the ITID SHOULD be used in place of the MTID in which
   case all 16 bits of the identifier field are useable.

   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.

   An MI-RTR MUST NOT support [RFC5120] multi-topology within a non-zero

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   instance.  The following TLVs MUST NOT be sent in an LSP associated
   with a non-zero instance and MUST be ignored when received:

    TLV 222 - MT IS Neighbors
    TLV 235 - MT IP Reachability
    TLV 237 - MT IPv6 Reachability

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.

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

   This document requires that two EUI-48 multicast addresses from the
   IANA managed EUI address space be allocated as specified in
   [RFC5342].  Requested block size is 2.

   The two addresses will be identified as AllL1MI-ISs and AllL2MI-ISs
   destination addresses.

7.  Security Considerations

   Security concerns for IS-IS are addressed in [IS-IS], [RFC5304], and

8.  Acknowledgements

   The authors would like to acknowledge contributions made by Dino
   Farinacci and Tony Li.

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9.  References

9.1.  Normative References

              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
              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.

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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.

   [RFC5342]  Eastlake, D., "IANA Considerations and IETF Protocol Usage
              for IEEE 802 Parameters", BCP 141, RFC 5342,
              September 2008.

Authors' Addresses

   Stefano Previdi (editor)
   Cisco Systems
   Via Del Serafico 200
   Rome  0144


   Les Ginsberg
   Cisco Systems
   510 McCarthy Blvd.
   Milpitas, CA  95035


   Mike Shand


   Abhay Roy
   Cisco Systems
   170 W. Tasman Dr.
   San Jose, CA  95134


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Internet-Draft          draft-ietf-isis-mi-08.txt           October 2012

   Dave Ward
   Cisco Systems
   3700 Cisco Way
   San Jose, CA  95134


Previdi, et al.          Expires April 20, 2013                [Page 15]