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rfc:rfc8202

Internet Engineering Task Force (IETF) L. Ginsberg Request for Comments: 8202 S. Previdi Obsoletes: 6822 Cisco Systems Category: Standards Track W. Henderickx ISSN: 2070-1721 Nokia

                                                             June 2017
                        IS-IS Multi-Instance

Abstract

 This document 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 (or topologies) to which the PDU belongs.
 This document obsoletes RFC 6822.

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 7841.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc8202.

Ginsberg, et al. Standards Track [Page 1] RFC 8202 IS-IS Multi-Instance June 2017

Copyright Notice

 Copyright (c) 2017 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.

Table of Contents

 1. Introduction ....................................................3
 2. Requirements Language ...........................................4
 3. Elements of Procedure ...........................................4
    3.1. Instance Identifier TLV ....................................4
    3.2. Instance Membership ........................................6
    3.3. Use of Authentication ......................................6
    3.4. Adjacency Establishment ....................................6
         3.4.1. Point-to-Point Adjacencies ..........................6
         3.4.2. Multi-Access Adjacencies ............................7
    3.5. Update Process Operation ...................................7
         3.5.1. Update Process Operation on Point-to-Point
                Circuits ............................................7
         3.5.2. Update Process Operation on Broadcast Circuits ......7
    3.6. Interoperability Considerations ............................7
         3.6.1. Interoperability Issues on Broadcast Circuits .......8
         3.6.2. Interoperability Using Point-to-Point Circuits ......9
 4. Usage Guidelines ................................................9
    4.1. One-to-One Mapping between Topologies and Instances .......10
    4.2. Many-to-One Mapping between Topologies and Instances ......10
    4.3. Considerations for the Number of Instances ................11
 5. Relationship to M-ISIS .........................................11
 6. Graceful Restart Interactions ..................................12
 7. IANA Considerations ............................................12
 8. Security Considerations ........................................12
 9. References .....................................................12
    9.1. Normative References ......................................12
    9.2. Informative References ....................................14
 Appendix A. Changes to RFC 6822 ...................................15
 Acknowledgements ..................................................15
 Authors' Addresses ................................................16

Ginsberg, et al. Standards Track [Page 2] RFC 8202 IS-IS Multi-Instance June 2017

1. Introduction

 An existing limitation of the protocol defined by [ISO10589] 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 that 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
 document.
 MI-IS-IS might be used to support topology-specific routing.  Two
 methods of supporting such a use are defined in this document: one
 supports the use of [RFC5120] within a reserved instance-specific
 topology and the other is an alternative to [RFC5120] that supports
 topology-specific flooding of link state information.
 MI-IS-IS might also be used to support the advertisement of
 information on behalf of applications [RFC6823].  The advertisement
 of information not directly related to the operation of the IS-IS
 protocol can therefore be done in a manner that 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.

Ginsberg, et al. Standards Track [Page 3] RFC 8202 IS-IS Multi-Instance June 2017

2. Requirements Language

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
 "OPTIONAL" in this document are to be interpreted as described in
 BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
 capitals, as shown here.

3. 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 except as noted in this
 document.  The IID-TLV identifies the unique instance as well as the
 instance-specific 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
 IS-IS Hellos (IIHs) includes the IID and the set of Instance-specific
 Topology Identifiers (ITIDs) 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 [ISO10589]) 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.

3.1. Instance Identifier TLV

 A new TLV is defined in order to convey the IID and ITIDs supported.
 The IID-TLV associates a PDU with an IS-IS instance using a unique
 16-bit number.  The IID-TLV is carried in all IS-IS PDUs that are
 associated with a non-zero instance; this includes IIHs, Sequence
 Number PDUs (SNPs), and Link State PDUs (LSPs) .
 Multiple instances of IS-IS may coexist on the same circuit and on
 the same physical router.  IIDs MUST be unique within the same
 routing domain.

Ginsberg, et al. Standards Track [Page 4] RFC 8202 IS-IS Multi-Instance June 2017

 IID #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 document.
 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:
   Type:   7
   Length: 2 - 254
   Value:
                                          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 instance-specific
    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.
    ITID #0 is reserved for a specific use case as described later in
    this document.  ITID #0 MUST NOT be supported in combination with
    any non-zero ITID.  If multiple ITIDs are advertised in an IIH and
    one of the ITIDs is #0, then the PDU MUST be ignored.
    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.

Ginsberg, et al. Standards Track [Page 5] RFC 8202 IS-IS Multi-Instance June 2017

 When an LSP purge is initiated, the IID-TLV MUST be retained, but the
 remainder of the body of the LSP SHOULD be removed.  The purge
 procedure is described in [RFC6233] and [RFC6232].
 It is recommended that (when present) the IID-TLV(s) be the first
 TLV(s) in the PDU.  This allows determination of the association of a
 PDU with a particular instance more quickly.
 A PDU without an IID-TLV belongs to the standard instance.

3.2. 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 that pertain to that instance by including the IID-TLV with
 the appropriate instance identifier.

3.3. Use of Authentication

 When authentication is in use, the IID, if present, is first used to
 select the authentication configuration that 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.

3.4. 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 subsections describe the additional rules
 an MI-RTR MUST follow when establishing adjacencies for non-zero
 instances.

3.4.1. Point-to-Point Adjacencies

 MI-RTRs include the IID-TLV in the point-to-point Hello PDUs
 associated with non-zero instances that they originate.  Upon
 reception of an IIH, an MI-RTR inspects the received IID-TLV, and if
 the IID matches any of the IIDs that 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 IID #0.  For instances other than IID #0, an
 adjacency SHOULD NOT be established unless there is at least one ITID
 in common.

Ginsberg, et al. Standards Track [Page 6] RFC 8202 IS-IS Multi-Instance June 2017

 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.

3.4.2. 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 that
 advertise support for the instances that 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.

3.5. Update Process Operation

 For non-zero instances, a unique Update Process exists for each
 supported ITID.

3.5.1. 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 that are supported by both ISs operating
 on the circuit.

3.5.2. 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.  Among MI-RTRs operating on a broadcast
 circuit, if the set of supported ITIDs for a given non-zero IID is
 inconsistent, connectivity for the topology (or topologies)
 associated with the ITIDs not supported by some MI-RTRs can be
 compromised.

3.6. Interoperability Considerations

 [ISO10589] requires that any TLV that is not understood be silently
 ignored without compromising the processing of the whole IS-IS PDU
 (IIH, LSP, SNP).

Ginsberg, et al. Standards Track [Page 7] RFC 8202 IS-IS Multi-Instance June 2017

 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.

3.6.1. 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; therefore, no disruption is caused.
 When sending SNPs, LSPs, and LAN IIHs for the standard instance (IID
 #0), an MI-RTR will use either the AllL1IS or the AllL2IS MAC-layer
 addresses (as defined in [ISO10589]) as the destination address.
 When sending SNPs, LSPs, and LAN IIHs for any non-zero IID, an MI-RTR
 MUST use one of two new dedicated Layer 2 multicast addresses
 (AllL1MI-ISs or AllL2MI-ISs) as the destination address.  These
 addresses are specified in Section 7.
 MI-RTRs MUST discard IS-IS PDUs received if either of the following
 is true:
 o  The destination multicast address is AllL1IS, AllL2IS, or AllIS
    and the PDU contains an IID-TLV.
 o  The destination multicast address is AllL1MI-ISs or AllL2MI-ISs
    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, AllL2IS, and/or AllIS 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.

3.6.1.1. Special Considerations when Operating in Point-to-Point Mode

 When operating in point-to-point mode on a broadcast circuit
 [RFC5309], an MI-RTR will use AllL1IS, AllL2IS, or AllIS MAC-layer
 addresses when sending SNPs, LSPs, and point-to-point IIHs associated
 with the standard instance.  When sending SNPs, LSPs, and point-to-
 point IIHs for a non-zero IID, an MI-RTR MUST use one of the two new

Ginsberg, et al. Standards Track [Page 8] RFC 8202 IS-IS Multi-Instance June 2017

 multicast addresses (AllL1MI-ISs or AllL2MI-IS) as the destination
 address.  When sending point-to-point IIHs for a non-zero IID, either
 address is permitted.

3.6.2. Interoperability Using Point-to-Point Circuits

 In order for an MI-RTR to interoperate over a point-to-point circuit
 with a router that 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
 neighbor.
 The presence or absence of the IID-TLV in an IIH indicates that the
 neighbor does or does not support this extension, respectively.
 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 #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 the standard instance.
 Point-to-point adjacency setup MUST be done through the use of the
 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 with an IID-TLV for a
 non-zero instance.

4. 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).

Ginsberg, et al. Standards Track [Page 9] RFC 8202 IS-IS Multi-Instance June 2017

 The following subsections 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.

4.1. One-to-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 that
 identifies the application to which the TLV applies [RFC6823].

4.2. Many-to-One Mapping between Topologies and Instances

 When the set of information to be flooded in LSPs includes subsets
 that 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 that are interested in that subset.  In the simplest
 case, a one-to-one mapping between a given application and an ITID
 allows the information associated with that application to be flooded
 only to MI-RTRs that 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.  Such a possibility 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 that support that ITID.
 When multiple ITIDs are supported by an instance, ITID #0 MUST NOT be
 supported.

Ginsberg, et al. Standards Track [Page 10] RFC 8202 IS-IS Multi-Instance June 2017

4.3. 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 that 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.

5. Relationship to M-ISIS

 [RFC5120] defines support for multi-topology routing.  In that
 document, 12-bit Multi-Topology Identifiers (MTIDs) are defined to
 identify the topologies that an IS-IS instance (a "standard instance"
 as defined by this document) supports.  There is no relationship
 between the MTIDs defined in [RFC5120] and the ITIDs defined in this
 document.
 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 and
 single IS-IS Update Process are used in support of all topologies.
 In such cases, if an MI-RTR uses the extensions in support of the
 BFD-Enabled TLV [RFC6213], the ITID MUST be used in place of the
 MTID; in which case, all 16 bits of the identifier field are useable.
 An MI-RTR MAY support [RFC5120] multi-topology within a non-zero
 instance when ITID #0 is supported.  When ITID #0 is supported it
 MUST be the only ITID supported by that instance.  In such cases, if
 an MI-RTR uses the extensions in support of the BFD Enabled TLV
 [RFC6213] the [RFC5120] MTID MUST be used as specified in [RFC6213].
 An MI-RTR MUST NOT support [RFC5120] multi-topology within a non-zero
 instance when any non-zero ITID is supported.  The following TLVs
 MUST NOT be sent in an LSP associated with a non-zero instance that
 supports a non-zero ITID, and such an LSP MUST be ignored when
 received:
  TLV 222 - MT IS Neighbors
  TLV 235 - MT IP Reachability
  TLV 237 - MT IPv6 Reachability

Ginsberg, et al. Standards Track [Page 11] RFC 8202 IS-IS Multi-Instance June 2017

6. 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 all of the topology-specific LSP databases 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.

7. IANA Considerations

 IANA has registered an IS-IS TLV, reflected in the "IS-IS TLV
 Codepoints Registry":
  Value  Name                   IIH  LSP  SNP  Purge
  ----   ---------------------  ---  ---  ---  -----
   7     Instance Identifier     y    y    y     y
 Per [RFC6822], IANA has registered two EUI-48 multicast addresses
 from the IANA-managed EUI address space as specified in [RFC7042].
 The addresses are as follows:
    01-00-5E-90-00-02 AllL1MI-ISs
    01-00-5E-90-00-03 AllL2MI-ISs
 All references to [RFC6822] in the "IS-IS TLV Codepoints Registry"
 and the "IANA Multicast 48-bit MAC Addresses" registry have been
 replaced by references to this document.

8. Security Considerations

 Security concerns for IS-IS are addressed in [ISO10589], [RFC5304],
 and [RFC5310].

9. References

9.1. Normative References

 [ISO10589]
            International Organization for Standardization,
            "Information technology -- Telecommunications and
            information exchange between systems -- 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,
            November 2002.

Ginsberg, et al. Standards Track [Page 12] RFC 8202 IS-IS Multi-Instance June 2017

 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119,
            DOI 10.17487/RFC2119, March 1997,
            <http://www.rfc-editor.org/info/rfc2119>.
 [RFC5120]  Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
            Topology (MT) Routing in Intermediate System to
            Intermediate Systems (IS-ISs)", RFC 5120,
            DOI 10.17487/RFC5120, February 2008,
            <http://www.rfc-editor.org/info/rfc5120>.
 [RFC5303]  Katz, D., Saluja, R., and D. Eastlake 3rd, "Three-Way
            Handshake for IS-IS Point-to-Point Adjacencies", RFC 5303,
            DOI 10.17487/RFC5303, October 2008,
            <http://www.rfc-editor.org/info/rfc5303>.
 [RFC5304]  Li, T. and R. Atkinson, "IS-IS Cryptographic
            Authentication", RFC 5304, DOI 10.17487/RFC5304, October
            2008, <http://www.rfc-editor.org/info/rfc5304>.
 [RFC5306]  Shand, M. and L. Ginsberg, "Restart Signaling for IS-IS",
            RFC 5306, DOI 10.17487/RFC5306, October 2008,
            <http://www.rfc-editor.org/info/rfc5306>.
 [RFC5310]  Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
            and M. Fanto, "IS-IS Generic Cryptographic
            Authentication", RFC 5310, DOI 10.17487/RFC5310, February
            2009, <http://www.rfc-editor.org/info/rfc5310>.
 [RFC6213]  Hopps, C. and L. Ginsberg, "IS-IS BFD-Enabled TLV",
            RFC 6213, DOI 10.17487/RFC6213, April 2011,
            <http://www.rfc-editor.org/info/rfc6213>.
 [RFC6232]  Wei, F., Qin, Y., Li, Z., Li, T., and J. Dong, "Purge
            Originator Identification TLV for IS-IS", RFC 6232,
            DOI 10.17487/RFC6232, May 2011,
            <http://www.rfc-editor.org/info/rfc6232>.
 [RFC6233]  Li, T. and L. Ginsberg, "IS-IS Registry Extension for
            Purges", RFC 6233, DOI 10.17487/RFC6233, May 2011,
            <http://www.rfc-editor.org/info/rfc6233>.
 [RFC6822]  Previdi, S., Ed., Ginsberg, L., Shand, M., Roy, A., and D.
            Ward, "IS-IS Multi-Instance", RFC 6822,
            DOI 10.17487/RFC6822, December 2012,
            <http://www.rfc-editor.org/info/rfc6822>.

Ginsberg, et al. Standards Track [Page 13] RFC 8202 IS-IS Multi-Instance June 2017

 [RFC6823]  Ginsberg, L., Previdi, S., and M. Shand, "Advertising
            Generic Information in IS-IS", RFC 6823,
            DOI 10.17487/RFC6823, December 2012,
            <http://www.rfc-editor.org/info/rfc6823>.
 [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
            2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
            May 2017, <http://www.rfc-editor.org/info/rfc8174>.

9.2. Informative References

 [Err4519]  RFC Errata, Erratum ID 4519, RFC 6822.
 [Err4520]  RFC Errata, Erratum ID 4520, RFC 6822.
 [RFC5309]  Shen, N., Ed. and A. Zinin, Ed., "Point-to-Point Operation
            over LAN in Link State Routing Protocols", RFC 5309,
            DOI 10.17487/RFC5309, October 2008,
            <http://www.rfc-editor.org/info/rfc5309>.
 [RFC7042]  Eastlake 3rd, D. and J. Abley, "IANA Considerations and
            IETF Protocol and Documentation Usage for IEEE 802
            Parameters", BCP 141, RFC 7042, DOI 10.17487/RFC7042,
            October 2013, <http://www.rfc-editor.org/info/rfc7042>.

Ginsberg, et al. Standards Track [Page 14] RFC 8202 IS-IS Multi-Instance June 2017

Appendix A. Changes to RFC 6822

 RFC 6822 prohibited the use of Multi-Topology (MT) support as
 described in RFC 5120 in a non-zero instance.  However, deployment
 experience since the writing of RFC 6822 has revealed a desire to be
 able to support the style of MT in RFC 5120 using multiple non-zero
 instances as an alternative means of controlling leaking of
 information between L1 areas while also supporting incongruent
 topologies for different address families.  The rules have therefore
 been relaxed to allow use of MT per RFC 5120 in a non-zero instance
 so long as ITID #0 is the only instance topology (ITID) supported by
 the instance.  Note that this change is not backwards compatible with
 implementations strictly following RFC 6822.  As of this writing, all
 known implementations are compatible with this change.
 A suggestion has been added to place the IID-TLV as the first TLV in
 a PDU to speed recognition of the correct instance when parsing a
 received PDU.
 Clarification that when operating in point-to-point mode on a
 broadcast circuit the IID-TLV is only included in point-to-point IIHs
 associated with non-zero instances has been added.  This addresses
 Errata ID 4519 [Err4519].
 Clarification of the appropriate MAC multicast addresses to use when
 sending PDUs on a broadcast interface for both standard instance and
 non-zero instances has been provided.  This addresses Errata ID 4520
 [Err4520].

Acknowledgements

 The authors greatly acknowledge Mike Shand, Abhay Roy, and Dave Ward
 for their contributions as coauthors of RFC 6822.  In addition, we
 note that RFC 6822 acknowledged contributions made by Dino Farinacci
 and Tony Li.
 The authors of this document would also like to thank Paul Wells.

Ginsberg, et al. Standards Track [Page 15] RFC 8202 IS-IS Multi-Instance June 2017

Authors' Addresses

 Les Ginsberg
 Cisco Systems
 821 Alder Drive
 Milpitas, CA  95035
 United States of America
 Email: ginsberg@cisco.com
 Stefano Previdi
 Cisco Systems
 Via Del Serafico 200
 Rome  0144
 Italy
 Email: sprevidi@cisco.com
 Wim Henderickx
 Nokia
 Belgium
 Email: wim.henderickx@nokia.com

Ginsberg, et al. Standards Track [Page 16]

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