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+Internet Engineering Task Force (IETF)                  L. Ginsberg, Ed.
+Request for Comments: 8668                           Cisco Systems, Inc.
+Category: Standards Track                                    A. Bashandy
+ISSN: 2070-1721                                             Unaffiliated
+                                                             C. Filsfils
+                                                     Cisco Systems, Inc.
+                                                              M. Nanduri
+                                                                  Oracle
+                                                                E. Aries
+                                                             Arrcus Inc.
+                                                           December 2019
+
+
+       Advertising Layer 2 Bundle Member Link Attributes in IS-IS
+
+Abstract
+
+   There are deployments where the Layer 3 interface on which IS-IS
+   operates is a Layer 2 interface bundle.  Existing IS-IS
+   advertisements only support advertising link attributes of the Layer
+   3 interface.  If entities external to IS-IS wish to control traffic
+   flows on the individual physical links that comprise the Layer 2
+   interface bundle, link attribute information about the bundle members
+   is required.
+
+   This document introduces the ability for IS-IS to advertise the link
+   attributes of Layer 2 (L2) Bundle Members.
+
+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
+   https://www.rfc-editor.org/info/rfc8668.
+
+Copyright Notice
+
+   Copyright (c) 2019 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
+   (https://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
+   2.  Requirements Language
+   3.  L2 Bundle Member Attributes TLV
+     3.1.  Parallel L3 Adjacencies
+     3.2.  Shared Attribute Sub-TLVs
+   4.  Advertising L2 Bundle Member Adj-SIDs
+     4.1.  L2 Bundle Member Adjacency Segment Identifier Sub-TLV
+     4.2.  L2 Bundle Member LAN Adjacency SID Sub-TLV
+   5.  IANA Considerations
+   6.  Security Considerations
+   7.  References
+     7.1.  Normative References
+     7.2.  Informative References
+   Appendix A.  Example Encoding
+   Acknowledgements
+   Contributors
+   Authors' Addresses
+
+1.  Introduction
+
+   There are deployments where the Layer 3 interface on which an IS-IS
+   adjacency is established is a Layer 2 interface bundle, for instance,
+   a Link Aggregation Group (LAG) [IEEE802.1AX].  This reduces the
+   number of adjacencies that need to be maintained by the routing
+   protocol in cases where there are parallel links between the
+   neighbors.  Entities external to IS-IS such as Path Computation
+   Elements (PCEs) [RFC4655] may wish to control traffic flows on
+   individual members of the underlying Layer 2 bundle.  In order to do
+   so, link attribute information about individual bundle members is
+   required.  The protocol extensions defined in this document provide
+   the means to advertise this information.
+
+   This document introduces a new TLV to advertise link attribute
+   information for each of the L2 Bundle Members that comprise the Layer
+   3 interface on which IS-IS operates.
+
+   [RFC8667] introduces a new link attribute, adjacency segment
+   identifier (Adj-SID), which can be used as an instruction to
+   forwarding to send traffic over a specific link.  This document
+   introduces additional sub-TLVs to advertise Adj-SIDs for L2 Bundle
+   Members.
+
+   Note that the new advertisements defined in this document are
+   intended to be provided to external (to IS-IS) entities.  The
+   following items are intentionally not defined and/or are outside the
+   scope of this document:
+
+   *  What link attributes will be advertised.  This is determined by
+      the needs of the external entities.
+
+   *  A minimum or default set of link attributes.
+
+   *  How these attributes are configured.
+
+   *  How the advertisements are used.
+
+   *  What impact the use of these advertisements may have on traffic
+      flow in the network.
+
+   *  How the advertisements are passed to external entities.
+
+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.  L2 Bundle Member Attributes TLV
+
+   A new TLV is introduced to advertise L2 Bundle Member attributes.
+   Although much of the information is identical to and uses the same
+   sub-TLVs included in Extended IS Neighbor advertisements (TLVs 22 and
+   222), a new TLV is used so that changes to the advertisement of the
+   L2 Bundle Member link attributes do not trigger unnecessary action by
+   the [ISO10589] Decision Process.
+
+   Advertisement of this information implies that the identified link is
+   a member of the L2 Bundle associated with the identified Parent L3
+   Neighbor and that the member link is operationally up.  Therefore,
+   advertisements MUST be withdrawn if the link becomes operationally
+   down or it is no longer a member of the identified L2 Bundle.
+
+   This new TLV utilizes the sub-TLV space defined for TLVs 22, 23, 141,
+   222, and 223.
+
+   The following new TLV is introduced:
+
+      L2 Bundle Member Attributes
+
+      Type: 25
+
+      Length: Number of octets to follow
+
+      Parent L3 Neighbor Descriptor
+
+         L3 Neighbor System ID + pseudonode ID (7 octets)
+
+         Flags:  1-octet field of the following flags:
+
+             0 1 2 3 4 5 6 7
+            +-+-+-+-+-+-+-+-+
+            |P|             |
+            +-+-+-+-+-+-+-+-+
+
+            where:
+
+            P-Flag:  When set to 1, one of the sub-TLVs described in
+                     Section 3.1 immediately follows the flags field.
+                     If the P-Flag is set to 0, then none of the sub-
+                     TLVs described in Section 3.1 are present.
+
+            Other bits:  MUST be zero when originated and ignored when
+                     received.
+
+      One or more L2 Bundle Attribute Descriptors (as defined below).
+
+         Length of L2 Bundle Attribute Descriptor (1 octet)
+
+            NOTE: This includes all fields described below.
+
+         Number of L2 Bundle Member Descriptors (1 octet)
+
+         L2 Bundle Member Link Local Identifiers
+         (4 * Number of L2 Bundle Member Descriptors octets)
+
+            NOTE: An L2 Bundle Member Descriptor is a Link Local
+            Identifier as defined in [RFC4202].
+
+         Sub-TLV(s)
+         A sub-TLV may define an attribute common to all of the bundle
+         members listed, or it may define an attribute unique to each
+         bundle member.  Use of these two classes of sub-TLVs is
+         described in the following sections.
+
+      NOTE: Only one Parent L3 Neighbor Descriptor is present in a given
+      TLV.  Multiple L2 Bundle Attribute Descriptors may be present in a
+      single TLV.
+
+3.1.  Parallel L3 Adjacencies
+
+   When there exist multiple L3 adjacencies to the same neighbor,
+   additional information is required to uniquely identify the L3
+   Neighbor.  One and only one of the following three sub-TLVs is used
+   to uniquely identify the L3 adjacency:
+
+   *  IPv4 Interface Address (sub-TLV 6 defined in [RFC5305])
+
+   *  IPv6 Interface Address (sub-TLV 12 defined in [RFC6119])
+
+   *  Link Local/Remote Identifiers (sub-TLV 4 defined in [RFC5307])
+
+   When the P-Flag is set in the flags field in the Parent L3 Neighbor
+   Descriptor, one and only one of the above sub-TLVs MUST be present.
+   The chosen sub-TLV MUST immediately follow the flags field described
+   in Section 3.
+
+   These sub-TLVs MAY be omitted if no parallel adjacencies to the
+   neighbor exist.
+
+3.2.  Shared Attribute Sub-TLVs
+
+   These sub-TLVs advertise a single copy of an attribute (e.g., link
+   bandwidth).  The attribute applies to all of the L2 Bundle Members in
+   the set advertised under the preceding L2 Bundle Member Attribute
+   Descriptor.  No more than one copy of a given sub-TLV in this
+   category may appear in the set of sub-TLVs under the preceding L2
+   Bundle Member Attribute Descriptor.  If multiple copies of a given
+   sub-TLV are present, all copies MUST be ignored.
+
+   The set of L2 Bundle Member Descriptors that may be advertised under
+   a single L2 Bundle Member Attribute Descriptor is therefore limited
+   to bundle members that share the set of attributes advertised in the
+   shared attribute sub-TLVs.
+
+   All existing sub-TLVs defined in the IANA registry for Sub-TLVs for
+   TLVs 22, 23, 141, 222, and 223 are in the category of shared
+   attribute sub-TLVs unless otherwise specified in this document.
+
+4.  Advertising L2 Bundle Member Adj-SIDs
+
+   [RFC8667] defines sub-TLVs to advertise Adj-SIDs for L3 adjacencies.
+   However, these sub-TLVs only support the advertisement of a single
+   Adj-SID.  As it is expected that each L2 Bundle Member will have
+   unique Adj-SIDs in many deployments, it is desirable to define a new
+   sub-TLV that allows more efficient encoding of a set of Adj-SIDs in a
+   single sub-TLV.  Two new sub-TLVs are therefore introduced to support
+   advertising Adj-SIDs for L2 Bundle Members.  The format of the new
+   sub-TLVs is similar to that used for L3 adjacencies, but it is
+   optimized to allow advertisement of a set of Adj-SIDs (one per L2
+   Bundle Member) in a single sub-TLV.
+
+   The two new sub-TLVs defined in the following sections do not fall
+   into the category of shared attribute sub-TLVs.
+
+4.1.  L2 Bundle Member Adjacency Segment Identifier Sub-TLV
+
+   This sub-TLV is used to advertise Adj-SIDs for L2 Bundle Members
+   associated with a parent L3 adjacency that is point-to-point.  The
+   following format is defined for this sub-TLV:
+
+      Type:  41 (1 octet)
+
+      Length:  variable (1 octet)
+
+      Flags:  1-octet field of the following flags:
+
+          0 1 2 3 4 5 6 7
+         +-+-+-+-+-+-+-+-+
+         |F|*|V|L|S|P|   |
+         +-+-+-+-+-+-+-+-+
+
+         where:
+
+         F-Flag:  Address-Family Flag.  If unset, then the Adj-SID
+                  refers to an L2 Bundle Member with outgoing IPv4
+                  encapsulation.  If set, then the Adj-SID refers to an
+                  L2 Bundle Member with outgoing IPv6 encapsulation.
+
+         V-Flag:  Value Flag.  If set, then the Adj-SID carries a value.
+                  By default, the flag is SET.
+
+         L-Flag:  Local Flag.  If set, then the value/index carried by
+                  the Adj-SID has local significance.  By default, the
+                  flag is SET.
+
+         S-Flag:  Set Flag.  When set, the S-Flag indicates that the
+                  Adj-SID refers to a set of L2 Bundle Members (and
+                  therefore MAY be assigned to other L2 Bundle Members
+                  as well).
+
+         P-Flag:  Persistent Flag.  When set, the P-Flag indicates that
+                  the Adj-SID is persistently allocated, i.e., the Adj-
+                  SID value remains consistent across router restart
+                  and/or interface flap.
+
+         Other bits:  MUST be zero when originated and ignored when
+                  received.
+
+         NOTE: The flags are deliberately kept congruent to the flags in
+         the L3 ADJ-SID defined in [RFC8667].  * indicates a flag used
+         in the L3 Adj-SID sub-TLV, but one that is NOT used in this
+         sub-TLV.  These bits SHOULD be sent as 0 and MUST be ignored on
+         receipt.
+
+      Weight:  1 octet.  The value represents the weight of the Adj-SID
+               for the purpose of load balancing.  The use of the weight
+               is defined in [RFC8402].
+
+      NOTE: Flags and weight are shared by all L2 Bundle Members listed
+      in the L2 Bundle Attribute Descriptor.
+
+      L2 Bundle Member Adj-SID Descriptors:
+         There MUST be one descriptor for each of the L2 Bundle Members
+         advertised under the preceding L2 Bundle Member Attribute
+         Descriptor.  Each descriptor consists of one of the following
+         fields:
+
+      SID/Index/Label:  According to the V- and L-Flags, it contains
+         either:
+
+         o  A 3-octet local label where the 20 rightmost bits are used
+            for encoding the label value.  In this case, the V- and
+            L-Flags MUST be set.
+
+         o  A 4-octet index defining the offset in the SID/Label space
+            advertised by this router.  See [RFC8667].  In this case, V-
+            and L-Flags MUST be unset.
+
+4.2.  L2 Bundle Member LAN Adjacency SID Sub-TLV
+
+   This sub-TLV is used to advertise Adj-SIDs for L2 Bundle Members
+   associated with a parent L3 adjacency that is a LAN adjacency.  In
+   LAN subnetworks, the Designated Intermediate System (DIS) is elected
+   and originates the Pseudonode-LSP (PN-LSP) including all neighbors of
+   the DIS.  When Segment Routing is used, each router in the LAN MAY
+   advertise the Adj-SID of each of its neighbors on the LAN.
+   Similarly, for each L2 Bundle Member, a router MAY advertise an Adj-
+   SID to each neighbor on the LAN.
+
+   The following format is defined for this sub-TLV:
+
+      Type:  42 (1 octet)
+
+      Length:  variable (1 octet)
+
+      Neighbor System ID:  6 octets
+
+      Flags:  1-octet field of the following flags:
+
+          0 1 2 3 4 5 6 7
+         +-+-+-+-+-+-+-+-+
+         |F|*|V|L|S|P|   |
+         +-+-+-+-+-+-+-+-+
+
+         where:
+
+         F-Flag:  Address-Family Flag.  If unset, then the Adj-SID
+                  refers to an L2 Bundle Member with outgoing IPv4
+                  encapsulation.  If set, then the Adj-SID refers to an
+                  L2 Bundle Member with outgoing IPv6 encapsulation.
+
+         V-Flag:  Value Flag.  If set, then the Adj-SID carries a value.
+                  By default, the flag is SET.
+
+         L-Flag:  Local Flag.  If set, then the value/index carried by
+                  the Adj-SID has local significance.  By default, the
+                  flag is SET.
+
+         S-Flag:  Set Flag.  When set, the S-Flag indicates that the
+                  Adj-SID refers to a set of L2 Bundle Members (and
+                  therefore MAY be assigned to other L2 Bundle Members
+                  as well).
+
+         P-Flag:  Persistent Flag.  When set, the P-Flag indicates that
+                  the Adj-SID is persistently allocated, i.e., the Adj-
+                  SID value remains consistent across router restart
+                  and/or interface flap.
+
+         Other bits:  MUST be zero when originated and ignored when
+                  received.
+
+         NOTE: The flags are deliberately kept congruent to the flags in
+         the L3 LAN Adjacency SID defined in [RFC8667].  * indicates a
+         flag used in the L3 Adj-SID sub-TLV, but one that is NOT used
+         in this sub-TLV.  These bits SHOULD be sent as 0 and MUST be
+         ignored on receipt.
+
+      Weight:  1 octet.  The value represents the weight of the Adj-SID
+               for the purpose of load balancing.  The use of the weight
+               is defined in [RFC8402].
+
+      NOTE: Flags and weight are shared by all L2 Bundle Members listed
+      in the L2 Bundle Attribute Descriptor.
+
+      L2 Bundle Member LAN Adjacency SID Descriptors:
+         There MUST be one descriptor for each of the L2 Bundle Members
+         advertised under the preceding L2 Bundle Member Attribute
+         Descriptor.  Each descriptor consists of one of the following
+         fields:
+
+      SID/Index/Label:  According to the V- and L-Flags, it contains
+         either:
+
+         o  A 3-octet local label where the 20 rightmost bits are used
+            for encoding the label value.  In this case, the V- and
+            L-Flags MUST be set.
+
+         o  A 4-octet index defining the offset in the SID/Label space
+            advertised by this router.  See [RFC8667].  In this case, V-
+            and L-Flags MUST be unset.
+
+5.  IANA Considerations
+
+   This document adds the following new TLV to the IS-IS "TLV Codepoints
+   Registry".
+
+   Value:  25
+
+   Name:  L2 Bundle Member Attributes
+
+   The name of the IANA registry for Sub-TLVs for TLVs 22, 23, 141, 222,
+   and 223 has been changed to include sub-TLV 25.  An additional column
+   has been added to the registry to indicate which sub-TLVs may appear
+   in the new L2 Bundle Member Attributes TLV.  The column for TLV 25
+   has one of the following three values:
+
+   y     sub-TLV may appear in TLV 25 but MUST NOT be shared by multiple
+         L2 Bundle Members
+
+   y(s)  sub-TLV may appear in TLV 25 and MAY be shared by multiple L2
+         Bundle Members
+
+   n     sub-TLV MUST NOT appear in TLV 25
+
+   The following table indicates the appropriate settings for all
+   currently defined sub-TLVs with regard to their use in the new L2
+   Bundle Member Attributes TLV.
+
+      +-------+-------------------------------------------+--------+
+      | Value | Description                               | TLV 25 |
+      +=======+===========================================+========+
+      | 3     | Administrative group (color)              | y(s)   |
+      +-------+-------------------------------------------+--------+
+      | 4     | Link Local/Remote Identifiers             | y(s)   |
+      +-------+-------------------------------------------+--------+
+      | 6     | IPv4 interface address                    | y(s)   |
+      +-------+-------------------------------------------+--------+
+      | 8     | IPv4 neighbor address                     | y(s)   |
+      +-------+-------------------------------------------+--------+
+      | 9     | Maximum link bandwidth                    | y(s)   |
+      +-------+-------------------------------------------+--------+
+      | 10    | Maximum reservable link bandwidth         | y(s)   |
+      +-------+-------------------------------------------+--------+
+      | 11    | Unreserved bandwidth                      | y(s)   |
+      +-------+-------------------------------------------+--------+
+      | 12    | IPv6 Interface Address                    | y(s)   |
+      +-------+-------------------------------------------+--------+
+      | 13    | IPv6 Neighbor Address                     | y(s)   |
+      +-------+-------------------------------------------+--------+
+      | 14    | Extended Administrative Group             | y(s)   |
+      +-------+-------------------------------------------+--------+
+      | 18    | TE Default metric                         | y(s)   |
+      +-------+-------------------------------------------+--------+
+      | 19    | Link-attributes                           | y(s)   |
+      +-------+-------------------------------------------+--------+
+      | 20    | Link Protection Type                      | y(s)   |
+      +-------+-------------------------------------------+--------+
+      | 21    | Interface Switching Capability Descriptor | y(s)   |
+      +-------+-------------------------------------------+--------+
+      | 22    | Bandwidth Constraints                     | y(s)   |
+      +-------+-------------------------------------------+--------+
+      | 23    | Unconstrained TE LSP Count (sub-)TLV      | y(s)   |
+      +-------+-------------------------------------------+--------+
+      | 24    | remote AS number                          | n      |
+      +-------+-------------------------------------------+--------+
+      | 25    | IPv4 remote ASBR Identifier               | n      |
+      +-------+-------------------------------------------+--------+
+      | 26    | IPv6 remote ASBR Identifier               | n      |
+      +-------+-------------------------------------------+--------+
+      | 27    | Interface Adjustment Capability           | y(s)   |
+      |       | Descriptor (IACD)                         |        |
+      +-------+-------------------------------------------+--------+
+      | 28    | MTU                                       | n      |
+      +-------+-------------------------------------------+--------+
+      | 29    | SPB-Metric                                | y(s)   |
+      +-------+-------------------------------------------+--------+
+      | 30    | SPB-A-OALG                                | y(s)   |
+      +-------+-------------------------------------------+--------+
+      | 33    | Unidirectional Link Delay                 | y      |
+      +-------+-------------------------------------------+--------+
+      | 34    | Min/Max Unidirectional Link Delay         | y      |
+      +-------+-------------------------------------------+--------+
+      | 35    | Unidirectional Delay Variation            | y      |
+      +-------+-------------------------------------------+--------+
+      | 36    | Unidirectional Link Loss                  | y      |
+      +-------+-------------------------------------------+--------+
+      | 37    | Unidirectional Residual Bandwidth         | y      |
+      +-------+-------------------------------------------+--------+
+      | 38    | Unidirectional Available Bandwidth        | y      |
+      +-------+-------------------------------------------+--------+
+      | 39    | Unidirectional Utilized Bandwidth         | y      |
+      +-------+-------------------------------------------+--------+
+      | 40    | RTM Capability                            | n      |
+      +-------+-------------------------------------------+--------+
+
+                                 Table 1
+
+   This document adds the following new sub-TLVs to the above registry.
+
+   +------+--------------------------+----+----+----+-----+-----+-----+
+   | Type | Description              | 22 | 23 | 25 | 141 | 222 | 223 |
+   +======+==========================+====+====+====+=====+=====+=====+
+   |  41  | L2 Bundle Member Adj-SID | n  | n  | y  |  n  |  n  |  n  |
+   +------+--------------------------+----+----+----+-----+-----+-----+
+   |  42  | L2 Bundle Member LAN     | n  | n  | y  |  n  |  n  |  n  |
+   |      | Adj-SID                  |    |    |    |     |     |     |
+   +------+--------------------------+----+----+----+-----+-----+-----+
+
+                                 Table 2
+
+6.  Security Considerations
+
+   The IS-IS protocol has supported the advertisement of link attribute
+   information, including link identifiers, for many years.  The
+   advertisements defined in this document are identical to existing
+   advertisements defined in [RFC4202], [RFC5305], [RFC8570], and
+   [RFC8667], but are associated with L2 links that are part of a bundle
+   interface on which the IS-IS protocol operates.  There are therefore
+   no new security issues introduced by the extensions in this document.
+
+   As always, if the protocol is used in an environment where
+   unauthorized access to the physical links on which IS-IS Protocol
+   Data Units (PDUs) are sent occurs, then attacks are possible.  The
+   use of authentication as defined in [RFC5304] and [RFC5310] is
+   recommended to prevent such attacks.
+
+7.  References
+
+7.1.  Normative References
+
+   [IEEE802.1AX]
+              IEEE, "IEEE Standard for Local and metropolitan area
+              networks -- Link Aggregation", IEEE 802.1AX,
+              <https://ieeexplore.ieee.org/document/7055197>.
+
+   [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.
+
+   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
+              Requirement Levels", BCP 14, RFC 2119,
+              DOI 10.17487/RFC2119, March 1997,
+              <https://www.rfc-editor.org/info/rfc2119>.
+
+   [RFC4202]  Kompella, K., Ed. and Y. Rekhter, Ed., "Routing Extensions
+              in Support of Generalized Multi-Protocol Label Switching
+              (GMPLS)", RFC 4202, DOI 10.17487/RFC4202, October 2005,
+              <https://www.rfc-editor.org/info/rfc4202>.
+
+   [RFC5304]  Li, T. and R. Atkinson, "IS-IS Cryptographic
+              Authentication", RFC 5304, DOI 10.17487/RFC5304, October
+              2008, <https://www.rfc-editor.org/info/rfc5304>.
+
+   [RFC5305]  Li, T. and H. Smit, "IS-IS Extensions for Traffic
+              Engineering", RFC 5305, DOI 10.17487/RFC5305, October
+              2008, <https://www.rfc-editor.org/info/rfc5305>.
+
+   [RFC5307]  Kompella, K., Ed. and Y. Rekhter, Ed., "IS-IS Extensions
+              in Support of Generalized Multi-Protocol Label Switching
+              (GMPLS)", RFC 5307, DOI 10.17487/RFC5307, October 2008,
+              <https://www.rfc-editor.org/info/rfc5307>.
+
+   [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, <https://www.rfc-editor.org/info/rfc5310>.
+
+   [RFC6119]  Harrison, J., Berger, J., and M. Bartlett, "IPv6 Traffic
+              Engineering in IS-IS", RFC 6119, DOI 10.17487/RFC6119,
+              February 2011, <https://www.rfc-editor.org/info/rfc6119>.
+
+   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
+              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
+              May 2017, <https://www.rfc-editor.org/info/rfc8174>.
+
+   [RFC8570]  Ginsberg, L., Ed., Previdi, S., Ed., Giacalone, S., Ward,
+              D., Drake, J., and Q. Wu, "IS-IS Traffic Engineering (TE)
+              Metric Extensions", RFC 8570, DOI 10.17487/RFC8570, March
+              2019, <https://www.rfc-editor.org/info/rfc8570>.
+
+   [RFC8667]  Previdi, S., Ed., Ginsburg, L., Ed., Filsfils, C.,
+              Bashandy, A., Gredler, H., and B. Decraene, "IS-IS
+              Extensions for Segment Routing", RFC 8667,
+              DOI 10.17487/RFC8667, December 2019,
+              <https://www.rfc-editor.org/info/rfc8667>.
+
+7.2.  Informative References
+
+   [RFC4655]  Farrel, A., Vasseur, JP., and J. Ash, "A Path Computation
+              Element (PCE)-Based Architecture", RFC 4655,
+              DOI 10.17487/RFC4655, August 2006,
+              <https://www.rfc-editor.org/info/rfc4655>.
+
+   [RFC8402]  Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
+              Decraene, B., Litkowski, S., and R. Shakir, "Segment
+              Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
+              July 2018, <https://www.rfc-editor.org/info/rfc8402>.
+
+Appendix A.  Example Encoding
+
+   Below is an example encoding of L2 Bundle advertisements in a case
+   where we have two parallel adjacencies to the same neighbor whose
+   system-id is 1234.1234.1234.00.  The two L2 bundles have the
+   following sets of attributes:
+
+   L3 Adjacency #1
+
+   L3 IPv4 local link address: 192.0.2.1
+
+   Four bundle members with the following attributes:
+
+           +-----+---------------+-----------+----------------+
+           | Num | Link Local ID | Bandwidth | Adj-SID/Weight |
+           +=====+===============+===========+================+
+           |  1  |   0x11111111  |     1G    |   0x11111/1    |
+           +-----+---------------+-----------+----------------+
+           |  2  |   0x11112222  |     1G    |   0x11112/1    |
+           +-----+---------------+-----------+----------------+
+           |  3  |   0x11113333  |    10G    |   0x11113/1    |
+           +-----+---------------+-----------+----------------+
+           |  4  |   0x11114444  |    10G    |   0x11114/1    |
+           +-----+---------------+-----------+----------------+
+
+                                 Table 3
+
+   L3 Adjacency #2
+
+   L3 IPv4 local link address: 192.0.2.2
+
+   Three bundle members with the following attributes:
+
+           +-----+---------------+-----------+----------------+
+           | Num | Link Local ID | Bandwidth | Adj-SID/Weight |
+           +=====+===============+===========+================+
+           |  1  |   0x22221111  |    10G    |    22221/1     |
+           +-----+---------------+-----------+----------------+
+           |  2  |   0x22222222  |    10G    |    22222/1     |
+           +-----+---------------+-----------+----------------+
+           |  3  |   0x22223333  |    10G    |    22223/1     |
+           +-----+---------------+-----------+----------------+
+
+                                 Table 4
+
+   This requires two TLVs, one for each L3 adjacency.
+
+   TLV for Adjacency #1:
+
+    0                   1
+    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |  Type(25)     | Length(64)    |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+   Parent L3 Neighbor Descriptor
+
+    0                   1                   2                   3
+    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   | Neighbor System-ID octets 1-4: 1234.1234                      |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   | System-ID octets 5-6: 1234    | P-node: 00    |1|0|0|0|0|0|0|0|
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+   IPv4 Interface Address Sub-TLV
+
+    0                   1
+    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |  Type(6)      | Length(4)     |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   | IPv4 address: 192.0.2.1                                       |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+   L2 Bundle Attribute Descriptors
+
+    0                   1                   2                   3
+    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |Len:9+6+10 = 25| # Desc: 2     |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   | Link Local Identifier Bundle Member #1: 0x11111111            |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   | Link Local Identifier Bundle Member #2: 0x11112222            |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+   Maximum Link Bandwidth Sub-TLV
+
+    0                   1                   2                   3
+    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |  Type(9)       | Length(4)    |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   | Bandwidth Value: 1G/8                                         |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+   L2 Bundle Member Adj-SID Sub-TLV
+
+    0                   1                   2                   3
+    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |  Type(41)     | Length(8)     |0|0|1|1|0|0|0|0| Weight: 1     |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   | Local Label Bundle Member #1: 0x11111         |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   | Local Label Bundle Member #2: 0x11112         |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+   L2 Bundle Attribute Descriptors
+
+    0                   1                   2                   3
+    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |Len:9+6+10 = 25| # Desc: 2     |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   | Link Local Identifier Bundle Member #3: 0x11113333            |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   | Link Local Identifier Bundle Member #4: 0x11114444            |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+   Maximum Link Bandwidth Sub-TLV
+
+    0                   1                   2                   3
+    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |  Type(9)       | Length(4)    |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   | Bandwidth Value: 10G/8                                        |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+   L2 Bundle Member Adj-SID Sub-TLV
+
+    0                   1                   2                   3
+    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |  Type(41)     | Length(8)     |0|0|1|1|0|0|0|0| Weight: 1     |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   | Local Label Bundle Member #3: 0x11113         |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   | Local Label Bundle Member #4: 0x11114         |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+   TLV for Adjacency #2:
+
+    0                   1
+    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |  Type(25)     | Length(46)    |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+   Parent L3 Neighbor Descriptor
+
+    0                   1                   2                   3
+    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   | Neighbor System-ID octets 1-4: 1234.1234                      |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   | System-ID octets 5-6: 1234    | P-node: 00    |1|0|0|0|0|0|0|0|
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+   IPv4 Interface Address Sub-TLV
+
+    0                   1
+    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |  Type(6)      | Length(4)     |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   | IPv4 address: 192.0.2.2                                       |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+   L2 Bundle Attribute Descriptors
+
+    0                   1                   2                   3
+    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |Len:13+6+13=32 | # Desc: 3     |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   | Link Local Identifier Bundle Member #1: 0x22221111            |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   | Link Local Identifier Bundle Member #2: 0x22222222            |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   | Link Local Identifier Bundle Member #3: 0x22223333            |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+   Maximum Link Bandwidth Sub-TLV
+
+    0                   1                   2                   3
+    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |  Type(9)       | Length(4)    |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   | Bandwidth Value: 10G/8                                        |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+   L2 Bundle Member Adj-SID Sub-TLV
+
+    0                   1                   2                   3
+    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |  Type(41)     | Length(11)    |0|0|1|1|0|0|0|0| Weight: 1     |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   | Local Label Bundle Member #1: 0x22221         |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   | Local Label Bundle Member #2: 0x22222         |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   | Local Label Bundle Member #3: 0x22223         |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+Acknowledgements
+
+   The authors would like to thank Jon Mitchell for his careful review.
+
+Contributors
+
+   The following people gave a substantial contribution to the content
+   of this document and should be considered coauthors:
+
+   Stefano Previdi
+   Huawei Technologies
+   Italy
+
+   Email: stefano@previdi.net
+
+Authors' Addresses
+
+   Les Ginsberg (editor)
+   Cisco Systems, Inc.
+
+   Email: ginsberg@cisco.com
+
+
+   Ahmed Bashandy
+   Unaffiliated
+   United States of America
+
+   Email: abashandy.ietf@gmail.com
+
+
+   Clarence Filsfils
+   Cisco Systems, Inc.
+
+   Email: cf@cisco.com
+
+
+   Mohan Nanduri
+   Oracle
+
+   Email: mohan.nanduri@oracle.com
+
+
+   Ebben Aries
+   Arrcus Inc.
+   2077 Gateway Place, Suite #400
+   San Jose, CA 95119
+   United States of America
+
+   Email: exa@arrcus.com