Advertising Layer 2 Bundle Member Link Attributes in IS-IS

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) . 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) 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. 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.

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 when, and only when, they appear in all capitals, as shown here.

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 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: where:

P-flag:
When set to 1, one of the sub-TLVs described in immediately follows the flags field. If the P-flag is set to 0, then none of the sub-TLVs described in are present.

Other bits:
MUST be zero when originated and ignored when received.

One or more L2 Bundle Attribute Descriptors (as defined below). 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.

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 )
IPv6 Interface Address (sub-TLV 12 defined in )
Link Local/Remote Identifiers (sub-TLV 4 defined in )

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 . These sub-TLVs MAY be omitted if no parallel adjacencies to the neighbor exist.

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.

Advertising L2 Bundle Member Adj-SIDs 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.

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: . * 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 . 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: * 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. * A 4-octet index defining the offset in the SID/Label space advertised by this router. See . In this case, V and L flags MUST be unset. ]]>

L2 Bundle Member LAN 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 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: . * 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 . NOTE: Flags and weight are shared by all L2 Bundle Members listed in the L2 Bundle Attribute Descriptor. L2 Bundle Member LAN 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: * 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. * A 4-octet index defining the offset in the SID/Label space advertised by this router. See . In this case, V and L flags MUST be unset. ]]>

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. This document adds the following new sub-TLVs to the above registry. Value: 41 Name: L2 Bundle Member Adj-SID This sub-TLV is allowed in the following TLVs: Value: 42 Name: L2 Bundle Member LAN Adj-SID This sub-TLV is allowed in the following TLVs:

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 , , , and , 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 and is recommended to prevent such attacks.

References Normative References 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) International Organization for Standardization IEEE Standard for Local and metropolitan area networks -- Link Aggregation IEEE IS-IS Extensions for Segment Routing Key words for use in RFCs to Indicate Requirement Levels In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. Routing Extensions in Support of Generalized Multi-Protocol Label Switching (GMPLS) This document specifies routing extensions in support of carrying link state information for Generalized Multi-Protocol Label Switching (GMPLS). This document enhances the routing extensions required to support MPLS Traffic Engineering (TE). [STANDARDS-TRACK] IS-IS Cryptographic Authentication This document describes the authentication of Intermediate System to Intermediate System (IS-IS) Protocol Data Units (PDUs) using the Hashed Message Authentication Codes - Message Digest 5 (HMAC-MD5) algorithm as found in RFC 2104. IS-IS is specified in International Standards Organization (ISO) 10589, with extensions to support Internet Protocol version 4 (IPv4) described in RFC 1195. The base specification includes an authentication mechanism that allows for multiple authentication algorithms. The base specification only specifies the algorithm for cleartext passwords. This document replaces RFC 3567. This document proposes an extension to that specification that allows the use of the HMAC-MD5 authentication algorithm to be used in conjunction with the existing authentication mechanisms. [STANDARDS-TRACK] IS-IS Extensions for Traffic Engineering This document describes extensions to the Intermediate System to Intermediate System (IS-IS) protocol to support Traffic Engineering (TE). This document extends the IS-IS protocol by specifying new information that an Intermediate System (router) can place in Link State Protocol Data Units (LSP). This information describes additional details regarding the state of the network that are useful for traffic engineering computations. [STANDARDS-TRACK] IS-IS Extensions in Support of Generalized Multi-Protocol Label Switching (GMPLS) This document specifies encoding of extensions to the IS-IS routing protocol in support of Generalized Multi-Protocol Label Switching (GMPLS). [STANDARDS-TRACK] IS-IS Generic Cryptographic Authentication This document proposes an extension to Intermediate System to Intermediate System (IS-IS) to allow the use of any cryptographic authentication algorithm in addition to the already-documented authentication schemes, described in the base specification and RFC 5304. IS-IS is specified in International Standards Organization (ISO) 10589, with extensions to support Internet Protocol version 4 (IPv4) described in RFC 1195. Although this document has been written specifically for using the Hashed Message Authentication Code (HMAC) construct along with the Secure Hash Algorithm (SHA) family of cryptographic hash functions, the method described in this document is generic and can be used to extend IS-IS to support any cryptographic hash function in the future. [STANDARDS-TRACK] IPv6 Traffic Engineering in IS-IS This document specifies a method for exchanging IPv6 traffic engineering information using the IS-IS routing protocol. This information enables routers in an IS-IS network to calculate traffic-engineered routes using IPv6 addresses. [STANDARDS-TRACK] IS-IS Traffic Engineering (TE) Metric Extensions In certain networks, such as, but not limited to, financial information networks (e.g., stock market data providers), network-performance criteria (e.g., latency) are becoming as critical to data-path selection as other metrics. This document describes extensions to IS-IS Traffic Engineering Extensions (RFC 5305). These extensions provide a way to distribute and collect network-performance information in a scalable fashion. The information distributed using IS-IS TE Metric Extensions can then be used to make path-selection decisions based on network performance. Note that this document only covers the mechanisms with which network-performance information is distributed. The mechanisms for measuring network performance or acting on that information, once distributed, are outside the scope of this document. This document obsoletes RFC 7810. Informative References A Path Computation Element (PCE)-Based Architecture Constraint-based path computation is a fundamental building block for traffic engineering systems such as Multiprotocol Label Switching (MPLS) and Generalized Multiprotocol Label Switching (GMPLS) networks. Path computation in large, multi-domain, multi-region, or multi-layer networks is complex and may require special computational components and cooperation between the different network domains. This document specifies the architecture for a Path Computation Element (PCE)-based model to address this problem space. This document does not attempt to provide a detailed description of all the architectural components, but rather it describes a set of building blocks for the PCE architecture from which solutions may be constructed. This memo provides information for the Internet community. Segment Routing Architecture Segment Routing (SR) leverages the source routing paradigm. A node steers a packet through an ordered list of instructions, called "segments". A segment can represent any instruction, topological or service based. A segment can have a semantic local to an SR node or global within an SR domain. SR provides a mechanism that allows a flow to be restricted to a specific topological path, while maintaining per-flow state only at the ingress node(s) to the SR domain. SR can be directly applied to the MPLS architecture with no change to the forwarding plane. A segment is encoded as an MPLS label. An ordered list of segments is encoded as a stack of labels. The segment to process is on the top of the stack. Upon completion of a segment, the related label is popped from the stack. SR can be applied to the IPv6 architecture, with a new type of routing header. A segment is encoded as an IPv6 address. An ordered list of segments is encoded as an ordered list of IPv6 addresses in the routing header. The active segment is indicated by the Destination Address (DA) of the packet. The next active segment is indicated by a pointer in the new routing header.

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: This requires two TLVs, one for each L3 adjacency. TLV for Adjacency #1: TLV for Adjacency #2

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: