China Mobile

China gongliyan@chinamobile.com

New H3C Technologies

China linchangwang.04414@h3c.com

New H3C Technologies

China huxiaolong.1260@outlook.com

Cisco Systems

United States of America ginsberg@cisco.com

Cisco Systems

Apollo Business Center Mlynske nivy 43 Bratislava 821 09 Slovakia ppsenak@cisco.com

Routing LSR Working Group OSPF, IS-IS, BGP-LS, Layer 2 Bundle, Link Aggregation In networks where Layer 2 (L2) interface bundles (such as a Link Aggregation Group (LAG) as defined in IEEE 802.1AX) are deployed, a controller may need to collect the connectivity relationships between bundle members for traffic engineering (TE) purposes. For example, when performing topology management and bidirectional path computation for TE, it is essential to know the connectivity relationships among bundle members. This document describes how OSPF and IS-IS would advertise the remote interface identifiers for Layer 2 bundle members. The corresponding extension of BGP Link State (BGP-LS) is also specified.

Introduction BGP Link State (BGP-LS) is widely used for collecting topology information from IGPs. In networks where Layer 2 (L2) interface bundles (such as a Link Aggregation Group (LAG) ) are deployed, a controller may need to collect the connectivity relationships between bundle members for traffic engineering (TE) purposes. For example, when performing topology management and bidirectional path computation for TE (e.g., for a co-routed associated bidirectional path as defined in Section 2.2.2 of or Section 3.3 of ), knowledge of the connectivity relationships among bundle members is required. When advertising L2 bundles in OSPF and IS-IS , a member link is described by its local interface identifier, also referred to as a link local identifier. If the remote interface identifier could be advertised for each member link, the pairing relationships between the local and remote interfaces would be clear. This document describes the mechanism for advertising the remote interface identifier for Layer 2 bundle members in OSPF and IS-IS. The BGP-LS extension for advertising L2 bundle member interface remote identifier is also specified in this document.

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.

Use Case shows a network, in which an L2 bundle is deployed between R1 and R2. The controller collects the topology information from R3 via BGP-LS.

Network Topology with L2 Bundle

The network operator may want to control bidirectional traffic flows on the individual member links of the underlying Layer 2 bundle for TE purposes. The real-time bandwidth, delay, and link loss might be measured for each bundle member at both ends. Labels or Segment Identifiers (SIDs) might be allocated for each bundle member at both ends. So, there would be requirements for the controller to figure out the connectivity relationships between bundle members. This document defines a mechanism for Interior Gateway Protocol (IGP) routers to advertise the remote interface identifiers for each L2 bundle member, along with the corresponding mechanism for the controller to collect such information via BGP-LS.

Advertising L2 Bundle Member Remote Interface Identifier The routers at both ends of the LAG (e.g., R1 and R2 in ) independently advertise their local member interface information along with the corresponding remote interface identifiers. The following subsections describe how the remote interface identifiers of L2 bundle members are advertised in OSPF, IS-IS, and BGP-LS, respectively. The L2 bundle member information is advertised in association with the parent L3 link (i.e., the logical link directly operated on by the Layer 3 protocol, as distinguished from the individual L2 bundle member links which are not directly visible to Layer 3). The descriptions in this section are intended to be illustrative and are not meant to be normative. The normative definitions of the L2 Bundle Member Attributes TLV and its sub-TLVs are provided in for OSPF, for IS-IS, and for BGP-LS. Note that the term "sub-TLV" is used throughout this document (consistent with the referenced RFCs) to refer to TLVs that are nested within a parent TLV.

OSPF Advertisement In OSPF, the remote interface identifiers of L2 bundle members are advertised as follows. OSPFv2 Extended Link TLV, or OSPFv3 Router-Link TLV, for the parent L3 link:

IS-IS Advertisement In IS-IS, the remote interface identifiers of L2 bundle members are advertised as follows. Note that IS-IS can advertise a set of members in a single L2 Bundle Member Attribute Descriptor, so the L2 Bundle Member Interface Remote Identifier sub-TLV MUST carry multiple remote interface identifiers, one for each of the bundle members advertised in the associated L2 Bundle Member Descriptor.

BGP-LS Advertisement In BGP-LS, the remote interface identifiers of L2 bundle members are advertised as follows. R2 (as described in Section 5.2 of [RFC9086]) Link Attributes: L2 Bundle Member Attributes TLV: L2 Bundle Member Descriptor of Member #1 L2 Bundle Member Interface Remote Identifier sub-TLV (Optional - as defined in Section 6) L2 Bundle Member Attributes TLV: L2 Bundle Member Descriptor of Member #2 L2 Bundle Member Interface Remote Identifier sub-TLV (Optional - as defined in Section 6) ... L2 Bundle Member Attributes TLV: L2 Bundle Member Descriptor of Member #n L2 Bundle Member Interface Remote Identifier sub-TLV (Optional - as defined in Section 6) ]]>

OSPF Extension This document defines a new L2 Bundle Member Interface Remote Identifier sub-TLV in both OSPFv2 and OSPFv3. This sub-TLV is used to advertise the remote interface identifier for a L2 bundle member. It can be carried as a sub-TLV of the OSPF L2 Bundle Member Attributes TLV . It has the following format:

Type:

TBA (to be assigned from the "OSPFv2 Extended Link TLV Sub-TLVs" registry and the "OSPFv3 Extended-LSA Sub-TLVs" registry).

Length:

4.

Remote Interface ID:

Remote identifier of interface, 4 octets. See for the definition of the remote interface identifier and details on how this value is obtained.

A remote interface ID with value of zero is not valid and MUST be ignored and handled as if the sub-TLV was not present. The L2 Bundle Member Interface Remote Identifier sub-TLV MUST NOT appear more than once within the same L2 Bundle Member Attributes TLV. If multiple instances of this sub-TLV are received within the same L2 Bundle Member Attributes TLV, implementations MUST use the first occurrence and ignore subsequent occurrences.

IS-IS Extension This document defines a new L2 Bundle Member Interface Remote Identifier sub-TLV in IS-IS. This sub-TLV is used to advertise the remote interface identifiers for L2 bundle members. It can be carried as a sub-TLV of the IS-IS L2 Bundle Member Attributes TLV . It has the following format:

Type:

TBA (to be assigned from the "IS-IS Sub-TLVs for TLVs Advertising Neighbor Information" registry).

Length:

4 * Number of L2 Bundle Member Descriptors.

Remote Interface ID:

Remote identifier of interface, 4 octets. See for the definition of the remote interface identifier and details on how this value is obtained.

There MUST be one Remote Interface ID for each of the L2 Bundle Members advertised under the associated L2 Bundle Member Attribute Descriptor. The Remote Interface IDs are ordered such that the first Remote Interface ID corresponds to the first bundle member listed in the L2 Bundle Member Descriptor, the second Remote Interface ID corresponds to the second bundle member, and so on. A remote interface ID with value of zero MUST be ignored and handled as if the value was unknown. The L2 Bundle Member Interface Remote Identifier sub-TLV MUST NOT appear more than once within the same L2 Bundle Member Attributes TLV. If multiple instances of this sub-TLV are received within the same L2 Bundle Member Attributes TLV (e.g., during transient conditions), implementations MUST use the first occurrence in the lowest numbered Link State Protocol Data Unit (LSP) fragment and ignore subsequent occurrences. MP-TLV for the new IS-IS sub-TLV SHOULD be set to "N".

BGP-LS Extension This document defines a new L2 Bundle Member Interface Remote Identifier sub-TLV in BGP-LS. This sub-TLV is derived from the Remote Interface Identifier sub-TLV of OSPF (Section 3) and IS-IS (Section 4). It can be carried as a sub-TLV of the BGP-LS L2 Bundle Member Attributes TLV . It has the following format:

Type:

TBA (to be assigned from the "BGP-LS NLRI and Attribute TLVs" registry).

Length:

4.

Remote Interface ID:

Remote identifier of interface, 4 octets. See for the definition of the remote interface identifier and details on how this value is obtained.

A remote interface ID with value of zero is not valid and MUST be ignored and handled as if the sub-TLV was not present. The L2 Bundle Member Interface Remote Identifier sub-TLV MUST NOT appear more than once within the same L2 Bundle Member Attributes TLV. If multiple instances of this sub-TLV are received within the same L2 Bundle Member Attributes TLV, implementations MUST use the first occurrence and ignore subsequent occurrences.

Acquirement of Remote Interface Identifier IGPs have no direct way to exchange L2 bundle member link identifiers since the Layer 3 protocol is not operating directly on the bundle members. The remote interface identifiers can be obtained via Layer 2 protocols as described below. The remote interface identifier is the value of the interface identifier that is assigned by the router at the remote end of the link to its own local interface (i.e., the local interface identifier of the remote router for that bundle member). The interface identifier is defined in . The RECOMMENDED method for acquiring remote interface identifiers is to use LLDP (Link Layer Discovery Protocol, ). When LLDP is enabled on bundle members, each router can learn the neighbor's port identifier from the Port ID TLV in LLDP frames. This port identifier SHOULD be used as the remote interface identifier in the advertisements described in this document. Alternatively, the remote interface identifiers MAY be obtained through IEEE 802.1AX () Link Aggregation Control Protocol (LACP) negotiation, where the Actor and Partner Port Identifiers can be used to derive the remote interface identifiers. To verify the correctness of the acquired remote interface identifiers, implementations SHOULD provide mechanisms to validate that the identifier pairs are consistent. For example, if R1 advertises remote ID X for its local member with ID A, then R2 (the neighbor) SHOULD advertise remote ID A for its local member with ID X. Mismatched pairs may indicate misconfiguration or incorrect discovery.

Operational Considerations Implementations MUST NOT enable the advertisement of L2 bundle member Interface Remote Identifier sub-TLV by default and MUST provide a configuration option to enable their advertisement on specific links.

Security Considerations This document describes how OSPF, IS-IS and BGP-LS would advertise the remote interface identifiers for Layer 2 bundle members. There are no new security issues introduced by the extensions in this document. The security considerations of , , , and are applicable to this document. If the IS-IS 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. If the OSPF protocol is used in an environment where unauthorized access to the physical links on which OSPF packets are sent occurs, then attacks are possible. The use of authentication as defined in , , , and is recommended for preventing such attacks. The isolation of BGP-LS peering sessions is recommended to ensure that BGP-LS topology information (including the newly added remote interface identifiers information) is not advertised to an external BGP peering session outside the trusted domain .

IANA Considerations This document adds the following new sub-TLV to the "OSPFv2 Extended Link TLV Sub-TLVs" registry. This document adds the following new sub-TLV to the "OSPFv3 Extended-LSA Sub-TLVs" registry. This document adds the following new sub-TLV to the "IS-IS Sub-TLVs for TLVs Advertising Neighbor Information" registry. This document adds the following new sub-TLV to the "BGP-LS NLRI and Attribute TLVs" registry.

Acknowledgements The authors would like to thank Acee Lindem for his shepherd review and helpful comments to improve this document. The authors would like to thank Michael Richardson for RTGDIR early review. The authors would also like to thank Shraddha Hegde, and Tom Petch for their review of this document and their comments.

Resource Reservation Protocol (RSVP) association signaling can be used to bind two unidirectional Label Switched Paths (LSPs) into an associated bidirectional LSP. When an associated bidirectional LSP is co-routed, the reverse LSP follows the same path as its forward LSP. This document updates the fast reroute procedures defined in RFC 4090 to support both single-sided and double-sided provisioned associated bidirectional LSPs. This document also updates the procedure for associating two reverse LSPs defined in RFC 7551 to support co-routed bidirectional LSPs. The fast reroute procedures can ensure that, for the co-routed LSPs, traffic flows on co-routed paths in the forward and reverse directions after a failure event. This document defines Path Computation Element Communication Protocol (PCEP) extensions for grouping two unidirectional MPLS-TE Label Switched Paths (LSPs), one in each direction in the network, into an associated bidirectional LSP. These PCEP extensions can be applied either using a stateful PCE for both PCE-initiated and PCC-initiated LSPs or using a stateless PCE. The PCEP procedures defined are applicable to the LSPs using RSVP-TE for signaling.

Contributors Cisco Systems

India ketant.ietf@gmail.com