This section describes how MPLS OAM models the SR tunnel types.
An SR shortest path tunnel, SR-ISIS tunnel, or SR-OSPF tunnel uses a single FEC element in the target FEC stack TLV. The FEC corresponds to the prefix of the SID in a specific IGP instance.
Figure: IPv4 IGP prefix SID shows the format for the IPv4 IGP prefix SID.
The fields are defined as follows:
IPv4 Prefix
This field carries the IPv4 prefix to which the SID is assigned. For an anycast SID, this field carries the IPv4 anycast address. If the prefix is shorter than 32 bits, trailing bits must be set to 0.
Prefix Length
This field is one octet and gives the length of the prefix in bits (values can be from 1 to 32).
Protocol
This field is set to 1 when the IGP is OSPF and set to 2 when the IGP is IS-IS.
Figure: IPv6 IGP prefix SID shows the format for the IPv6 IGP prefix SID.
The fields are defined as follows:
IPv6 Prefix
This field carries the IPv6 prefix to which the SID is assigned. For an anycast SID, this field carries the IPv4 anycast address. If the prefix is shorter than 128 bits, trailing bits must be set to 0.
Prefix Length
This field is one octet and gives the length of the prefix in bits (values can be from 1 to 128).
Protocol
This field is set to 1 when the IGP protocol is OSPF and set to 2 when the IGP protocol is IS-IS.
As a hierarchical LSP, an SR-TE LSP uses the target FEC stack TLV, which contains a FEC element for each node SID and each adjacency SID in the path of the SR-TE LSP. Because the SR-TE LSP does not instantiate a state in the LSR other than the ingress LSR, MPLS OAM tests a hierarchy of node SID and adjacency SID segments toward the destination of the SR-TE LSP. Figure: IPv6 IGP prefix SID shows the format for the node SID. Figure: IGP Adjacency SID shows the format for the IGP Adjacency SID.
The fields are defined as follows:
Adj. Type (Adjacency Type)
This field is set to 1 when the adjacency segment is a parallel adjacency as defined in draft.ietf-spring-segment-routing. This field is set to 4 when the adjacency segment is IPv4-based and is not a parallel adjacency. This field is set to 6 when the adjacency segment is IPv6-based and is not a parallel adjacency.
Protocol
This field is set to 1 when the IGP protocol is OSPF and set to 2 when the IGP protocol is IS-IS.
Local Interface ID
This field is an identifier that is assigned by the local LSR for a link on which the adjacency SID is bound. This field is set to a local link address (IPv4 or IPv6). If unnumbered, the 32-bit link identifier defined in RFC 4203 and RFC 5307 is used. If the adjacency SID represents parallel adjacencies, as described in draft.ietf-spring-segment-routing, this field must be set to 0.
Remote Interface ID
This field is an identifier that is assigned by the remote LSR for a link on which the adjacency SID is bound. This field is set to the remote (downstream neighbor) link address (IPv4 or IPv6). If unnumbered, the 32-bit link identifier defined in RFC 4203 and RFC 5307 is used. If the adjacency SID represents parallel adjacencies, as described in draft.ietf-spring-segment-routing, this field must be set to 0.
Advertising Node Identifier
This field specifies the advertising node identifier. When the Protocol field is set to 1, the 32 rightmost bits represent the OSPF router ID. When the Protocol field is set to 2, this field carries the 48-bit IS-IS system ID.
Receiving Node Identifier
This field specifies the downstream node identifier. When the Protocol field is set to 1, the 32 rightmost bits represent the OSPF router ID. When the Protocol field is set to 2, this field carries the 48-bit IS-IS system ID.
Both lsp-ping and lsp-trace apply to the following contexts:
SR-ISIS or SR-OSPF shortest path IPv4 tunnel
SR-ISIS shortest path IPv6 tunnel
IS-IS SR-TE IPv4 LSP or OSPF SR-TE IPv4 LSP
BGP IPv4 LSP resolved over an SR-ISIS IPv4 tunnel, an SR-OSPF IPv4 tunnel, or an SR-TE IPv4 LSP, including support for BGP LSP across AS boundaries and for ECMP next hops at the transport tunnel level