Segment Routing Segment Types Extensions for BGP SR Policy

The Segment List sub-TLV encodes a single explicit path towards the endpoint as described in section 5.1 of . The Segment List sub-TLV includes the elements of the paths (i.e., segments). A Segment sub-TLV describes a single segment in a segment list (i.e., a single element of the explicit path). Section 4 of defines several Segment Types:

specifies Segment Type Sub-TLVs for the segment types A and B. The following sub-sections specify the sub-TLVs used for encoding each of the other Segment Types above. As specified in section 2.4.4.2 of , the Segment Type Sub-TLVs specified in this document are also used only by the Segment Routing Policy Module (SRPM) as described in section 4 of along the same lines as segment types A and B. Their validation is, therefore, beyond the scope of BGP.

The Type C Segment Sub-TLV encodes an IPv4 node address, SR Algorithm, and an optional SR-MPLS SID. The format is as follows:

Type: 3. Length: Specifies the length of the value field (i.e., not including Type and Length fields) in terms of octets. The value MUST be 10 when the SR-MPLS SID is present else it MUST be 6. Flags: 1 octet of flags as defined in . SR Algorithm: 1 octet specifying SR Algorithm as described in section 3.1.1 in when A-Flag as defined in is present. SR Algorithm is used by SRPM as described in section 4 in . When A-Flag is not encoded, this field MUST be set to zero on transmission and MUST be ignored on receipt. IPv4 Node Address: a 4-octet IPv4 address representing a node. SR-MPLS SID: optional, 4-octet field containing label, TC, S and TTL as defined for Segment Type A .

The Type D Segment Sub-TLV encodes an IPv6 node address, SR Algorithm, and an optional SR-MPLS SID. The format is as follows:

Type: 4 Length: Specifies the length of the value field (i.e., not including Type and Length fields) in terms of octets. The value MUST be 22 when the SR-MPLS SID is present else it MUST be 18. Flags: 1 octet of flags as defined in . SR Algorithm: 1 octet specifying SR Algorithm as described in section 3.1.1 in when A-Flag as defined in is present. SR Algorithm is used by SRPM as described in section 4 in . When A-Flag is not encoded, this field MUST be set to zero on transmission and MUST be ignored on receipt. IPv6 Node Address: a 16-octet IPv6 address representing a node. SR-MPLS SID: optional, 4-octet field containing label, TC, S and TTL as defined for Segment Type A .

The Type E Segment Sub-TLV encodes an IPv4 node address, a local interface Identifier (Local Interface ID), and an optional SR-MPLS SID. The format is as follows:

Type: 5. Length: Specifies the length of the value field (i.e., not including Type and Length fields) in terms of octets. The value MUST be 14 when the SR-MPLS SID is present else it MUST be 10. Flags: 1 octet of flags as defined in . RESERVED: 1 octet of reserved bits. This field MUST be set to zero on transmission and MUST be ignored on receipt. Local Interface ID: 4 octets of interface index of local interface (refer TLV 258 of ). IPv4 Node Address: a 4-octet IPv4 address representing a node. SR-MPLS SID: optional, 4-octet field containing label, TC, S and TTL as defined for Segment Type A .

The Type F Segment Sub-TLV encodes an adjacency local address, an adjacency remote address, and an optional SR-MPLS SID. The format is as follows:

Type: 6. Length: Specifies the length of the value field (i.e., not including Type and Length fields) in terms of octets. The value MUST be 14 when the SR-MPLS SID is present else it MUST be 10. Flags: 1 octet of flags as defined in . RESERVED: 1 octet of reserved bits. This field MUST be set to zero on transmission and MUST be ignored on receipt. Local IPv4 Address: a 4-octet IPv4 address representing the local link address of the node. Remote IPv4 Address: a 4-octet IPv4 address representing the link address of the neighbor node. SR-MPLS SID: optional, 4-octet field containing label, TC, S and TTL as defined for Segment Type A .

The Type G Segment Sub-TLV encodes an IPv6 link-local adjacency with IPv6 local node address, a local interface identifier (Local Interface ID), IPv6 remote node address, a remote interface identifier (Remote Interface ID), and an optional SR-MPLS SID. The format is as follows:

Type: 7 Length: Specifies the length of the value field (i.e., not including Type and Length fields) in terms of octets. The value MUST be 46 when the SR-MPLS SID is present else it MUST be 42. Flags: 1 octet of flags as defined in . RESERVED: 1 octet of reserved bits. This field MUST be set to zero on transmission and MUST be ignored on receipt. Local Interface ID: 4 octets of interface index of local interface (refer TLV 258 of ). IPv6 Local Node Address: a 16-octet IPv6 address representing the node. Remote Interface ID: 4 octets of interface index of remote interface (refer TLV 258 of ). The value MAY be set to zero when the local node address and interface identifiers are sufficient to describe the link. IPv6 Remote Node Address: a 16-octet IPv6 address. The value MAY be set to zero when the local node address and interface identifiers are sufficient to describe the link. SR-MPLS SID: optional, 4-octet field containing label, TC, S and TTL as defined for Segment Type A .

The Type H Segment Sub-TLV encodes an adjacency local address, an adjacency remote address, and an optional SR-MPLS SID. The format is as follows:

Type: 8 Length: Specifies the length of the value field (i.e., not including Type and Length fields) in terms of octets. The value MUST be 38 when the SR-MPLS SID is present else it MUST be 34. Flags: 1 octet of flags as defined in . RESERVED: 1 octet of reserved bits. This field MUST be set to zero on transmission and MUST be ignored on receipt. Local IPv6 Address: a 16-octet IPv6 address representing the local link address of the node. Remote IPv6 Address: a 16-octet IPv6 address representing the link address of the neighbor node. SR-MPLS SID: optional, 4-octet field containing label, TC, S and TTL as defined for Segment Type A .

The Type I Segment Sub-TLV encodes an IPv6 node address, SR Algorithm, and an optional SRv6 SID. The format is as follows:

Type: 14 Length: Specifies the length of the value field (i.e., not including Type and Length fields) in terms of octets. The value MUST be one of: 42 when both SRv6 SID and SRv6 Endpoint Behavior & SID Structure are present, 34 when only SRv6 SID is present, or 18 when the SRv6 SID is not present. Flags: 1 octet of flags as defined in . SR Algorithm: 1 octet specifying SR Algorithm as described in section 3.1.1 in when A-Flag as defined in is present. SR Algorithm is used by SRPM as described in section 4 in . When A-Flag is not encoded, this field MUST be set to zero on transmission and MUST be ignored on receipt. IPv6 Node Address: a 16-octet IPv6 address representing the node. SRv6 SID: optional, a 16-octet IPv6 address. SRv6 Endpoint Behavior and SID Structure: Optional, as defined in for Segment Type B. The TLV 10 defined for the advertisement of Segment Type I in the early draft versions of has been deprecated to avoid backward compatibility issues.

The Type J Segment Sub-TLV encodes an IPv6 link-local adjacency with local node address, a local interface identifier (Local Interface ID), remote IPv6 node address, a remote interface identifier (Remote Interface ID), and an optional SRv6 SID. The format is as follows:

Type: 15 Length: Specifies the length of the value field (i.e., not including Type and Length fields) in terms of octets. The value MUST be one of: 66 when both SRv6 SID and SRv6 Endpoint Behavior & SID Structure are present, 58 when only SRv6 SID is present, or 42 when the SRv6 SID is not present. Flags: 1 octet of flags as defined in . SR Algorithm: 1 octet specifying SR Algorithm as described in section 3.1.1 in when A-Flag as defined in is present. SR Algorithm is used by SRPM as described in section 4 in . When A-Flag is not encoded, this field MUST be set to zero on transmission and MUST be ignored on receipt. Local Interface ID: 4 octets of interface index of local interface (refer TLV 258 of ). IPv6 Local Node Address: a 16-octet IPv6 address representing the node. Remote Interface ID: 4 octets of interface index of remote interface (refer TLV 258 of ). The value MAY be set to zero when the local node address and interface identifiers are sufficient to describe the link. IPv6 Remote Node Address: a 16-octet IPv6 address. The value MAY be set to zero when the local node address and interface identifiers are sufficient to describe the link. SRv6 SID: optional, a 16-octet IPv6 address. SRv6 Endpoint Behavior and SID Structure: Optional, as defined in for Segment Type B. The TLV 11 defined for the advertisement of Segment Type J in the early draft versions of has been deprecated to avoid backward compatibility issues.

The Type K Segment Sub-TLV encodes an adjacency local address, an adjacency remote address, and an optional SRv6 SID. The format is as follows:

Type: 16 Length: Specifies the length of the value field (i.e., not including Type and Length fields) in terms of octets. The value MUST be one of: 58 when both SRv6 SID and SRv6 Endpoint Behavior & SID Structure are present, 50 when only SRv6 SID is present, or 34 when the SRv6 SID is not present. Flags: 1 octet of flags as defined in . SR Algorithm: 1 octet specifying SR Algorithm as described in section 3.1.1 in when A-Flag as defined in is present. SR Algorithm is used by SRPM as described in section 4 in . When A-Flag is not encoded, this field MUST be set to zero on transmission and MUST be ignored on receipt. Local IPv6 Address: a 16-octet IPv6 address representing the local link address of the node. Remote IPv6 Address: a 16-octet IPv6 address representing the link address of the neighbor node. SRv6 SID: optional, a 16-octet IPv6 address. SRv6 Endpoint Behavior and SID Structure: Optional, as defined in for Segment Type B. The TLV 12 defined for the advertisement of Segment Type K in the early draft versions of has been deprecated to avoid backward compatibility issues.

The Segment Types sub-TLVs described above may contain the following flags in the "Segment Flags" field defined in . This document introduces additional flags as below:

where: V-Flag: existing flag as defined in . A-Flag: This flag, when set, indicates the presence of SR Algorithm id in the "SR Algorithm" field applicable to various Segment Types. SR Algorithm is used by SRPM as described in section 4 of . S-Flag: This flag, when set, indicates the presence of the SR-MPLS or SRv6 SID depending on the segment type. B-Flag: existing flag as defined in . The following applies to the Segment Flags: V-Flag applies to all Segment Types including the ones introduced by this document. A-Flag applies to Segment Types C, D, I, J, and K. If A-Flag appears with Segment Types A, B, E, F, G, and H, it MUST be ignored. S-Flag applies to Segment Types C, D, E, F, G, H, I, J, and K. If S-Flag appears with Segment Types A or B, it MUST be ignored. B-Flag applies to Segment Types B, I, J, and K. If B-Flag appears with Segment Types A, C, D, E, F, G, and H, it MUST be ignored.