8.2.1. Constructing Ethernet A-D per Ethernet Segment Route

8.2.1. Constructing Ethernet A-D per Ethernet Segment Route

This section describes the procedures used to construct the Ethernet A-D per ES route, which is used for fast convergence (as discussed above) and for advertising the ESI label used for split-horizon filtering (as discussed in Section 8.3). Support of this route is REQUIRED.

The Route Distinguisher (RD) MUST be a Type 1 RD [RFC4364]. The value field comprises an IP address of the PE (typically, the loopback address) followed by a number unique to the PE.

The Ethernet Segment Identifier MUST be a 10-octet entity as described in Section 5 ("Ethernet Segment"). The Ethernet A-D route is not needed when the Segment Identifier is set to 0 (e.g., single homed scenarios).

The Ethernet Tag ID MUST be set to MAX-ET.

The MPLS label in the NLRI MUST be set to 0.

The ESI Label extended community MUST be included in the route. If All-Active redundancy mode is desired, then the "Single-Active" bit in the flags of the ESI Label extended community MUST be set to 0 and the MPLS label in that Extended Community MUST be set to a valid MPLS label value. The MPLS label in this Extended Community is referred to as the ESI label and MUST have the same value in each Ethernet A-D per ES route advertised for the ES. This label MUST be a downstream assigned MPLS label if the advertising PE is using ingress replication for receiving multicast, broadcast, or unknown unicast traffic from other PEs. If the advertising PE is using P2MP MPLS LSPs for sending multicast, broadcast, or unknown unicast traffic, then this label MUST be an upstream assigned MPLS label. The usage of this label is described in Section 8.3.

If Single-Active redundancy mode is desired, then the "Single-Active" bit in the flags of the ESI Label extended community MUST be set to 1 and the ESI label SHOULD be set to a valid MPLS label value.