8.3.1.2. P2MP MPLS LSPs
8.3.1.2. P2MP MPLS LSPs
The non-DF PEs that operate in All-Active redundancy mode and that use P2MP LSPs to send BUM traffic advertise an upstream assigned ESI label in the set of Ethernet A-D per ES routes for their common attached ES. This label is upstream assigned by the PE that advertises the route. This label MUST be programmed by the other PEs that are connected to the ESI advertised in the route, in the context label space for the advertising PE. Further, the forwarding entry for this label must result in NOT forwarding packets received with this label onto the Ethernet segment for which the label was distributed. This label MUST also be programmed by the other PEs that import the route but are not connected to the ESI advertised in the route, in the context label space for the advertising PE. Further, the forwarding entry for this label must be a label pop with no other associated action.
The DF PE that operates in Single-Active redundancy mode and that uses P2MP LSPs to send BUM traffic should advertise an upstream assigned ESI label in the set of Ethernet A-D per ES routes for its attached ES, just as described in the previous paragraph.
As an example, consider PE1 and PE2, which are multihomed to CE1 on ES1 and operating in All-Active multihoming mode. Also, consider that PE3 belongs to one of the EVPN instances of ES1. Further, assume that PE1, which is the non-DF, is using P2MP MPLS LSPs to send BUM packets. When PE1 sends a BUM packet that it receives from CE1, it MUST first push onto the MPLS label stack the ESI label that it has assigned for the ESI on which the packet was received. The resulting packet is further encapsulated in the P2MP MPLS label stack necessary to transmit the packet to the other PEs. Penultimate hop popping MUST be disabled on the P2MP LSPs used in the MPLS transport infrastructure for EVPN. When PE2 receives this packet, it decapsulates the top MPLS label and forwards the packet using the context label space determined by the top label. If the next label is the ESI label assigned by PE1 to ES1, then PE2 MUST NOT forward the packet onto ES1. When PE3 receives this packet, it decapsulates the top MPLS label and forwards the packet using the context label space determined by the top label. If the next label is the ESI label assigned by PE1 to ES1 and PE3 is not connected to ES1, then PE3 MUST pop the label and flood the packet over all local ESIs in that EVPN instance. It should be noted that when PE2 sends a BUM frame over a P2MP LSP, it should encapsulate the frame with an ESI label even though it is the DF for that VLAN, in order to avoid any transient loops during a failure scenario that would impact ES1 (e.g., port or link failure).