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8.3.1.1. Ingress Replication

8.3.1.1. Ingress Replication​

Each PE that operates in All-Active or Single-Active redundancy mode and that uses ingress replication to receive BUM traffic advertises a downstream assigned ESI label in the set of Ethernet A-D per ES routes for its attached ES. This label MUST be programmed in the platform label space by the advertising PE, and 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.

The rules for the inclusion of the ESI label in a BUM packet by the ingress PE operating in All-Active redundancy mode are as follows:

  • A non-DF ingress PE MUST include the ESI label distributed by the DF egress PE in the copy of a BUM packet sent to it.

  • An ingress PE (DF or non-DF) SHOULD include the ESI label distributed by each non-DF egress PE in the copy of a BUM packet sent to it.

The rule for the inclusion of the ESI label in a BUM packet by the ingress PE operating in Single-Active redundancy mode is as follows:

  • An ingress DF PE SHOULD include the ESI label distributed by the egress PE in the copy of a BUM packet sent to it.

In both All-Active and Single-Active redundancy mode, an ingress PE MUST NOT include an ESI label in the copy of a BUM packet sent to an egress PE that is not attached to the ES through which the BUM packet entered the EVI.

As an example, consider PE1 and PE2, which are multihomed to CE1 on ES1 and operating in All-Active multihoming mode. Further, consider that PE1 is using P2P or MP2P LSPs to send packets to PE2. Consider that PE1 is the non-DF for VLAN1 and PE2 is the DF for VLAN1, and PE1 receives a BUM packet from CE1 on VLAN1 on ES1. In this scenario, PE2 distributes an Inclusive Multicast Ethernet Tag route for VLAN1 corresponding to an EVPN instance. So, when PE1 sends a BUM packet that it receives from CE1, it MUST first push onto the MPLS label stack the ESI label that PE2 has distributed for ES1. It MUST then push onto the MPLS label stack the MPLS label distributed by PE2 in the Inclusive Multicast Ethernet Tag route for VLAN1. The resulting packet is further encapsulated in the P2P or MP2P LSP label stack required to transmit the packet to PE2. When PE2 receives this packet, it determines, from the top MPLS label, the set of ESIs to which it will replicate the packet after any P2P or MP2P LSP labels have been removed. If the next label is the ESI label assigned by PE2 for ES1, then PE2 MUST NOT forward the packet onto ES1. If the next label is an ESI label that has not been assigned by PE2, then PE2 MUST drop the packet. It should be noted that in this scenario, if PE2 receives a BUM packet for VLAN1 from CE1, then it SHOULD encapsulate the packet with an ESI label received from PE1 when sending it to PE1 in order to avoid any transient loops during a failure scenario that would impact ES1 (e.g., port or link failure).

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