What are EVPN inclusive multicast Ethernet tag (IMET) routes used for?

The EVPN Inclusive Multicast Ethernet Tag (IMET) route, also known as EVPN Route Type 3, is used for the auto-discovery of Provider Edge (PE) routers participating in the same EVPN Instance (EVI) or VPLS service. Each PE advertises an IMET route to signal its membership in a specific VPLS. Other PEs in the same service receive this route and add the originating PE to their flood list. This mechanism is fundamental for establishing the necessary ingress replication tunnels to forward Broadcast, Unknown Unicast, and Multicast (BUM) traffic to all participating PEs within that service instance.

A. This is the function of the EVPN MAC/IP Advertisement route (Route Type 2), which communicates specific host reachability information.

B. This is handled by the EVPN Ethernet Segment route (Route Type 4), which is used for multi-homing redundancy and Designated Forwarder (DF) election.

D. Discovering PEs attached to the same multi-homed Ethernet Segment is the primary function of the Ethernet Auto-Discovery (A-D) per ES route (Route Type 1).

1. Nokia 7450 ESS, 7750 SR, 7950 XRS, and VSR Layer 2 Services and EVPN Guide, Release 22.10.R1, Document ID: 3HE 18121 AAAC TQZZA 01.

Section: EVPN-MPLS for VPLS services > EVPN route types

Quote/Paraphrase: "The inclusive multicast Ethernet tag route is used for BUM traffic. The route is also referred to as route type 3. The route advertisement is used by the remote PEs to build their flooding list for a specified VPLS service." This confirms the route is used for PEs to discover each other for the purpose of BUM traffic flooding within a service.

2. IETF RFC 7432: BGP MPLS-Based Ethernet VPN.

Section 8.3: Inclusive Multicast Ethernet Tag Route

Quote/Paraphrase: "A PE that is configured with a particular EVI MUST advertise an Inclusive Multicast Ethernet Tag route for that EVI. This route is used to advertise the tunnel endpoint for ingress replication... When a PE receives an Inclusive Multicast Ethernet Tag route, it MUST check if it is configured for the EVI associated with the route. If it is, the receiving PE adds the originator of the route to the flooding list for BUM traffic for that EVI." This directly supports the auto-discovery function for building BUM forwarding paths.