EVPN E-Tree Overview

You can use the Ethernet VPN (EVPN) Ethernet-Tree (E-Tree) feature to create a rooted-multipoint service supported with EVPN-MPLS in the core, as defined by the Metro Ethernet Forum (MEF) in RFC 8317. In an EVPN E-Tree service, you categorize interfaces as either root or leaf interfaces in a routing instance. You also define each customer edge (CE) device as a root or a leaf device. The EVPN E-Tree service follows these forwarding rules:

• A leaf can send or receive traffic only from a root.

• A root can send traffic to another root or any leaf.

Leaf and root CE devices can be single-homed or multihomed to the provider edge (PE) devices in the network.

The EVPN E-Tree service has all the benefits of EVPN such as all-active multihoming and load balancing loop detection for E-Tree.

In an EVPN E-Tree service, the forwarding rule depends on the traffic source and destination for known unicast traffic or unknown unicast, broadcast, and multicast (BUM) traffic. Table 1 shows the forwarding rules within the E-Tree service.

Note:

We don't support IGMP snooping, MLD snooping, or PIM snooping multicast optimizations with EVPN E-Tree.

Table 1: EVPN E-Tree Forwarding Rule Based on Traffic Source and Destination

Type of Traffic	Allowed/Not-Allowed	Filtering Location
Known Unicast Traffic from Root to Root	Allowed	-
Known Unicast Traffic from Root to Leaf	Allowed	-
BUM Traffic from Root to Root	Allowed	-
BUM Traffic from Root to Leaf	Allowed	-
Known Unicast Traffic from Leaf to Leaf	Not Allowed	At the ingress Packet Forwarding Engine
Known Unicast Traffic from Leaf to Root	Allowed	-
BUM Traffic from Leaf to Leaf	Not Allowed	At the Egress Packet Forwarding Engine
BUM Traffic from Leaf to Root	Allowed	-

If you don't configure a leaf or root role for an interface, it will be assigned the “root” role by default. All leaf interfaces are assigned a new mesh group with no local switching set to TRUE, which:

• Enables ingress filtering for unicast traffic.

• Drops all the leaf-to-leaf traffic at the ingress leaf interface.

For BUM traffic, the egress PE does the filtering based on the root or leaf label carried in the packet.