Overview
The EVPN-E-TREE service is a VPN service where each attachment circuit is designated as either root or leaf. The E-Tree service is a rooted-multipoint service that is supported with EVPN over MPLS in the core. An EVPN instance (EVI) contains Access Circuits (ACs) that connect to PEs that form the edge of the MPLS infrastructure. The PEs provide virtual Layer 2 bridged connectivity between the ACs.
The EVPN E-TREE feature provides a way to categorize the interfaces as either "root" or "leaf".
Benefits
The EVPN E-TREE service has all the benefits of EVPN. The EVPN control-plane MAC learning has the following benefits:
• Eliminate flood and learn mechanism as hosts are learned over control plane.
• OcNOS supports both dynamically learned hosts and statically configured hosts, which are advertised/learned over the EVPN control plane.
• Fast-reroute, resiliency, and faster convergence in case of multihoming
• Load balancing of traffic to and from CEs that are multihomed to multiple PE's.
The following E-TREE rules are supported:
• A leaf can send or receive traffic only from a root.
• A root can send traffic to another root or any of the leafs.
• A leaf or root can be connected to provider edge (PE) devices in singlehoming mode or multihoming mode.
• EVPN E-TREE VLAN-based/VLAN-Bundle-aware services are supported.
Limitations
1. EVPN E-TREE solution is achieved by managing route-targets (i.e., option A) and as per RFC8317 option B is preferred which is not yet implemented.
2. Same route-targets for a given VNI on all PE routers won't work, instead nodes should have separate RT's for same VPN instance and import export need to be managed properly as per the role (either Root / Leaf)
3. On one PE router for a given VPN/EVI context, either Root (or) Leaf should exist but both cannot co-exist.
Route Types
These EVPN route types are used for E-TREE Services
• Route Type 1: Ethernet Auto-Discovery (AD) Route
The Ethernet (AD) routes are advertised on per EVI and per ESI basis. These routes are sent per ES. They carry the list of EVIs that belong to the ES.
This route is advertised when multihomed CEs already exist.
• Route Type 2: MAC/IP Advertisement Route
The host's IP and MAC addresses are advertised to the peers within NLRI. The control plane learning of MAC addresses reduces unknown unicast flooding.
• Route Type 3: Inclusive Multicast Ethernet Tag Route
This route establishes the connection for broadcast, unknown unicast, and multicast (BUM) traffic from a source PE to a remote PE.
This route is advertised on per VLAN and per ESI basis.
• Route Type 4: Ethernet Segment Route
Ethernet segment routes enable to connect a CE device to two or PE devices.
Ethernet segment routes enable the discovery of connected PE devices that are connected to the same Ethernet segment.
Last modified date: 10/17/2023