4. EVPN Features

4. EVPN Features

EVPN [RFC7432] was originally designed to support the requirements detailed in [RFC7209] and therefore has the following attributes which directly address control-plane scaling and ease of deployment issues.

1. Control-plane information is distributed with BGP and broadcast and multicast traffic is sent using a shared multicast tree or with ingress replication.

2. Control-plane learning is used for MAC (and IP) addresses instead of data-plane learning. The latter requires the flooding of unknown unicast and Address Resolution Protocol (ARP) frames; whereas, the former does not require any flooding.

3. Route Reflector (RR) is used to reduce a full mesh of BGP sessions among PE devices to a single BGP session between a PE and the RR. Furthermore, RR hierarchy can be leveraged to scale the number of BGP routes on the RR.

4. Auto-discovery via BGP is used to discover PE devices participating in a given VPN, PE devices participating in a given redundancy group, tunnel encapsulation types, multicast tunnel types, multicast members, etc.

5. All-Active multihoming is used. This allows a given Customer Edge (CE) device to have multiple links to multiple PEs, and traffic to/from that CE fully utilizes all of these links.

6. When a link between a CE and a PE fails, the PEs for that EVI are notified of the failure via the withdrawal of a single EVPN route. This allows those PEs to remove the withdrawing PE as a next hop for every MAC address associated with the failed link. This is termed "mass withdrawal".

7. BGP route filtering and constrained route distribution are leveraged to ensure that the control-plane traffic for a given EVI is only distributed to the PEs in that EVI.

8. When an IEEE 802.1Q [IEEE.802.1Q] interface is used between a CE and a PE, each of the VLAN IDs (VIDs) on that interface can be mapped onto a bridge table (for up to 4094 such bridge tables). All these bridge tables may be mapped onto a single MAC-VRF (in case of VLAN-aware bundle service).

9. VM Mobility mechanisms ensure that all PEs in a given EVI know the ES with which a given VM, as identified by its MAC and IP addresses, is currently associated.

10. RTs are used to allow the operator (or customer) to define a spectrum of logical network topologies including mesh, hub and spoke, and extranets (e.g., a VPN whose sites are owned by different enterprises), without the need for proprietary software or the aid of other virtual or physical devices.

Because the design goal for NVO is millions of instances per common physical infrastructure, the scaling properties of the control plane for NVO are extremely important. EVPN and the extensions described herein, are designed with this level of scalability in mind.