BGP MPLS-Based Ethernet VPN (EVPN) was created to address limitations in highly successful MPLS LDP-based VPLS. While the initial standard specifically addresses IP/MPLS networks, EVPN will also be available on Segment Routing networks. Limitations in LDP-based VPLS were identified in areas such as: “multihoming and redundancy, multicast optimization, provisioning simplicity, flow-based load balancing, and multipathing”.
In addition to the benefits of EVPN compared to LDP-based VPLS, basing VPLS on BGP provides a similar approach for Layer 3 IP VPNs and Layer 2 Ethernet VPNs. This has operational synergy benefits as well as service migration benefits. EVPN has the ability to communicate IP prefixes without any associated Ethernet MAC address, enabling the creation of IP VPN topologies and constructs. Whether a EVPN-based L3VPN is a full/satisfactory substitute for Service Provider based WAN Enterprise services is a currently a matter of differing opinions. If EVPN can evolve over time to be a general approach to L3VPN, outside of data center use cases, then it will drive increased value as a single approach for L2 and L3 VPNs, depending on your view of using BGP for multiple control plane tasks.
EVPN is supported by major Routing vendors, and is generally viewed today as the future of L2 VPN services. As noted, whether it is the future of L3 VPN services is currently a matter of debate and we will have to observe how this plays out.
- Simplification: Unified control plane for many forwarding plane encapsulations
- All-Active multi-homing (dual-homing, triple-homing, quad-homing,..)
- Auto-discover access devices, type of network attached, and PEs
- broadcast and multicast traffic is sent using a shared multicast tree or with ingress replication
- Control plane learning: MAC address learning requires the flooding of unknown unicast and ARP frames, whereas IP address learning does not require any flooding.
- Aliasing: per-flow load-balancing to all multi-homing PE devices, even if a specific MAC/IP address is learned by only one of the multi-homing PEs.
- Fast convergence through mass MAC address withdraw, realized through route withdraw and transition to another PE.
- Optimum forwarding: intra and inter-subnet
- Loop prevention for single and multi-homed devices
- Support for Anycast
- BGP MPLS-Based Ethernet VPN
- Requirements for Ethernet VPN (EVPN)
- Multiprotocol Extensions for BGP-4
- BGP Extended Communities Attribute
- Constrained Route Distribution for Border Gateway Protocol/MultiProtocol Label Switching (BGP/MPLS) Internet Protocol (IP) Virtual Private Networks (VPNs)
- BGP Encodings and Procedures for Multicast in MPLS/BGP IP VPNs