BGP was standardized in RFC 7432 and RFC 8365 to carry Layer-2 information for virtualized networks. Ethernet virtual private network (EVPN) was initially targeted for MPLS and WAN, but later adopted as a VXLAN control plane protocol. ExtremeXOS supports EVPN control plane for VXLAN. At a high level, BGP supports the following constructs to distribute information for any virtualized network:
- Identify the network address family with AFI/SAFI—For VXLAN, AFI of 25 (L2VPN) and a SAFI (EVPN) of 70 is used.
- Within the address family, identify the type of route being advertised—Different route types are defined. For supported route types in ExtremeXOS, see Supported EVPN Route Types in ExtremeXOS.
- Identify which device originated the route and virtual-network the route belongs to—This is the role of the route distinguisher (RD) and route target (RT).
In ExtremeXOS, RD is automatically derived based on configured local-endpoint IP address and the VLAN ID of the tenant VLAN. The VLAN ID of the tenant VLAN is also used as an EVPN instance (EVI) index. An EVI is automatically created when a virtual network configuration is completed and BGP is enabled. A complete virtual-network consists of a tenant VLAN, VNI, and local endpoint IP address. RTs are automatically calculated for each EVI using the method specified in Section 184.108.40.206 of RFC-8365. Because this method uses the local AS number as part of the calculation, each router calculates different RTs in an EBGP environment because the local AS number is different.
NoteRTs are derived automatically under the following conditions:
- When iBGP is used and the AS number is less than 65,535 (2 byte ASNUM).
- BGP Auto-peering is used.
EVPN devices perform dynamic learning on the access side of a VXLAN network. The learned MAC and ARP entries are exported to BGP as EVPN Type 2 routes. BGP advertises the Type 2 routes to all neighbors with L2VPN-EVPN capability. A VTEP with matching RT configured or auto-derived processes these Type 2 routes and creates static non-permanent FDB, ARP tunnel entries. Traffic to the tunnel entries are VXLAN encapsulated and forwarded.