Dell EMC SmartFabric OS10 User Guide Release 10.5.0

VXLAN BGP EVPN routing

This section describes how EVPN implements overlay routing between L2 segments associated with EVIs belonging to the same tenant on a VTEP. IETF draft draft-ietf-bess-evpn-inter-subnet-forwarding-05 describes EVPN inter-subnet forwarding, Integrated Routing and Bridging (IRB), and how to use EVPN with IP routing between L2 tenant domains.

You set up overlay routing by assigning a VRF to each tenant, creating a virtual-network interface, and assigning an IP subnet in the VRF to each virtual-network interface. The VTEP acts as the L3 gateway that routes traffic from one tenant subnet to another in the overlay before encapsulating it in the VXLAN header and transporting it over the underlay fabric. On virtual networks that associate with EVIs, EVPN IRB is enabled only after you create a virtual-network interface.

When you enable IRB for a virtual network/EVI, EVPN operation on each VTEP also advertises the local tenant IP-MAC bindings learned on the EVPN-enabled virtual networks to all other VTEPs. The local tenant IP-MAC bindings are learned from ARP or ICMPv6 protocol operation. They advertise as EVPN Type-2 BGP route updates to other VTEPs, each of whom then imports and installs them as ARP/IPv6 neighbor entries in the dataplane.

To enable efficient traffic forwarding on a VTEP, OS10 supports distributed gateway routing. A distributed gateway allows multiple VTEPs to act as the gateway router for a tenant subnet. The VTEP that is located nearest to a host acts as its gateway router.