Dell EMC SmartFabric OS10 User Guide Release 10.5.1

Symmetric IRB routing

In symmetric IRB routing, both ingress and egress VTEPs perform IRB routing and bridging for a tenant subnet. The ingress VTEP routes packets to an egress VTEP MAC address in an intermediate virtual-network VNI. The egress VTEP then routes the packet again to the destination host in the destination virtual-network VNI.

Using the L3 VNI associated with each tenant VRF, an ingress VTEP routes all traffic for the prefix to an egress VTEP on the L3 VNI. The egress VTEP routes from the L3 VNI to the destination virtual network or bridge domain. The L3 VNI does not have to be associated with an IP address; routing is set up in the data plane using the egress VTEP's MAC address. This behavior is known as IP-VRF to IP-VRF interface-less routing.

The ingress VTEP does not have to be configured with every destination virtual network; it must have the ARP and MAC addresses only to the egress VTEP, not to each host connected to the VTEP. For this reason, symmetric IRB routing allows the overlay network to scale larger than asymmetric routing. Assign the same router MAC address to each VLT peer in a VTEP VLT domain.

Each VTEP learns host MAC and MAC-to-IP bindings using ARP snooping for local addresses, and type-2 and type-5 route advertisements from remote VTEPs. In addition to L3 VNI-connected networks, type-5 route advertisements communicate external routes from a border leaf VTEP to all other VTEPs.

For a VXLAN BGP EVPN example that uses symmetric IRB and Type-5 route, see Example: VXLAN BGP EVPN — Symmetric IRB.