AOS-CX 10.09 VXLAN EVPN Guide Help Center
Symmetric IRB
Symmetric IRB uses the same Layer-3 VNI for bi-directional traffic between two hosts on different VLANs/VNIs. For example:
Figure 1 Symmetric IRB Topology
- Host1 in VLAN 10/VNI 10 connected to VTEP1 sends traffic to Host2 in VLAN 20/VNI 20 connected to VTEP2.
- Traffic from Host1 is sent to VTEP1 VLAN 10/ VNI 10 gateway MAC.
- VTEP1 routes traffic in the VRF (mapping to L3-VNI 1020), encapsulates traffic with VXLAN, adds outer Source/Destination IP, VNI info and sends traffic to VTEP2.
- VTEP1 does not need to have a MAC/ARP entry for Host2.
- VTEP1 learns the prefix route and/or host route corresponding to Host2 via EVPN Route type 5 or 2 respectively thus facilitating routing to the destination.
- The inner Source MAC is changed to VTEP1 router MAC and inner Destination MAC is changed to VTEP2 router MAC.
- VTEP2 decapsulates outer VXLAN, routes and sends the traffic to Host2 on VLAN 20/VNI 20.
- Host2 will see source MAC as VTEP2 gateway MAC.
Return traffic from Host2 to Host1 is similar, traffic from Host2 is sent to VTEP2 VLAN20/VNI 20 gateway MAC. VTEP2 routes traffic to L3 VNI 1020, encapsulates and sends the traffic to VTEP1. VTEP1 decapsulates, route and send the traffic to Host1 on VLAN 10/VNI 10.
As seen from the traffic flow:
- Routing is used on both ingress and egress VTEPs.
- Bi-directional traffic uses symmetric path; same L3 VNI in both directions.
- VTEPs do not need to hold unnecessary ARP/MAC resources.
- Destination VLAN/VNI does not have to be configured on source VTEP.