Home > Networking Solutions > Enterprise/Data Center Networking Solutions > SmartFabric OS10 Networking Solutions > Guides > OS10 10.5.1 Feature - Symmetric IRB - Technical Note > Comparing Symmetric and Asymmetric IRB
Asymmetric IRB has some benefits over Symmetric IRB, especially in a smaller data center deployment. The figure below compares the traffic flow in the data plane for each model.
Figure 2. Data plane traffic flow for Symmetric and Asymmetric IRB
The table below summarizes a feature comparison.
Table 1. Symmetric and Asymmetric IRB feature comparison
Symmetric IRB |
Asymmetric IRB |
Ingress VTEP needs only the MAC DA of the corresponding egress VTEP router. |
Ingress VTEP needs MAC DA of the end station to which the packet is destined. |
Egress VTEP routes after decapsulation. |
Egress VTEP only bridges after decapsulation. |
L3 VNI mapped to VRFs and many L2 VNIs mapped to a given VRF. Cannot be deployed in default VRF. |
No L3 VNI concept, however VRFs can be created for each tenant. Can be in default VRF as well. |
Centralized routing is not possible with Symmetric IRB. |
Centralized routing is possible with Asymmetric IRB. |
In terms of MAC/Route/ARP table usage, the Asymmetric IRB does not compare well with Symmetric IRB. Here the MAC and Neighbor tables in each VTEP must store end host information of the entire EVPN fabric. The ingress VTEP must know how to reach any host in the EVPN fabric as it does local route lookup for any/all destinations. Table 2 shows details:
Table 2. Mac/route table usage
Table |
Asymmetric IRB |
Symmetric IRB |
MAC Table |
All end hosts |
Only locally connected |
Neighbor Table |
All end hosts |
Only locally connected |
Route Table |
All end hosts |
All end hosts |
VNIs |
All VNIs in fabric |
Only locally connected |
Dell EMC has a more comprehensive BGP EVPN feature set than other vendors. As shown in the table below, Arista and Cisco do not implement Asymmetric IRB in their stack. Table 3 shows a comparison of various competitors’ EVPN IRB model implementations:
Table 3. Vendor comparison
Vendor |
Asymmetric |
Symmetric |
Arista |
No |
Yes |
Cisco |
No |
Yes |
Cumulus |
Yes |
Yes |
Dell |
Yes |
Yes |
Juniper |
Yes |
Yes |
Both Symmetric and Asymmetric IRB models have benefits and limitations. The following scenarios may help you choose the appropriate model for your BGP EVPN fabric deployment.
Scenarios for using Symmetric IRB:
Scenarios for using Asymmetric IRB: