Understanding IRB (Integrated Routing and Bridging) Forwarding in VXLAN
VXLAN (Virtual Extensible LAN) supportsLayer 2 and Layer 3 forwardingbetween Virtual Network Identifiers (VNIs).
IRB (Integrated Routing and Bridging)enables inter-subnet communication within a VXLAN fabric.
There aretwo modes of IRB forwarding:
Symmetric IRB
Asymmetric IRB
Why the Answer is "Symmetric" IRB Forwarding?
✔Ingress VTEP performs both Layer 2 and Layer 3 lookups:
Symmetric IRBrequiresboth ingress and egress VTEPsto performLayer 3 lookups.
Theingress VTEP (source gateway) performs a Layer 2 MAC lookup, then aLayer 3 lookupto find the destination VTEP.
Theegress VTEP (destination gateway) performs another Layer 3 lookupbefore forwarding the packet to the destination.
✔Asymmetric IRB does not perform two lookups at the ingress VTEP:
In Asymmetric IRB,the ingress VTEPperforms both Layer 2 and Layer 3 forwardingandsends a Layer 2 packet to the egress VTEP.
Theegress VTEP only does a Layer 2 lookup, not a Layer 3 lookup.
Since thequestion states that both L2 and L3 lookups occur at the ingress VTEP,asymmetric IRB is incorrect.
✔Why Symmetric IRB is More Common?
Scalability:Supportsany-to-any communicationacross VXLAN networks.
More Efficient Routing:UsesLayer 3 VXLAN encapsulation, ensuring efficient routing between VNIs.
????Reference:Huawei HCIE Datacom – VXLAN Symmetric and Asymmetric IRB Forwarding
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