Symmetric
Explanation:
Understanding IRB (Integrated Routing and Bridging) Forwarding in VXLAN VXLAN (Virtual Extensible LAN) supports Layer 2 and Layer 3 forwarding between Virtual Network Identifiers (VNIs).
* IRB (Integrated Routing and Bridging) enables inter-subnet communication within a VXLAN fabric.
* There are two 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 IRB requires both ingress and egress VTEPs to perform Layer 3 lookups.
* The ingress VTEP (source gateway) performs a Layer 2 MAC lookup, then a Layer 3 lookup to find the destination VTEP.
* The egress VTEP (destination gateway) performs another Layer 3 lookup before forwarding the packet to the destination.
# Asymmetric IRB does not perform two lookups at the ingress VTEP:
* In Asymmetric IRB, the ingress VTEP performs both Layer 2 and Layer 3 forwarding and sends a Layer 2 packet to the egress VTEP.
* The egress VTEP only does a Layer 2 lookup, not a Layer 3 lookup.
* Since the question states that both L2 and L3 lookups occur at the ingress VTEP, asymmetric IRB is incorrect.
# Why Symmetric IRB is More Common?
* Scalability: Supports any-to-any communication across VXLAN networks.
* More Efficient Routing: Uses Layer 3 VXLAN encapsulation, ensuring efficient routing between VNIs.
# Reference: Huawei HCIE Datacom - VXLAN Symmetric and Asymmetric IRB Forwarding