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I've been trying to configure and understand how VXLAN/EVPN and Symmetric/Asymmetric IRB work together. My question is exactly about this link VXLAN Network with MP-BGP EVPN Control Plane - Cisco and the paragraph just above Figure 5

As shown in Figure 5, when a packet is sent from VNI A to VNI B, the ingress VTEP routes the packet to the Layer-3 VNI. It rewrites the inner destination MAC address to the egress VTEP’s router MAC address and encodes the Layer-3 VNI in the VXLAN header. After the egress VTEP receives the encapsulated VXLAN packet, it first decapsulates the packet by removing the VXLAN header. Then it looks at the inner packet header. Because the destination MAC address in the inner packet header is its own MAC address, it performs a Layer-3 routing lookup. The Layer-3 VNI in the VXLAN header provides the VRF context in which this routing lookup is performed.

I'm confused with the explanation, I guess when they refer to Layer-3 VNI they are talking about the VNI we declared below the VRF context (in the same document they used 39000 and 39010). If is that the case the corresponding interface VLAN of those VNI has no IP address, so how the traffic is routed? My other question is, for instance if we have only two VTEPs in the topology,  in the data-packet the destination IP address of the VXLAN header (outer header) is the same if we routed or bridged the traffic?


Everyone's tags (3)

Re: Layer-3 VNI in VXLAN/EVPN

Hi,I'm learning vxlan right now,so I'll try to answer your questions.

From my understanding,when the VTEP doing IRB,it does not need an ip address for l3 vni,it only uses the l3 vni MAC to encapsulate the packet(inner packet),the inner packet is like this:

   source mac:ingress vtep router mac   dest mac:egress vtep router mac

   source ip:source user ip      dest ip:dest user ip

As for your other question,I think the answer is Yes.Vxlan uses the same egress vtep ip transfering either routed or bridged user traffic.Just consider Vxlan a tunnel, and the address of the tunnle endpoint always keeps the same no matter what's travelling in it.

Hope my answers could ease your confusion.

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