VXLAN Handling BUM Traffic

In VXLAN networks, BUM (Broadcast, Unknown unicast, and Multicast) traffic can be managed by the underlay transport mechanisms employed. There are two primary methods of doing this.

Multicast Mode

This enables multicast on the NVE interfaces by using the mcast-group command. This results in a multicast group being assigned per VXLAN VNI. When a VTEP receives BUM traffic, it encapsulates it into a VXLAN packet and sends it to the destination multicast group. All VTEPs listening to that group receive and process the traffic.

Static ingress replication (Headend Replication)

This approach replaces the need for a multicast group by manually configuring peer IP addresses on each participating Leaf switch. Configuration involves executing the ingress-replication protocol static and specifying peer IPs using the peer-ip 2.2.2.2. This is less scalable because a peering must be established between all VTEPs that share the same VNI. It is also inefficient because the sender must generate multiple copies of the same frame to send to all associated VTEPs.

Another method that does not eliminate the need for BUM traffic but helps reduce it is worth mentioning here. This is the use of an EVPN control plane. Using EVPN VXLAN BUM suppression techniques like ARP suppression, it helps to reduce unnecessary flooding. The EVPN control plane learns MAC addresses and distributes them over MP-BGP reducing unknown unicast flooding. When employed, you still must configure either multicast mode or static ingress replication to deal with the rest of the BUM traffic, but there is a significant reduction.

https://networklessons.com/vxlan/vxlan-static-ingress-replication

https://networklessons.com/vxlan/vxlan-flood-and-learn-multicast-data-plane

https://networklessons.com/vxlan/vxlan-mp-bgp-evpn-l2-vni

https://networklessons.com/vxlan/mp-bgp-evpn-vxlan-arp-suppression

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