BGP-EVPN Traffic Components

BGP-EVPN Traffic Components

In this Topic we will learn about how traffic flows in VXLAN.

Multidestination Traffic:

Multicast, broadcast and unknown unicast traffic are said be multidestination traffic. (BUM). There are two different methods through which VXLAN handles multidestination traffic.

• Unicast mode ( Ingress replication or head-end-replication)
• Multicast mode.

Unicast mode:  

In unicast mode, BUM packets are replicated by VTEP on which that receives that packet and is sent to all neighboring VTEP that are part of same VNI. If there are N VTEP which has membership to given VNI than a VTEP has to generate the N-1 copies of  packet and send to each one of them with Destination IP is set to each VTEP IP address which has that VNI membership .

In  the fig : Host A (192.168.1.11) connected to VTEP V1 sends an ARP request to resolve the IP-to-MAC for Host B (192.168.1.13) which is connected to VTEP V3. Both the hosts belong to the same subnet 192.168.1.0/24 and VNI is 20001. To handle this BUM packet,  VTEP V1 sends out two unicast packets containing this ARP request payload destined to VTEP V3  and VTEP 2 because these VTEPs  have membership of VNI 20001. But in VTEP 2, no host is connected only on VTEP 2, VNI membership is configured.

Where VTEP will discard that ARP request as it don’t have any active host connected to that subnet.

There are two ways to configure unicast mode.

Static mode:

VNI membership with ingress replication is configured statically on each VTEP .

Dynamic Mode :

Ingress Replication configuration via BGP EVPN method.

In this mode , BGP EVPN control protocol use Route type 3 messages to distribute VTEP and VNI membership information.

Multicast mode: