VXLAN Control Plane and Data Plane traffic over Multicast.

Anycast-PIM Control Plane Operation

In order to understand the Control Plane Operation over Multicast, first shut down the NVE Interface on both VTEP Switches.

Once this is done , Multicast group 238.0.0.10 (MG) specific Incoming Interface List (IIL) and Outgoing Interface List (OIL) becomes empty on Multicast RIB of both Spine Switches .

Now lets understand the Multicast process, of forming the PIM tree using PIM Join and PIM Register.

Phase 1: PIM Join:

Now as soon as NVE1 interface on VTEP-101 comes UP, it will trigger PIM join process. VTEP-101 uses PIM join message to inform its willingness to receive Multicast traffic, which will be sent to Multicast group 238.0.0.10.

This PIM Join message will be sent to RP, Each VTEP will have two equal path to both Spine as , both spine shares the Anycast RP address. Here one of the Upstream link will be selected to reverse path forwarding ( RFP) list and in regards to this VTEP-101 will chose link to Spine-11 in to RPF list with outgoing interface E1/1. Source address is VTEP-101 underlay network IP address 192.168.0.101 ( Loopback 0).

Now below capture will show you the PIM join Message captured from Interface E1/1 on VTEP-101.

Phase 2 PIM Register:

In L2BUM Multicast Routing, All VTEP switch will also be source. VTEP-101 will also inform to RP that, It is also source for Multicast group 238.0.0.10 and due to which Leaf-101 will send the PIM register message to MG specific RP. Now PIM register message will also be routed based on Unicast RIB. Now VTEP-101 has two equal cost paths for RP, It will do ECMP hash on both link and select one of the link towards Spine.

Here VTEP-101 select link towards Spine-12 and PIM register Message will use the encapsulation method where Multicast traffic to specific group will be encapsulated by outer IP header and destination IP is set to RP IP address. And Once registration is done, all L2BUM traffic will be sent without encapsulation using multicast group address as destination IP.

Below figure shows PIM register message from VTEP-101 to Anycast RP

Phase 3: PIM Register Stop

Now Spine-12 will instruct the VTEP-101, to stop encapsulating the multicast traffic within PIM register Message. In order to do that , Spine-12 will send the PIM register-stop message , where Spine-12 will use source IP as Anycast-RP IP address and VTEP-101 NVE1 IP address as destination IP address.

Phase 4: Anycast-RP Peer Notification

Now here Spine-11 receives the PIM join message from VTEP-101, and Spine-12 receives the PIM register Message.  In order to complete the registration process , Spine-12 will forward the PIM register message received from VTEP-101 to its Anycast-RP Cluster member that is Spine-11. Spine encapsulates the original PIM Register message with an outer IP header where it uses it’s own Unique Anycast-RP Cluster IP address 192.168.121.12 as source and unique Anycast RP Cluster Ip address 192.168.121.11 of Spine-11 as a destination.

As soon as Spine-11 receives the forwarded PIM , It verifies that the sender is part of the same Anycast-RP Cluster by checking that Source IP address in the outer IP header is also defined as an Anycast-RP Cluster member.