Dell EMC Configuration Guide for the S3100 Series 9.14.2.4

PIM uses a VLT node as the RP to distribute multicast traffic to a multicast group. Messages to join the multicast group (Join messages) and data are sent towards the RP, so that receivers can discover who the senders are and begin receiving traffic destined for the multicast group.

To enable an explicit multicast routing table synchronization method for VLT nodes, you can configure VLT nodes as RPs. Multicast routing needs to identify the incoming interface for each route. The PIM running on both VLT peers enables both the peers to obtain traffic from the same incoming interface.

You can configure a VLT node to be an RP using the ip pim rp-address command in Global Configuration mode. When you configure a VLT node as an RP, the (*, G) routes that are synchronized from the VLT peers are ignored and not downloaded to the device. For the (S, G) routes that are synchronized from the VLT peer, after the RP starts receiving multicast traffic via these routes, these (S, G) routes are considered valid and are downloaded to the device. Only (S, G) routes are used to forward the multicast traffic from the source to the receiver.

You can configure VLT nodes, which function as RP, as Multicast source discovery protocol (MSDP) peers in different domains. However, you cannot configure the VLT peers as MSDP peers in the same VLT domain. In such instances, the VLT peer does not support the RP functionality.

If the same source or RP can be accessed over both a VLT and a non-VLT VLAN, configure better metrics for the VLT VLANs. Otherwise, it is possible that one VLT node chooses a non-VLT VLAN (if the path through the VLT VLAN was not available when the route was learned) and another VLT node selects a VLT VLAN. Such a scenario can cause duplication of packets. ECMP is not supported when you configure VLT nodes as RPs.

Backup RP is not supported if the VLT peer that functions as the RP is statically configured. With static RP configuration, if the RP reboots, it can handle new clients only after it comes back online. Until the RP returns to the active state, the VLT peer forwards the packets for the already logged-in clients. To enable the VLT peer node to retain the synchronized multicast routes or synchronized multicast outgoing interface (OIF) maps after a peer node failure, use the timeout value that you configured using the multicast peer-routing timeout value command. You can configure an optimal time for a VLT node to retain synced multicast routes or synced multicast outgoing interface (OIF), after a VLT peer node failure, using the multicast peer-routing-timeout command in VLT DOMAIN mode. Using the bootstrap router (BSR) mechanism, you can configure both the VLT nodes in a VLT domain as the candidate RP for the same group range. When an RP fails, the VLT peer automatically takes over the role of the RP. This phenomenon enables resiliency by the PIM BSR protocol.