VLT Nodes as Rendezvous Points for Multicast ResiliencyYou can configure virtual link trunking (VLT) peer nodes as rendezvous points (RPs) in a Protocol Independent Multicast (PIM)domain.PIM uses a VLT node as the RP to distribute multicast traffic to a multicast group. Messages to join the multicast group (Joinmessages) and data are sent towards the RP, so that receivers can discover who the senders are and begin receiving traffic destinedfor the multicast group.To enable an explicit multicast routing table synchronization method for VLT nodes, you can configure VLT nodes as RPs. Multicastrouting needs to identify the incoming interface for each route. The PIM running on both VLT peers enables both the peers to obtaintraffic from the same incoming interface.You can configure a VLT node to be an RP through the ip pim rp-address command in Global Configuration mode. When youconfigure a VLT node as an RP, the (*, G) routes that are synchronized from the VLT peers are ignored and not downloaded to thedevice. 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 multicasttraffic 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 notsupport 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 theroute was learned) and another VLT node selects a VLT VLAN. Such a scenario can cause duplication of packets. ECMP is notsupported 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 RPreboots, it can handle new clients only after it comes back online. Until the RP returns to the active state, the VLT peer forwards thepackets for the already logged-in clients. To enable the VLT peer node to retain the synchronized multicast routes or synchronizedmulticast outgoing interface (OIF) maps after a peer node failure, use the timeout value that you configured through themulticast peer-routing timeout value command. You can configure an optimal time for a VLT node to retain syncedmulticast routes or synced multicast outgoing interface (OIF), after a VLT peer node failure, through the multicast peer-routing-timeout command in VLT DOMAIN mode. Using the bootstrap router (BSR) mechanism, both the VLT nodes in a VLTdomain can be configured as the candidate RP for the same group range. When an RP fails, the VLT peer automatically takes overthe role of the RP. This phenomenon enables resiliency to be achieved by the PIM BSR protocol.Configuring VLAN-Stack over VLTTo configure VLAN-stack over VLT, follow these steps.1. Configure the VLT LAG as VLAN-stack access or trunk mode on both the peers.INTERFACE PORT-CHANNEL modevlan-stack {access | trunk}2. Configure VLAN as VLAN-stack compatible on both the peers.INTERFACE VLAN modevlan-stack compatible3. Add the VLT LAG as a member to the VLAN-stack on both the peers.INTERFACE VLAN mode940 Virtual Link Trunking (VLT)
