ICL down event is triggered on the other VLT node, which in turn starts the proxy ARP application. The VLT node, where the ICL link isdeleted, flushes the peer IP addresses and does not perform proxy ARP for the additional LAG hashed ARP requests.VLT Nodes as Rendezvous Points for MulticastResiliencyYou can configure 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 (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 multicastgroup.To enable an explicit multicast routing table synchronization method for VLT nodes, you can configure VLT nodes as RPs. Multicast routingneeds to identify the incoming interface for each route. The PIM running on both VLT peers enables both the peers to obtain traffic fromthe 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 configurea 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 areconsidered valid and are downloaded to the device. Only (S, G) routes are used to forward the multicast traffic from the source to thereceiver.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 RPfunctionality.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 waslearned) and another VLT node selects a VLT VLAN. Such a scenario can cause duplication of packets. ECMP is not supported when youconfigure 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 synchronized multicastoutgoing 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 syncedmulticast outgoing interface (OIF), after a VLT peer node failure, using the multicast peer-routing-timeout command in VLTDOMAIN mode. Using the bootstrap router (BSR) mechanism, you can configure both the VLT nodes in a VLT domain as the candidate RPfor the same group range. When an RP fails, the VLT peer automatically takes over the role of the RP. This phenomenon enables resiliencyby 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.Virtual Link Trunking (VLT) 915
