node to choose a different VLAN or IP route to reach the PIM neighbor. This can result in issues withmulticast route syncing between peers.• Both VLT peers require symmetric Layer 2 and Layer 3 configurations on both VLT peers for anyspanned VLAN.• For optimal performance, configure the VLT VLAN routing metrics to prefer VLT VLAN interfaces overnon-VLT VLAN interfaces.• When using factory default settings on a new switch deployed as a VLT node, packet loss may occurdue to the requirement that all ports must be open.• ECMP is not compatible on VLT nodes using VLT multicast. You must use a single VLAN.Configuring VLT MulticastTo enable and configure VLT multicast, follow these steps.1. Enable VLT on a switch, then configure a VLT domain and enter VLT-domain configuration mode.CONFIGURATION modevlt domain domain-id2. Enable peer-routing.VLT DOMAIN modepeer-routing3. Configure the multicast peer-routing timeout.VLT DOMAIN modemulticast peer-routing—timeout valuevalue: Specify a value (in seconds) from 1 to 1200.4. Configure a PIM-SM compatible VLT node as a designated router (DR). For more information, refer toConfiguring a Designated Router.5. Configure a PIM-enabled external neighboring router as a rendezvous point (RP). For moreinformation, refer to Configuring a Static Rendezvous Point.6. Configure the VLT VLAN routing metrics to prefer VLT VLAN interfaces over non-VLT VLANinterfaces. For more information, refer to Classify Traffic.7. Configure symmetrical Layer 2 and Layer 3 configurations on both VLT peers for any spanned VLAN.Non-VLT ARP SyncARP entries (including ND entries) learned on other ports are synced with the VLT peer to support stationmove scenarios.NOTE: ARP entries learned on non-VLT, non-spanned VLANs are not synced with VLT peers.RSTP ConfigurationRSTP is supported in a VLT domain.Before you configure VLT on peer switches, configure RSTP in the network. RSTP is required for initialloop prevention during the VLT startup phase. You may also use RSTP for loop prevention in the networkoutside of the VLT port channel. For information about how to configure RSTP, Rapid Spanning TreeProtocol (RSTP).Virtual Link Trunking (VLT) 937
