Users Guide

that originates from the source that is connected to the VLT ports to reach the PIM router which has
downstream neighbors.
The VLT peer nodes can also act as normal PIM routers on Layer 3 ports and on VLANs that do not have any
VLT port members. In addition to being first-hop or last -hop routers, the peer node can also act as an
intermediate router.
To route traffic to and from the multicast source and receiver that are connected to VLT ports, enable PIM-
Sparse mode on the VLANs to which the VLT ports belong using the ip pim sparse-mode command. If you
configure IGMP snooping on these VLANs, the VLTi must be configured as a static multicast router port on
both VLT peers.
Each VLT peer runs its own PIM protocol independently of other VLT peers. To ensure the PIM protocol states
or multicast routing information base (MRIB) on the VLT peers are synced, if the incoming interface (IIF) and
outgoing interface (OIF) are Spanned, the multicast route table is synced between the VLT peers.
To verify the PIM neighbors on the VLT VLAN and on the multicast port, use the show ip pim neighbor,
show ip igmp snooping mrouter, and show running config commands.
You cannot configure VLT peer nodes as rendezvous points, but you can connect PIM routers to VLT ports.
If the VLT node elected as the designated router fails, traffic loss will occur until another VLT node is elected
the designated router.
RSTP Configuration
RSTP is supported in a VLT domain.
Before you configure VLT on peer switches, configure RSTP in the network. RSTP is required for initial loop
prevention during the VLT startup phase. You may also use RSTP for loop prevention in the network outside
of the VLT port channel. For information about how to configure RSTP, Rapid Spanning Tree Protocol (RSTP).
Run RSTP on both VLT peer switches. The primary VLT peer controls the RSTP states, such as forwarding and
blocking, on both the primary and secondary peers. Dell Networking recommends configuring the primary
VLT peer as the RSTP primary root device and configuring the secondary VLT peer as the RSTP secondary
root device.
BPDUs use the MAC address of the primary VLT peer as the RSTP bridge ID in the designated bridge ID field.
The primary VLT peer sends these BPDUs on VLT interfaces connected to access devices. The MAC address
for a VLT domain is automatically selected on the peer switches when you create the domain (refer to
Enabling VLT and Creating a VLT Domain).
Configure both ends of the VLT interconnect trunk with identical RSTP configurations. When you enable VLT,
the show spanning-tree rstp brief command output displays VLT information (refer to
Verifying a VLT Configuration).
Virtual Link Trunking (VLT) 1136