Dell S4048–ON Configuration Manual page 990

Figure 140. PIM-Sparse Mode Support on VLT
On each VLAN where the VLT peer nodes act as the first hop or last hop routers, one of the VLT peer nodes is elected as the PIM
designated router. If you configured IGMP snooping along with PIM on the VLT VLANs, you must configure VLTi as the static multicast
router port on both VLT peer switches. This ensures that for first hop routers, the packets from the source are redirected to the designated
router (DR) if they are incorrectly hashed. In addition to being first-hop or last -hop routers, the peer node can also act as an intermediate
router.
On a VLT-enabled PIM router, if any PIM neighbor is reachable through a Spanned Layer 3 (L3) VLAN interface, this must be the only PIM-
enabled interface to reach that neighbor. A Spanned L3 VLAN is any L3 VLAN configured on both peers in a VLT domain. This does not
apply to server-side L2 VLT ports because they do not connect to any PIM routers. These VLT ports can be members of multiple PIM-
enabled L3 VLANs for compatibility with IGMP.
To route traffic to and from the multicast source and receiver, enable PIM on the L3 side connected to the PIM router using the ip pim
sparse-mode command.
990 Virtual Link Trunking (VLT)