Reference Guide

PIM-Sparse Mode Support on VLT
The designated router functionality of the PIM Sparse-Mode multicast protocol is supported on VLT peer switches for multicast
sources and receivers that are connected to VLT ports.
VLT peer switches can act as a last-hop router for IGMP receivers and as a first-hop router for multicast sources.
Figure 128. 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.
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Virtual Link Trunking (VLT)