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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.
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 and you enable VLT Multicast Routing, multicast
routes are synced to the other peer for traffic forwarding to ensure minimal traffic loss. If you did not
enable VLT Multicast Routing, traffic loss occurs until the other VLT peer is selected as the DR.
VLT Routing
VLT unicast and multicast routing is supported on the switch.
Layer 2 protocols from the ToR to the server are intra-rack and inter-rack. No spanning tree is required,
but interoperability with spanning trees at the aggregation layer is supported. Communication is active-
active, with no blocked links. MAC tables are synchronized between VLT nodes for bridging and you can
enable IGMP snooping.
Because VLT ports are Layer 2 ports and not IP interfaces, VLT Unicast and VLT Multicast routing
protocols do not operate directly on VLT ports. You must add the VLT ports as a member of one or more
VLANs and assign IP addresses to these VLANs. VLT Unicast and VLT Multicast routing protocols require
VLAN IP interfaces for operation. Protocols such as BGP, ISIS, OSPF, and PIM are compatible with VLT
Unicast Routing and VLT Multicast Routing.
Spanned VLANs
Any VLAN configured on both VLT peer nodes is referred to as a Spanned VLAN. The VLT Interconnect
(VLTi) port is automatically added as a member of the Spanned VLAN. As a result, any adjacent router
connected to at least one VLT node on a Spanned VLAN subnet is directly reachable from both VLT peer
nodes at the routing level.
VLT Unicast Routing
VLT unicast routing locally routes packets destined for the L3 endpoint of the VLT peer. This method
avoids suboptimal routing.
In VLT unicast routing, peer-routing syncs the MAC addresses of both VLT peers and requires two local
DA entries in TCAM. In case a VLT node is down, a timer that allows you to configure the amount of time
needed for peer recovery provides resiliency. You can enable VLT unicast across multiple configurations
using VLT links. You can enable ECMP on VLT nodes using VLT unicast.
VLT unicast routing is supported on both IPv4 and IPv6. To enable VLT unicast routing, both VLT peers
must be in L3 mode. Static route and routing protocols such as RIP, OSPF, ISIS, and BGP are supported.
However, point-to-point configuration is not supported. To enable VLT unicast, VLAN configuration must
be symmetrical on both peers. You cannot configure the same VLAN as Layer 2 on one node and as
Virtual Link Trunking (VLT)
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