Administrator Guide

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 congured 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 trac 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 congure 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 trac forwarding to ensure minimal trac loss. If you did not enable VLT Multicast Routing, trac 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.
In a single homed setup, inter-VLAN routing to a host connected to the PE in the secondary VLT node does not work if the trac
ingressing VLAN is present only in primary VLT node.
Spanned VLANs
Any VLAN congured 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 congure the amount of time needed for peer recovery provides resiliency. You can enable VLT
unicast across multiple congurations 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 conguration is not supported. To enable
Virtual Link Trunking (VLT)
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