Users Guide

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 can congure virtual link trunking (VLT) peer nodes as rendezvous points (RPs) in a Protocol Independent Multicast (PIM) domain.
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 Routing refers to the ability to run a dynamic routing protocol within a single VLT domain or between VLT domains (mVLT). In a single
VLT domain, VLT routing allows routing adjacencies to be formed across the VLTi link. In eVLT, routing adjacencies are formed across the
port-channel that connects the two VLT domains.
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.
Layer 2 protocols from the ToR devices to the server are intra-rack and inter-rack. Although no spanning tree is required, interoperability
with spanning trees at the aggregation layer is supported to prevent switching loops from forming due to any incorrect conguration. .
Communication between devices is active-active, with no blocked links. MAC tables are synchronized between VLT nodes for bridging and
you can enable IGMP snooping.
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 is a type of VLT peer routing that locally routes unicast packets destined for the L3 endpoint of the VLT peer. This
method avoids sub-optimal routing. Peer-routing syncs the MAC addresses of both VLT peers and requires two local DA entries in TCAM. If
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
VLT unicast, the VLAN conguration must be symmetrical on both peers. You cannot congure the same VLAN as Layer 2 on one node
and as Layer 3 on the other node. Conguration mismatches are logged in the syslog and display in the show vlt mismatch command
output.
If you enable VLT unicast routing, the following actions occur:
• L3 routing is enabled on any new IP address / IPv6 address congured for a VLAN interface that is up.
• L3 routing is enabled on any VLAN with an admin state of up.
NOTE
: If the CAM is full, do not enable peer-routing.
884 Virtual Link Trunking (VLT)