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• For optimal performance, configure the VLT VLAN routing metrics to prefer VLT VLAN interfaces over
non-VLT VLAN interfaces.
• When using factory default settings on a new switch deployed as a VLT node, packet loss may occur
due to the requirement that all ports must be open.
• You can enable ECMP on VLT nodes using VLT unicast; however, ECMP is not compatible on VLT
nodes using VLT multicast. You must use a single VLAN.
Configuring VLT Multicast
To enable and configure VLT multicast, follow these steps.
1. Enable VLT on a switch, then configure a VLT domain and enter VLT-domain configuration mode.
CONFIGURATION mode
vlt domain domain-id
2. Enable peer-routing.
VLT DOMAIN mode
peer-routing
3. Configure the multicast peer-routing timeout.
VLT DOMAIN mode
multicast peer-routing—timeout value
value: Specify a value (in seconds) from 1 to 1200.
4. Configure a PIM-SM compatible VLT node as a designated router (DR). For more information, refer to
Configuring a Designated Router.
5. Configure a PIM-enabled external neighboring router as a rendezvous point (RP). For more
information, refer to
Configuring a Static Rendezvous Point.
6. Configure the VLT VLAN routing metrics to prefer VLT VLAN interfaces over non-VLT VLAN
interfaces. For more information, refer to Classify Traffic.
7. Configure symmetrical Layer 2 and Layer 3 configurations on both VLT peers for any spanned VLAN.
VLT Unicast Routing
VLT unicast locally routes 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. In case a VLT node is down, resiliency is provided by a timer that
allows you to configure the amount of time needed for peer recovery.
VLT unicast also assists in conflict resolution by updating the routing table when a path for an existing
multicast route has been changed. You can enable VLT unicast and multicast routing across multiple
configurations using VLT links. ECMP can be enabled on VLT nodes using VLT unicast; however, ECMP is
not compatible on VLT nodes using VLT multicast. You must use a single VLAN.
VLT unicast is supported on both IPV6 / IPv4 . To enable VLT unicast, 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. The same VLAN cannot be configured as Layer 2 on one node and as Layer 3 on the other
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Virtual Link Trunking (VLT)