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Important Points to Remember
• You cannot configure a VLT node as a rendezvous point (RP), but any PIM-SM compatible VLT node
can serve as a designated router (DR).
• You can only use one spanned VLAN from a PIM-enabled VLT node to an external neighboring PIM
router.
• If you connect multiple spanned VLANs to a PIM neighbor, or if both spanned and non-spanned
VLANs can access the PIM neighbor, ECMP can cause the PIM protocol running on each VLT peer
node to choose a different VLAN or IP route to reach the PIM neighbor. This can result in issues with
multicast route syncing between peers.
• Both VLT peers require symmetric Layer 2 and Layer 3 configurations on both VLT peers for any
spanned VLAN.
• 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.
• 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.
Non-VLT ARP Sync
Synchronization for non-ARP routing table entries is supported on the switch.
ARP entries (including ND entries) learned on other ports are synced with the VLT peer to support station
move scenarios.
NOTE: ARP entries learned on non-VLT, non-spanned VLANs are not synced with VLT peers.
Virtual Link Trunking (VLT)
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