Users Guide

The advantages of syncing the multicast routes between VLT peers are:
• VLT resiliency — After a VLT link or peer failure, if the trac hashes to the VLT peer, the trac continues to be routed using multicast
until the PIM protocol detects the failure and adjusts the multicast distribution tree.
• Optimal routing — The VLT peer that receives the incoming trac can directly route trac to all downstream routers connected on
VLT ports.
• Optimal VLTi forwarding — Only one copy of the incoming multicast trac is sent on the VLTi for routing or forwarding to any orphan
ports, rather than forwarding all the routed copies.
Important Points to Remember
• 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 dierent 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 congurations on both VLT peers for any spanned VLAN.
• For optimal performance, congure 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.
Conguring VLT Multicast
To enable and congure VLT multicast, follow these steps.
1 Enable VLT on a switch, then congure a VLT domain and enter VLT-domain conguration mode.
CONFIGURATION mode
vlt domain domain-id
2 Enable peer-routing.
VLT DOMAIN mode
peer-routing
3 Congure the multicast peer-routing timeout.
VLT DOMAIN mode
multicast peer-routing—timeout value
value: Specify a value (in seconds) from 1 to 1200.
4 Congure a PIM-SM compatible VLT node as a designated router (DR). For more information, refer to Conguring a Designated
Router
.
5 Congure a PIM-enabled external neighboring router as a rendezvous point (RP). For more information, refer to Conguring a Static
Rendezvous Point.
6 Congure the VLT VLAN routing metrics to prefer VLT VLAN interfaces over non-VLT VLAN interfaces. For more information, refer to
Classify Trac.
7 Congure symmetrical Layer 2 and Layer 3 congurations on both VLT peers for any spanned VLAN.
Non-VLT ARP Sync
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.
892 Virtual Link Trunking (VLT)