Users Guide

vlt domain domain-id
2 Enable peer-routing.
VLT DOMAIN mode
peer-routing
3 Congure the peer-routing timeout.
VLT DOMAIN mode
peer-routing—timeout value
value: Specify a value (in seconds) from 1 to 65535. The default value is innity (without conguring the timeout).
VLT Multicast Routing
VLT multicast routing provides resiliency to multicast routed trac during the multicast routing protocol convergence period after a VLT link
or VLT peer fails using the least intrusive method (PIM) and does not alter current protocol behavior.
Unlike VLT unicast routing, a normal multicast routing protocol does not exchange multicast routes between VLT peers. When you enable
VLT multicast routing, the multicast routing table is synced between the VLT peers. Only multicast routes congured with a Spanned VLAN
IP as their IIF are synced between VLT peers. For multicast routes with a Spanned VLAN IIF, only OIFs congured with a Spanned VLAN IP
interface are synced between VLT peers.
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.
Virtual Link Trunking (VLT)
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