Addendum

• L3 routing is enabled on any VLAN with an admin state of up.
NOTE: If the CAM is full, do not enable peer-routing.
Configuring VLT Unicast
To enable and configure VLT unicast, 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 peer-routing timeout.
VLT DOMAIN mode
peer-routing—timeout value
value: Specify a value (in seconds) from 1 to 65535.
VLT Multicast Routing
VLT multicast routing is supported on the Z9000 S4810 S4820T platform.
VLT Multicast Routing provides resiliency to multicast routed traffic 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 configured with a Spanned VLAN IP as their IIF are synced
between VLT peers. For multicast routes with a Spanned VLAN IIF, only OIFs configured 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 traffic hashes to the VLT peer, the traffic
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 traffic can directly route traffic to all
downstream routers connected on VLT ports.
• Optimal VLTi forwarding — Only one copy of the incoming multicast traffic 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 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.
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Virtual Link Trunking (VLT)