Reference Guide

Virtual Link Trunking (VLT) | 999
VLT and Stacking
Stacking S4810 units cannot be enabled with VLT. If stacking is currently enabled on a unit on which you
want to enable VLT, you must first remove the unit from the existing stack. For information on how to
remove a unit from a stack, see Chapter 46, Stacking, Remove a Unit from an S-Series Stack on page 921.
After the unit has been removed, VLT can be configured on the unit.
VLT and IGMP Snooping
When configuring IGMP Snooping with VLT, you must ensure the configurations on both sides of the
VLT trunk are identical to get the same behavior on both sides of the trunk. When IGMP Snooping is
configured on a VLT node, the dynamically learned groups and multicast router ports are automatically
learned on the VLT peer node.
VLT Port Delayed Restoration
With FTOS Release 8.3.12.0, when a VLT node boots up, if the VLT ports have been previously saved in
the start-up configuration, they will not be immediately enabled. To ensure MAC and ARP entries from the
VLT per node are downloaded to the newly enabled VLT node, the system allows time for the VLT ports
on the new node to be enabled and begin receiving traffic.
The
delay-restore feature waits for all saved configurations to be applied, then starts a configurable timer.
After the timer expires, the VLT ports are enabled one-by-one in a controlled manner. The delay between
bringing up each VLT port-channel is proportional to the number of physical members in the port-channel.
Use the
delay-restore command to change the duration of the configurable timer; the default is 90 seconds.
If IGMP Snooping is enabled, IGMP queries are also sent out on the VLT ports at this time allowing any
receivers to respond to the queries and update the multicast table on the new node.
This delay in bringing up the VLT ports also applies when the VLTi link recovers from a failure that
caused the VLT ports on the secondary VLT peer node to be disabled.