Reference Guide

922 | Virtual Link Trunking (VLT)
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When the bandwidth usage drops below the 80% threshold, the system generates another syslog message
(Message 2) and an SNMP trap.
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.
Message 2 Excessive VLTi Bandwidth Usage Drops Below Threshold Value Error
%STKUNIT0-M:CP %VLTMGR-6-VLT-LAG-ICL: Overall Bandwidth utilization of VLT-ICL-LAG (port-channel 25)
reaches below threshold. Bandwidth usage (74% )VLT show remote port channel status