Administrator Guide

the root bridge, avoiding problems with spanning tree port state changes that occur when a VLT node
fails or recovers.
• Even with this configuration, if the node has non-VLT ports using RSTP that you did not configure as
edge ports and are connected to other Layer 2 switches, spanning tree topology changes are still
detected after VLT node recovery. To avoid this scenario, ensure that you configure any non-VLT ports
as edge ports or disable RSTP.
VLT Bandwidth Monitoring
When bandwidth usage of the VLTi (ICL) exceeds 80%, a syslog error message (shown in the following
message) and an SNMP trap are generated.
%STKUNIT0-M:CP %VLTMGR-6-VLT-LAG-ICL: Overall Bandwidth utilization of VLT-ICL-LAG
(port-channel 25)
crosses threshold. Bandwidth usage (80 )
When the bandwidth usage drops below the 80% threshold, the system generates another syslog message
(shown in the following message) and an SNMP trap.
%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
VLT and IGMP Snooping
When configuring IGMP Snooping with VLT, ensure the configurations on both sides of the VLT trunk are
identical to get the same behavior on both sides of the trunk.
When you configure IGMP snooping 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 the Dell Networking OS version 8.3.12.0, when a VLT node boots up, if the VLT ports have been
previously saved in the start-up configuration, they are not 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.
The default is 90 seconds.
To change the duration of the configurable timer, use the delay-restore command.
If you enable IGMP snooping, 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.
Virtual Link Trunking (VLT) 959