• Configure any ports at the edge of the spanning tree’s operating domain as edge ports, which are directly connected to end stations orserver racks. Disable RSTP on ports connected directly to Layer 3-only routers not running STP or configure them as edge ports.• Ensure that the primary VLT node is the root bridge and the secondary VLT peer node has the second-best bridge ID in the network. Ifthe primary VLT peer node fails, the secondary VLT peer node becomes the root bridge, avoiding problems with spanning tree portstate 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 toother Layer 2 switches, spanning tree topology changes are still detected after VLT node recovery. To avoid this scenario, ensure thatyou configure any non-VLT ports as edge ports or disable RSTP.VLT Bandwidth MonitoringWhen bandwidth usage of the VLTi (ICL) exceeds 80%, a syslog error message (shown in the following message) and an SNMP trap aregenerated.%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 followingmessage) 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 statusVLT and StackingYou cannot enable stacking on the units with VLT.If you enable stacking on a unit on which you want to enable VLT, you must first remove the unit from the existing stack. After you removethe unit, you can configure VLT on the unit.VLT and IGMP SnoopingWhen configuring IGMP Snooping with VLT, ensure the configurations on both sides of the VLT trunk are identical to get the samebehavior 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 onthe VLT peer node.VLT IPv6The following features have been enhanced to support IPv6:• VLT Sync — Entries learned on the VLT interface are synced on both VLT peers.• Non-VLT Sync — Entries learned on non-VLT interfaces are synced on both VLT peers.• Tunneling — Control information is associated with tunnel traffic so that the appropriate VLT peer can mirror the ingress port as theVLT interface rather than pointing to the VLT peer’s VLTi link.• Statistics and Counters — Statistical and counter information displays IPv6 information when applicable.• Heartbeat — You can configure an IPv4 or IPv6 address as a backup link destination. You cannot use an IPv4 and an IPv6 addresssimultaneously.Virtual Link Trunking (VLT) 929
