Users Guide

Primary and Secondary VLT Peers
Primary and Secondary VLT Peers are supported on the Aggregator.
To prevent issues when connectivity between peers is lost, you can designate Primary and Secondary
roles for VLT peers . You can elect or configure the Primary Peer. By default, the peer with the lowest
MAC address is selected as the Primary Peer.
If the VLTi link fails, the status of the remote VLT Primary Peer is checked using the backup link. If the
remote VLT Primary Peer is available, the Secondary Peer disables all VLT ports to prevent loops.
If all ports in the VLTi link fail or if the communication between VLTi links fails, VLT checks the backup link
to determine the cause of the failure. If the failed peer can still transmit heartbeat messages, the
Secondary Peer disables all VLT member ports and any Layer 3 interfaces attached to the VLAN
associated with the VLT domain. If heartbeat messages are not received, the Secondary Peer forwards
traffic assumes the role of the Primary Peer. If the original Primary Peer is restored, the VLT peer
reassigned as the Primary Peer retains this role and the other peer must be reassigned as a Secondary
Peer. Peer role changes are reported as SNMP traps.
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 Stacking
You cannot enable stacking 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 remove the unit, you can configure VLT on the unit.
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.
PMUX Mode of the IO Aggregator
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