Addendum
Optimizing Traffic Disruption Over LAG Interfaces On IOA
Switches in VLT Mode
When an Aggregator operates in VLT mode, the VLT LAG configurations are saved in nonvolatile storage
(NVS) when you enter the write memory command. This method of saving the VLT settings in NVS and
restoring the saved settings when the Aggregator restarts reduces the disruption of traffic that is handled
during the restart of the primary and secondary VLT peer nodes. By restoring the settings saved in NVS,
the VLT ports come up in a quicker way on the primary VLT node. On the secondary VLT peer node, the
delay in restoration of the VLT LAG parameters is reduced (90 seconds by default) before it becomes
operationally up. This makes sure that the configuration settings of the primary VLT node are
synchronized with the secondary VLT peer node before the secondary VLT mode becomes operational.
In VLT mode of the Aggregator, the LAG bundle is automatically established when the LACP PDU is
received on the port and LAG configurations are not saved. When the VLT LAG parameters are not saved
in NVS, this behavior impacts the VLT port from being brought up in a faster, effective manner during the
VLT node restart because of the switchover of traffic from the primary to the secondary VLT peer node
occurring before the restarted peer node is synchronized with the other peer node.
The VLT domain details, such as the domain ID, the port-channel number that functions as the VLT
interconnect link, the default MAC address of the domain, and the unique unit ID of each peer in the VLT
domain, are stored in NVS. Also, the port-channel member interface details and the VLT LAG
configuration are stored. The traffic outage is less than 200 millisconds during the restart or switchover of
the VLT peer nodes from primary to secondary.
Preserving LAG and Port Channel Settings in Nonvolatile
Storage
You can now use the write memory command on an I/O Aggregator that operates in standalone and
stacking modes, which saves the running configuration to the startup configuration to be preserved
across reboots of the device, to save the LAG port channel configuration parameters. All of the statically
configured port channels (LAG 128) and automatically-configured internal LAGs are saved. This behavior
enables the port channels to be brought up in a faster way because the interface attributes that are
configured are available in the system database during the booting of the device. With the reduction in
time for the port channels to become active after the switch is booted, the loss in the number of packets
that are serviced by these interfaces is minimized.
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Link Aggregation Groups (LAGs)