VSX switch reboot

After a VSX switch reboots, it has no entries for ARP, MAC, and routes. If downstream VSX LAG ports are activated before all this information is relearned, traffic is dropped. To avoid a traffic drop, VSX LAGs on the rebooted switch stay down until the restoration of LACP, MAC, and ARP databases.

The learning process for the VSX LAGs has two phases:

• Initial sync phase: The LACP states, MAC address table, and ARP table are downloaded from the forwarding switch to the freshly rebooted switch.

• Link-up delay phase: The downloaded entries are installed into the ASIC. Router adjacencies with core nodes and learned upstream routes are also established.

  The link-up delay phase is configurable with the linkup-delay-timer <DELAY-TIMER> command. The default value is 180 seconds. Set the link-up delay timer to the maximum value of 600 seconds for a network with many MAC addresses, a large ARP table, or a large routing table.

When both VSX switches reboot, the link-up delay timer is not used because both switches are trying to relearn the LACP states, MAC address table, and ARP table.

To get upstream router adjacencies established during the link-up delay, the upstream LAGs have to be excluded from the scope of the link-up delay. Run the linkup-delay-timer exclude lag-list <LAG-LIST> for identifying the LAGs for exclusion.

For example, assume that you have a topology similar to the one in Sample VSX solution topology, the upstream LAGs (LAG 101 and LAG 102), would need to be identified by the linkup-delay-timer exclude lag-list <LAG-LIST> for exclusion before a VSX switch reboot.