Periodic synchronization

Each VSX node synchronizes every second the following with its VSX peer through ISLP:
  • Learned MAC addresses

  • LACP states

  • STP states

In a VSX scenario if all traffic from core to access flows through one switch only, the other device will also learn about ARP/ND from its VSX peer. There is no functional impact to the normal datapath based learning. VSX split and the rejoin scenario, such as periodic synchronization, resumes after the bulk synchronization.

The IVRL induced neighbor entries are not synced either through the initial ARP synchronization or periodic synchronization. The local IVRL will induce the learning on each side triggered by either a local data-path ARP learned or the ongoing sync based-ARP learned in the source VRF.

IMPORTANT: If you enter one or more of the following commands on one VSX switch but not on the other VSX switch or any configuration is incorrect on one switch , the ARP entries on both switches will become unsynchronized:
  • interface vlan

  • shutdown for a VLAN

  • no shutdown for a VLAN

If you run into this situation, correct the configuration and run the clear arp command, which clears the ARP entries on both VSX nodes. After you run the clear arp command, the ARP entries are synchronized on both switches.

The following image shows how periodic synchronization synchronizes LACP states, MAC, ARP/ND, and MSTP. The image references the VSX synchronization between aggregate 1 (the primary VSX switch) and aggregate 2 (the secondary VSX switch).

Periodic synchronization