Periodic synchronization

Each VSX node synchronizes every second the following with its VSX peer through ISLP:

Learned MAC addresses
LACP states
MSTP 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 spit 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, the ARP entries on both switches will become unsynchronized:

clear arp
interface vlan
shutdown for a VLAN
no shutdown for a VLAN

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