Keepalive is a layer 3 interface that is used to exchange heartbeats between VSX peer switches. The heartbeats are exchanged by using the User Datagram Protocol (UDP) and port 7678 (default).

Configure each VSX peer switch with a keepalive connection to the other VSX peer switch. This connection is established over a routed network (IPv4 currently) and does not have to be a dedicated peer-to-peer link unlike ISL. Keepalive packets are UDP-based.

The VSX peer switches should have layer 3 reachability for keepalive interfaces through directly connected interfaces or routed through the upstream layer 3 network. Source of keepalive interfaces can be a layer 3 interface (router port), a loopback interface, or a Switch Virtual Interface (SVI). An SVI is a logical layer 3 interface configured per VLAN (one-to-one mapping) that performs all layer 3 processing for packets to or from all switch ports associated with that VLAN.


With respect to the keepalive path, it is highly recommended to separate keepalive traffic from the ISL link.

Use a dedicated layer 3 link.

Keepalive packets can be sourced from the supported layer 3 interface; however, the packet must not be transported over the ISL.