Site-to-Site IPSec VPN between Palo Alto Networks Firewall and Cisco Router is Unstable or Intermittent

Symptoms

Site-to-Site IPSec VPN has been configured between a Palo Alto Networks firewall and a Cisco router. However, the VPN is unstable or intermittent.

Cause

The issue may be due to a Dead Peer Detection (DPD) configuration mismatch.

Resolution

Check and modify the Palo Alto Networks firewall and Cisco router to have the same DPD configuration.

On the Palo Alto Networks firewall, go to Network > Network Profiles > IKE Gateways as follows:

Confirm that the same configuration is made on the Cisco router:

owner: jlunario