After an engineer configures an IPSec tunnel with a Cisco ASA, the Palo Alto Networks...

The Proxy IDs (or Traffic Selectors) define the local and remote subnets that are allowed to communicate over the IPSec tunnel. If the Proxy IDs on the Palo Alto Networks firewall do not match the configuration on the Cisco ASA, the tunnel will fail to establish because the firewalls won't agree on which traffic to encrypt. Ensuring that the Proxy IDs match between the Palo Alto Networks firewall and the Cisco ASA will resolve the issue.