Below are steps to setup IPSEC Tunnel Between Palo Alto Firewalls.
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1.Make sure you have connectivity between Peer.
2.Create IKE Crypto.
3. Create IPSEC Crypto.
4.Create IKE Gateway.
5.Create tunnel interface give it IP address and zone.
6.Create IPSEC Tunnel.
7. Create Static route pointing to tunnel interface ( Peer side network route it to tunnel interface).
8.Security policy to allow ike and ipsec.
9.Security policy to allow interesting traffic .
10. Run Ping test between 192.168.10.100 and 192.168.20.100.