Please make sure NAT-traversal is enabled on both side firewalls to accept IKE on port 4500. During IKE negotiation, 3rd message onwards, port will flip to UDP 4500.
Traditionally, IPSec does not work when traversing across a device doing NAT. To circumvent this problem, NAT-T or NAT Traversal was developed. NAT-T is an IKE phase 1 algorithm that is used when trying to establish a VPN between two gateways devices where a NAT device exists in front of one of the devices.
I dont' have any control over the remote site, but if I am able to send 500 ike traffice out into the internet and am not seeing 4500 traffic traying to come in not sure how nat-t would affect it
I have a vendor that creates a vpn tunnel using a fortinet device behind our PA 3020. The device initiates the tunnel,the ike 500 traffic I am seeing passing throught the PA into the internet, Then I would assume a device on the vendors side exchanges SA's with the 500 traffic should say okay and builds the ipsec/udp tunnel using port 4500. I am trying to confirm that we are making in past the pa firewall into the internet and not blocking a response from the vendor
Ok, then nothing has to be done on the PAN firewall apart from a general security policy etc.
You can check the real time session in the CLI by using 'show session all filter source IP_ADD_OF_THE_TESTING_PC destination IP_ADD_OF_THE_DESTINATION'.
> If there is a session exist for the same traffic, then please apply CLI command PAN> show session id XYZ >>>>>>>> to get detailed information about that session, i.e NAT rule, security rule, ingress/egress interface etc.
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