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I've a Cisco ASA 5510 with transparent mode, and I'm going to setup a IPsec VPN(Openswan) in a internal linux server(with Public IP). This server has 2 NIC, 1 public IP, and 1 internal IP.

I've opened port 500 and 4500 in the Cisco firewall, however, the vpn still doesn't work.

Do I need to change any setting in the Cisco firewall?


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up vote 2 down vote accepted

UDP port 500 is only used for the initial handshake. If you're running IPsec in transport mode, the actual secured traffic is ESP-encapsulated. So you will also need to let all ESP-encapsulated packets through. This is not TCP or UDP traffic, but a different protocol on top of IP.

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