How to get the Cisco VPN client to work through the ISA Server

Question #834

How in the world do I get the Cisco VPN client to work through the ISA Server?


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The basic setup is: 1. Create two protocol definitions:
– UDP Port 500 Send Receive : this is for the IKE protocol (key negotiation).
– UDP Port XXXX Send Receive : this is for the UDP encapsulated ESP packets.

1. The administrator of the VPN gateway should be able to tell you the exact portnumber to use.
2. Next, create a protocol rule who allows those two created protocols.
3. One thing you must keep in mind is that the client must be a SecureNAT client and that the firewall client must be disabled when setting up the VPN connection. Also, when certificates are involved disable filtering of IP fragments on ISA.
BTW — in general, any IPSec implementation who supports NAT Traversal or UDP encapsulated ESP should work from behind ISA. Many thanks for Stefaan Pouselle for this valuable information!

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