Hi Jeff,
As can be seen in the following allowing PPTP through the PIX:
http://www.cisco.com/en/US/products/hw/vpndevc/ps2030/products_configuration_example09186a0080094a5a.shtml
You can just replace the ports for PPTP to those for IPSec and get going on this:
Ports to allow for IPSec:
UDP port 500, IP protocol 50 (ESP), IP Protocol 51 (AH).
Additionally if they are doing any IPSec/NAT ports then you need to open those aswell, but confirm those with them as it depends on what the terminating device is for it.
Regards,
Aamir
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