Sort of depends what VPN hardware you're using.
The standard IPsec ports are IP protocol 50 (for ESP) and UDP/500 (for ISAKMP). If you're doing NAT-T then it uses UDP/4500. If you're using AH then it uses IP protocol 51.
If you're doing the Cisco Proprietary IPSec encapsulation on the VPN3000's, then by default it uses either TCP port 10000 or UDP port 10000, but you can change the port number to whatever you like.
