CISCO VPN Ports

* UDP port 500
* UDP port 10000 (or any other port number being used for IPSec/UDP)
* IP protocol 50 (ESP)
* TCP port configured for IPSec/TCP
* NAT-T port 4500

The CISCO documentation mentions several other ports, quoting:
* UDP port 500
* UDP port 10000 and 500 (or any other port number being used for IPSec/UDP)
* IP protocol 50 (ESP)
* NAT-T port 4500 UDP