All software on the computer is given a port number. VPN Port number for the VPN service are different dipendent on the software and the protocols.

-PPTP encapsulates packets using GRE- Generic routing protocol which uses IP port 47, The IANA list 1723 as the port for VPN. A common mistake in configuring firewalls for use with PPTP is to open port 1723 and close IP port 47. This allows connections to be established but denies the actual data from passing through the tunnel to the machine. Some software utilities verify if both the ports are open for GRE in PPTP to be used.

-L2TP protocol is assigned 115 as its port number.

-IPSec VPN ports assignments for uses of Encapsulation Security payload (protocol 50) and Authentication Header (protocol 51). Port 88 for Kerberos authentication in TCP/UDP and port 500 for Internet Security Association and Key Management Protocol in TCP/UDP.

-SSL VPN for secure HTTP application uses port 443.

-MPLS-in IP uses port 137

-For the systems that use VPN hardware normally port 500,4500,10000 &smp 10001 are used. One for outgoing traffic and the other for incoming traffic.

Some software's make facility to configure them properly, sometimes you may not be able to configure them properly, for example Microsoft VPN port. When VPN hardware is used for a client the process is easy like that for a Cisco VPN port. For a LAN and big networks the network administrator then has to set privileges and configure the firewall as well. This process is necessary for proper security.