The VPN gateway Branch office initiates a VPN connection to the gateway Headquarters. Branch office has a dynamic IP address that was chosen and assigned by the Internet service provider upon dialling in, whereas Headquarters has a fixed, static address. When the connection is set up, Branch office transmits its actual IP address to Headquarters. This is accomplished by a special ICMP packet (alternatively UDP, port 87).
| Entry | Headquarters | Branch_office | |
|---|---|---|---|
| Type of local IP address | static |  |
dynamic |
| Type of remote IP address | dynamic | static | |
| Name of the local device | Headquarters |  |
Branch_office |
| Name of the remote device | Branch_office | Headquarters | |
| Password for the secure transmission of the IP address | confidential |  |
confidential |
| Shared Secret for encryption | secret |  |
secret |
| IP address of the remote device | – | 193.10.10.1 | |
| IP-network address of the remote network | 10.10.2.0 | 10.10.1.0 | |
| Netmask of the remote network | 255.255.255.0 | 255.255.255.0 |
Note: An ISDN line is not necessary for establishing this type of connection.
The dynamic end communicates its IP address encrypted via the Internet
protocol ICMP (or alternatively via UDP).