HP ProCurve Secure Router 7203 dl Advanced Management And Configuration Manual page 906

Using the Web Browser Interface for Advanced Configuration Tasks
Setting Up Generic Routing Encapsulation (GRE) Tunnels
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5. Enter the tunnel's source address in the Tunnel Source section. The
tunnel's source is the endpoint that the peer knows how to reach, often
the router's public IP address. You can configure the source in one of two
ways:
a. You can select Address and enter the address in the fields to the right.
b. Often, however, you should select an interface to use as the tunnel
endpoint. For example, you can select a loopback interface or the
WAN interface that connects to the Internet. The tunnel source will
then remain valid even if your public IP address changes.
Click the Interface circle and select an interface from the pull-down
menu. This interface's IP address will be the source address in tun-
neled packets' delivery IP headers.
6. Enter the IP address for the remote endpoint of the tunnel in the Desti-
nation Address fields. You should enter the public address for the remote
endpoint.
7. You configure optional settings in the GRE Settings section.
Figure 14-82.Configuring Tunnel GRE Settings
8. If you want to enable the router to use the checksum function, select the
Tunnel Checksumming box. Checksums protect against garbled data;
however, both ends of the tunnel must implement the checksum function
in order for it to have an effect.