Configuring The Tunnel Source - HP ProCurve Secure Router 7203 dl Advanced Management And Configuration Manual

When a packet arrives on the tunnel interface, GRE encapsulates it with a GRE
header. This header includes a field identifying the encapsulated packet's
protocol. GRE next encapsulates the GRE header with another IP header. This
is the delivery header: it directs the packet through the tunnel to the remote
endpoint.
IP
Payload
header
1.1.1.1
Router A
Figure 9-1. GRE Tunneling
The tunnel's source is the source address in the delivery IP header, and the
tunnel's destination is the delivery IP header's destination address. (See
Figure 9-1.)
The IP address for the tunnel interface is the forwarding address for packets
that are to use the GRE tunnel.

Configuring the Tunnel Source

Specify the local endpoint for the tunnel. This address is the tunnel destination
for the remote router's tunnel interface, and the remote router and Internet
service provider (ISP) routers must be able to reach this address. Move to the
tunnel interface configuration mode and enter this command to configure the
tunnel source:
Syntax: tunnel source [<A.B.C.D> | <interface ID>]
Configuring a Tunnel with Generic Routing Encapsulation
GRE Delivery IP
header header
Source:
1.1.1.1
Destination:
2.2.2.2
Internet
GRE tunnel
192.168.10.0/30
Configuring GRE
2.2.2.2
Router B
9-5