Configuring a GRE Tunnel Using Cisco
IOS Commands
To configure GRE using Cisco IOS commands, you must first configure a
logical tunnel interface. GRE commands are then given under that interface.
You must specify a source and destination for the tunnel; the source is a
local outgoing interface. You may also give the tunnel interface an IP address
and specify the Tunnel mode. GRE is the default mode.
The following example shows a tunnel interface configured for GRE. The
mode command is shown only as a reference—because it is the default, it
would not normally appear in the configuration:
interface Tunnel1
ip address 172.16.5.2 255.255.255.0
tunnel source Serial0/0
tunnel destination 10.1.1.1
tunnel mode gre ip