Virtual Private Networking
148
GRE
The GRE configuration of the SnapGear appliance allows you to build GRE tunnels to
other devices that support the
Generic Routing Encapsulating
protocol. You can build
GRE tunnels to other SnapGear appliances that support GRE, or to other devices such
as Cisco equipment.
GRE tunnels are useful for redistributing IPv6 or broadcast and multicast traffic across a
VPN connection. It is also useful for carrying unsupported protocols such as IPX or
Appletalk between remote IP networks.
Warning
GRE tunnels are not secure unless they are run over another secure protocol. Using a
GRE tunnel that runs over the Internet, it is possible for an attacker to put packets onto
your network. If you want a tunneling mechanism to securely connect to networks, then
you should use IPSec, or tunnel GRE over either IPSec or PPTP tunnels.
An example setup that describes using GRE to bridge a network over an IPSec tunnel is
described in
GRE over IPSec
.
Setting up a GRE tunnel
In this example we will connect two office networks using a GRE tunnel between two
SnapGear appliances. One is located in Brisbane, the other in Slough. The two
networks have the following configuration:
SnapGear appliance in Brisbane
Internet address:
203.23.45.6
LAN address:
192.168.1.1
LAN:
192.168.1.0 / 255.255.255.0
SnapGear appliance in Slough
Internet address:
195.45.67.8
LAN address:
10.1.0.1
LAN:
10.1.0.0 / 255.255.0.0
