D-Link NetDefend DFL-210 User Manual page 99

3.3.5. GRE Tunnels
The diagram above shows a typical GRE scenario, where two NetDefend Firewalls A and B must
communicate with each other through the intervening internal network 172.16.0.0/16.
Any traffic passing between A and B is tunneled through the intervening network using a GRE
tunnel and since the network is internal and not public there is no need for encryption.
Setup for NetDefend Firewall "A"
Assuming that the network 192.168.10.0/24 is lannet on the lan interface, the steps for setting up
NetDefendOS on A are:
1. In the address book set up the following IP objects:
• remote_net_B: 192.168.11.0/24
• remote_gw: 172.16.1.1
• ip_GRE: 192.168.0.1
2. Create a GRE Tunnel object called GRE_to_B with the following parameters:
• IP Address: ip_GRE
• Remote Network: remote_net_B
• Remote Endpoint: remote_gw
• Use Session Key: 1
• Additional Encapulation Checksum: Enabled
3. Define a route in the main routing table which routes all traffic to remote_net_B on the
GRE_to_B GRE interface. This is not necessary if the option Add route for remote network
is enabled in the Advanced tab, since this will add the route automatically.
4. Create the following rules in the IP rule set that allow traffic to pass through the tunnel:
Name
To_B
From_B
Action Src Int
Allow lan
Allow GRE_to_B
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Src Net Dest Int
lannet GRE_to_B
remote_net_B lan
Chapter 3. Fundamentals
Dest Net Service
remote_net_B All
lannet All