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Chapter 13 Firewall
NBG-460N User’s Guide
181
You can have the NBG-460N permit the use of asymmetrical route topology on the
network (not reset the connection).
Allowing asymmetrical routes may let traffic from the WAN go directly to the LAN
without passing through the NBG-460N. A better solution is to use IP alias to put
the NBG-460N and the backup gateway on separate subnets.
13.3.3 Triangle Routes and IP Alias
You can use IP alias instead of allowing triangle routes. IP Alias allow you to
partition your network into logical sections over the same interface.
By putting your LAN and Gateway A in different subnets, all returning network
traffic must pass through the NBG-460N to your LAN. The following steps describe
such a scenario.
1 A computer on the LAN initiates a connection by sending a SYN packet to a
receiving server on the WAN.
2 The NBG-460N reroutes the packet to Gateway A, which is in Subnet 2.
3 The reply from the WAN goes to the NBG-460N.
4 The NBG-460N then sends it to the computer on the LAN in Subnet 1.
Figure 122 Using IP Alias to Solve the Triangle Route Problem