ZyXEL Communications Parental Control Gateway HS100/HS100W - Manual (Page 351)

HomeSafe User’s Guide
Triangle Route K-1
Appendix K
Triangle Route
The Ideal Setup
When the firewall is on, your HomeSafeacts as a secure gateway between your LAN and the
Internet. In an ideal network topology, all incoming and outgoing network traffic passes through
the HomeSafeto protect your LAN against attacks.
Diagram K-1 Ideal Setup
The “Triangle Route” Problem
A traffic route is a path for sending or receiving data packets between two Ethernet devices.
Some companies have more than one alternate route to one or more ISPs. If the LAN and ISP(s)
are in the same subnet, the “triangle route” problem may occur. The steps below describe the
“triangle route” problem.
Step 1. A computer on the LAN initiates a connection by sending out a SYN packet to a receiving
server on the WAN.
Step 2. The HomeSafereroutes the SYN packet through Gateway B on the LAN to the WAN.
Step 3. The reply from the WAN goes directly to the computer on the LAN without going through the
HomeSafe.
As a result, the HomeSaferesets the connection, as the connection has not been acknowledged.
Diagram K-2 “Triangle Route” Problem
The “Triangle Route” Solutions
This section presents you two solutions to the “triangle route” problem.
IP Aliasing
IP alias allows you to partition your network into logical sections over the same Ethernet
interface. Your HomeSafesupports up to three logical LAN interfaces with the HomeSafebeing
the gateway for each logical network. By putting your LAN and Gateway B in different subnets,
all returning network traffic must pass through the HomeSafeto your LAN. The following steps
describe such a scenario.