Chapter 6 Bridge Screens; Bridge; Bridge Loop; Figure 39 Bridge Loop: Bridge Connected To Wired Lan - ZyXEL Communications ZyWALL 2Plus User Manual

This chapter describes how to configure bridge settings. This chapter is only applicable when
the ZyWALL is in bridge mode.

6.1 Bridge

The ZyWALL can serve as a transparent firewall (also known as a bridge firewall) in order to
provide firewall protection against denial of service attacks without. You do not need to
change your existing network configuration to use the ZyWALL as a bridge firewall. The
ZyWALL acts as a bridge between a switch and a wired LAN or between two routers and
filters and inspects the packets.

6.1.1 Bridge Loop

Be careful to avoid bridge loops when you enable bridging in the ZyWALL. Bridge loops
cause broadcast traffic to circle the network endlessly, resulting in possible throughput
degradation and disruption of communications. The following example shows the network
topology that can lead to this problem.
The ZyWALL (in bridge mode) is connected to a wired LAN while communicating with
another bridge or a switch that is also connected to the same wired LAN. So traffic will circle
the network

Figure 39 Bridge Loop: Bridge Connected to Wired LAN

You can prevent bridge loops by ensuring that your ZyWALL is not set to bridge mode while
connected to two wired segments of the same LAN. If your network uses RSTP, you can set
the ZyWALL to bridge mode while connected to two wired segments of the same LAN as long
as you enable RSTP on the ZyWALL and the LAN's other networking devices.

Chapter 6 Bridge Screens

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