Chapter 5 Bridge Screens; Bridge Loop; Spanning Tree Protocol (Stp); Figure 5-1 Bridge Loop: Bridge Connected To Wired Lan - ZyXEL Communications ZyWALL 5 User Manual

This chapter describes how to configure bridge settings. This chapter is only applicable when
5.1

Bridge Loop

The ZyWALL can act as a bridge between a switch and a wired LAN or between two routers.
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:
If your 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 as shown next.

Figure 5-1 Bridge Loop: Bridge Connected to Wired LAN

To prevent bridge loops, ensure that your ZyWALL is not set to bridge mode while connected to two
wired segments of the same LAN or you enable RSTP in the Bridge screen.
5.2

Spanning Tree Protocol (STP)

STP detects and breaks network loops and provides backup links between switches, bridges or routers.
It allows a bridge to interact with other STP-compliant bridges in your network to ensure that only one
route exists between any two stations on the network.
5.2.1 Rapid STP
The ZyWALL uses IEEE 802.1w RSTP (Rapid Spanning Tree Protocol) that allow faster convergence
of the spanning tree (while also being backwards compatible with STP-only aware bridges). Using
RSTP topology change information does not have to propagate to the root bridge and unwanted
learned addresses are flushed from the filtering database. In RSTP, the port states are Discarding,
Learning, and Forwarding.
Bridge Screens
ZyWALL 5 Internet Security Appliance
Chapter 5
Bridge Screens
the ZyWALL is in bridge mode.
5-1