What You Need To Know About Bridging; Figure 91 Bridge Loop: Bridge Connected To Wired Lan - ZyXEL Communications 5 Series User Manual

Chapter 8 Bridge Screens

8.1.2 What You Need To Know About Bridging

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:
• 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 91 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.
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.
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.
Finding Out More
To see more information on bridging refer to
To see more advanced information on bridging refer to
162
Section 33.5 on page 591.
Section 8.4 on page
ZyWALL 5/35/70 Series User's Guide
166.