ZyXEL Communications 5 Series - Manual (Page 143)

ZyWALL 5/35/70 Series User’s Guide
Chapter 7 Bridge Screens 143
STP-aware bridges exchange Bridge Protocol Data Units (BPDUs) periodically. When the
bridged LAN topology changes, a new spanning tree is constructed.
Once a stable network topology has been established, all bridges listen for Hello BPDUs
(Bridge Protocol Data Units) transmitted from the root bridge. If a bridge does not get a Hello
BPDU after a predefined interval (Max Age), the bridge assumes that the link to the root
bridge is down. This bridge then initiates negotiations with other bridges to reconfigure the
network to re-establish a valid network topology.
7.2.4 STP Port States
STP assigns five port states (see next table) to eliminate packet looping. A bridge port is not
allowed to go directly from blocking state to forwarding state so as to eliminate transient
loops.
7.3 Bridge
Select Bridge and click Apply in the MAINTENANCE Device Mode screen to have the
ZyWALL function as a bridge.
In bridge mode, the ZyWALL functions as a transparent firewall (also known as a bridge
firewall). The ZyWALL bridges traffic traveling between the ZyWALL's interfaces and still
filters and inspects packets. You do not need to change the configuration of your existing
network.
You can use the firewall and VPN in bridge mode.Click NETWORK > BRIDGE to display
the screen shown next. Use this screen to configure bridge and RSTP (Rapid Spanning Tree
Protocol) settings.
Table 28 STP Port States
PORT STATE DESCRIPTION
Disabled STP is disabled (default).
Blocking Only configuration and management BPDUs are received and processed.
Listening All BPDUs are received and processed.
Learning All BPDUs are received and processed. Information frames are submitted to the
learning process but not forwarded.
Forwarding All BPDUs are received and processed. All information frames are received and
forwarded.