How Stp Works; Stp Port States; Dfs - ZyXEL Communications NWA-3160 User Manual

Chapter 8 Wireless Screen

8.3.5.3 How STP Works

After a bridge determines the lowest cost-spanning tree with STP, it enables the
root port and the ports that are the designated ports for connected LANs, and
disables all other ports that participate in STP. Network packets are therefore only
forwarded between enabled ports, eliminating any possible network loops.
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.

8.3.5.4 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.
Table 31 STP Port States
PORT
STATES
Disabled
Blocking
Listening
Learning
Forwarding

8.3.6 DFS

When you choose 802.11a in Access Point mode, the NWA uses DFS (Dynamic
Frequency Selection) to give you a wider choice of wireless channels.
DFS allows you to use channels in the frequency range normally reserved for
radar systems. Radar uses radio signals to detect the location of objects for
military, meteorological or air traffic control purposes. As long as your NWA
detects no radar activity on the channel you select, you can use the channel to
communicate. However, a wireless LAN operating on the same frequency as an
active radar system could disrupt the radar system. Therefore, if the NWA detects
radar activity on the channel you select, it automatically instructs the wireless
132
DESCRIPTIONS
STP is disabled (default).
Only configuration and management BPDUs are received and processed.
All BPDUs are received and processed.
All BPDUs are received and processed. Information frames are
submitted to the learning process but not forwarded.
All BPDUs are received and processed. All information frames are
received and forwarded.
NWA-3160 Series User's Guide