Nortel 6220 User Manual page 105

When the bridge receives protocol information that exceeds the Max Age
value, the bridge will discard the information and start the Forward
Delay timer to allow other bridges to forward updated topology
information (for example, that another bridge has become the Root
Bridge).
Note: Recommended Value (20 seconds)
A low Max Age value occasionally may cause the Spanning Tree to
reconfigure unnecessarily, resulting in temporary loss of connectivity
throughout the network.
A high Max Age value will cause the LAN to take longer than necessary
to rebuild the Spanning Tree whenever a link or bridge unit breaks down
or becomes available again.
Hello Time -- The Spanning Tree Hello Time parameter identifies the
time interval between Configuration PBDU transmitted by a root bridge,
or a bridge that is attempting to become the root bridge.
Note: Recommended Value (2 seconds)
Shortening the Hello Time will make the protocol more robust,
especially when the probability of loss of configuration messages is high.
Lengthening the Hello Time will lower the overhead of the algorithm
since the interval between the transmissions of configuration messages
will be longer.
Forward -- The Forward Delay is a timer that prevents a bridge to
forward data packets when:
• The bridge receives information that the active Spanning Tree
topology must be updated (for example when a bridge breaks down
or when somebody modified the Bridge Priority or Path Cost value of
a particular bridge).
• The bridge registers that the protocol information exceeds the
specified Max Age value.
• Changes in the Spanning Tree topology must be communicated to all
bridges in the bridged network. The Forward Delay timer will
compensate for the propagation delays that occur in passing the
protocol information, allowing all bridges to close the old data paths,
before the new data paths are activated.
Note: Recommended Value (15 seconds)
A lower value may result in temporary loops as the Spanning Tree
Algorithm converges.
WLAN Cable Access Point 6220 CSU NTPM99CA Rel 2.0 Issue 5 Dec 2005
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