Here are the answers:
The Hello Timer triggers periodic ?hello? (actually the Configuration BPDU) messages that are sent
from the Root to other bridges in the network. This timer also sets the interval in which a bridge
expects to hear a hello relayed from its neighboring bridges. Configuration BPDUs are sent every
2 seconds, by default. You can modify the Hello Timer per VLAN with the hello-time keyword,
along with a value of 1 to 10 seconds.
The Forward Delay Timer determines the amount of time a port stays in the Listening state before
moving into the Learning state and how long it stays in the Learning state before moving to the
Forwarding state. You can modify the Forward Delay Timer per VLAN with the forward-time
keyword. The default value is 15 seconds but can be set to a value of 4 to 30 seconds. This timer
should be modified only under careful consideration because the value is dependent upon the
diameter of the network and the propagation of BPDUs across all switches. A value too low allows
loops to form and cripples a network.
The MaxAge Timer specifies a stored BPDU?s lifetime that has been received from a neighboring
switch with a Designated Port. Suppose BPDUs are being received on a non-Designated switch port
every 2 seconds, as expected. Then an indirect failure, or one that doesn?t involve a physical link
going down, occurs that prevents BPDUs from being sent. The receiving switch waits until the Max
Age Timer expires to listen for further BPDUs. If none are received, the non-Designated Port moves
into the Listening state, and the receiving switch generates Configuration BPDUs. This port then
becomes the Designated Port to restore connectivity on the segment.
To modify the Max Age Timer on a per-VLAN basis, use the max-age keyword. The timer value
defaults to 20 seconds but can be set from 6 to 40 seconds.
bye
FCS
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