Technical data

Converged Enhanced Ethernet Command Reference 73
53-1002508-01
forward-delay
2
forward-delay
Specifies the time an interface spends in each of the listening and learning states.
Synopsis forward-delay seconds
no forward-delay
Operands seconds Specifies the range of time in seconds that an interface spends in the
Spanning Tree Protocol (STP) learning and listening states. The range of valid
values is from 4 through 30.
Defaults The default is 15 seconds.
Command
Modes
Spanning Tree Protocol configuration mode
Description Use this command to specify how long the listening and learning states last before the interface
begins the forwarding of all spanning-tree instances. Use the no forward-delay command to return
to the default settings.
Usage
Guidelines
STP interface states:
• Listening - The interface processes the Bridge Protocol Data Units (BPDUs) and awaits possible
new information that might cause it to return to the blocking state.
• Learning - The interface does not yet forward frames (packets). Instead it learns source
addresses from frames received and adds them to the filtering database (switching database).
• Forwarding - An interface receiving and sending data (normal operation). STP still monitors
incoming BPDUs that can indicate it should return to the blocking state to prevent a loop.
• Blocking - An interface that can cause a switching loop (no user data is sent or received), but it
might go to the forwarding state if the other links in use fail and the STP determines that the
interface may transition to the forwarding state. BPDU data continues to be received in the
blocking state.
When you change the spanning-tree forward-delay time, it affects all spanning-tree instances.
When configuring the forward-delay, the following relationship should be kept:
2*(forward-delay - 1)>=max-age>=2*(hello-time + 1)
Examples To configure the forward-delay time to 18 seconds:
switch(conf-mstp)#forward-delay 18
See Also hello-time, max-age, max-hops