Reference v4.1.0 Instruction Manual

Network OS Command Reference 311

53-1003115-01

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 time that an interface spends in the Spanning Tree Protocol

(STP) learning and listening states. Valid values range from 4 through 30

seconds.

Defaults 15 seconds

Command Modes Protocol Spanning Tree 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.

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.

Usage Guidelines 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)

If xSTP is enabled over VCS, this command must be executed on all the RBridge nodes.

Enter no forward-delay to return to the default settings.

Examples To configure the forward-delay time to 18 seconds:

switch(conf-mstp)# forward-delay 18