Cisco Support Community

explanation of "hello-time,forward-time & max-age" in spanning-tree


what is the exact meaning for the following command using in spanning-tree?

spanning-tree vlan 1-2,5,175,182-205 hello-time 1

spanning-tree vlan 1-2,5,175,182-205 forward-time 4

spanning-tree vlan 1-2,5,175,182-205 max-age 6


Re: explanation of "hello-time,forward-time & max-age" in spanni

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.



Please rate me if I helped.

CreatePlease to create content