spanning tree forward timers

Unanswered Question
Oct 24th, 2007

I want to set up the forwarding time to 12 sec. please let me know how to do .

I have this problem too.
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mark.cronin Wed, 10/24/2007 - 05:50

Are you talking about spanning tree forwarding?

SW1(config)#spanning-tree vlan 1 forward-time 6

listening

learning

forwarding

shivlu jain Wed, 10/24/2007 - 05:53

your answer is 100% correct. But please let me know how to calculate this.

shivlu

Kevin Dorrell Wed, 10/24/2007 - 05:54

Are you running PVST? This must be done on the root:

spanning-tree vlan n forward-time 12

This will give you 12 seconds of listening state and 12 seconds of learning.

That is OK provided the diameter of your network is less than about 5 switches. Otherwise you could be introducing some instability.

Kevin Dorrell

Luxembourg

shivlu jain Wed, 10/24/2007 - 05:57

yeh my diameter is less than 4 switches. But still i am not clear. Do you have the formula for the same.

becasue i want to set the forward time to 20 seconds thn i donot want to disturb you again. So please let me know how to calculate this.

regards

shivlu

mark.cronin Wed, 10/24/2007 - 06:00

Kevin

If he wants the switchport to forward 12 seconds after the port is UP/UP will he need to use 6

6 learning

6 forwarding

spanning-tree vlan n forward-time 6

shivlu jain Wed, 10/24/2007 - 06:04

y u right mark, kevin the same i was trying what you said but it wonot work.

So mark if i want to set the forard time to 20 seconds thn i have to use the command

spnnaing tree vlanid forward 10

shivlu

bvsnarayana03 Wed, 10/24/2007 - 06:25

Best practices indicate, not to vary STP timers but diameter, which then automatically varies the timers based on calculation.

Command is:

spanning-tree vlan vlanid# root primary diameter {No.}

This has to be configured on the root bridge. The diameter value will not be reflected in configuration, only the timer values will be displayed.

Francois Tallet Wed, 10/24/2007 - 08:32

Best practices mainly indicate that you need to know what you're doing when you plan on tuning STP timers;-) What are you trying to achieve? Why do you say that tuning the forward time does not work? (is it based on the port going to forwarding using a different timer, the show command? or the CLI confusing you?)

c3750-ts37#sh span vlan 1

VLAN0001

Spanning tree enabled protocol rstp

Root ID Priority 1

Address 0016.9dba.e280

This bridge is the root

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 1 (priority 0 sys-id-ext 1)

Address 0016.9dba.e280

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Aging Time 300

Interface Role Sts Cost Prio.Nbr Type

---------------- ---- --- --------- -------- --------------------------------

Fa2/0/1 Desg FWD 19 128.55 P2p

Fa2/0/2 Desg FWD 19 128.56 P2p

Fa2/0/3 Desg FWD 19 128.57 P2p

Fa2/0/4 Desg FWD 19 128.58 P2p

Fa2/0/5 Desg FWD 19 128.59 P2p

Fa2/0/6 Desg FWD 19 128.60 P2p

Fa2/0/7 Desg FWD 19 128.61 P2p

Fa2/0/8 Desg FWD 19 128.62 P2p

c3750-ts37#conf t

Enter configuration commands, one per line. End with CNTL/Z.

c3750-ts37(config)#span vlan 1 for

c3750-ts37(config)#span vlan 1 forward-time 12

c3750-ts37(config)#^Z

c3750-ts37#sh span vlan 1

VLAN0001

Spanning tree enabled protocol rstp

Root ID Priority 1

Address 0016.9dba.e280

This bridge is the root

Hello Time 2 sec Max Age 20 sec Forward Delay 12 sec

Bridge ID Priority 1 (priority 0 sys-id-ext 1)

Address 0016.9dba.e280

Hello Time 2 sec Max Age 20 sec Forward Delay 12 sec

Aging Time 300

Interface Role Sts Cost Prio.Nbr Type

---------------- ---- --- --------- -------- --------------------------------

Fa2/0/1 Desg FWD 19 128.55 P2p

Fa2/0/2 Desg FWD 19 128.56 P2p

Fa2/0/3 Desg FWD 19 128.57 P2p

Fa2/0/4 Desg FWD 19 128.58 P2p

Fa2/0/5 Desg FWD 19 128.59 P2p

Fa2/0/6 Desg FWD 19 128.60 P2p

Fa2/0/7 Desg FWD 19 128.61 P2p

Fa2/0/8 Desg FWD 19 128.62 P2p

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