Spanning tree

[Sharanjeet_Kumar]

Hello all,

1.Can I decrease the timers of stp?

2. What will be the effect of decreasing and increasing stp timers?

[marce1000]

 - FYI : https://www.cisco.com/c/en/us/support/docs/lan-switching/spanning-tree-protocol/19120-122.html

 M.

[Sharanjeet_Kumar]

Hi @marce1000 ,

i already went through it, but not satisfied that.

[ammahend]

What are you trying to achieve ? 

[Sharanjeet_Kumar]

Hi @ammahend ,

Not getting you.

just want know effect on my network when i decrease stp timers??

[ammahend]

Sorry couldn’t reply earlier, been busy. Anyways i see you got a solution and help. 

[balaji.bandi]

How extensive is your L2 network, why are you looking to change the timers ? it's all that you were looking to do in the network - what STP you deployed MST and PVST / Rapid STP - sometimes it's good to have lower timers - Rapid STP always converges faster. 

[Sharanjeet_Kumar]

Hi @balaji.bandi 

Thanks for your precious time,

i just want know what will be the effect of decreasing stp timers in my network?

will it fast the traffic or overwhelmed??

[balaji.bandi]

will it fast the traffic or overwhelmed??  - this is nothing to do with the results or timers as per I know if we talk about convergence timers. 

the timers are between 2 devices how fast they converge and your network. this required to change all over where required to get optimal.

until you have a major issue with timers - I would not suggest playing with it. (until you are clear about what you doing)

I would suggest reading @marce1000 provided document which explains. or provide your infrastructure details

[MHM Cisco World]

cisco recommend not adjuect the BPDU STP timers but instead 
you can do bypass some stage in STP process 


what feature can do that ?
portfast can go from BLK to FWD. this reduce the time of STP.
where I can apply portfast ?
in any port connect to host not to other SW
is portfast safe ?
it safe to use and there is additional feature called BPDU guard can also give you more protect to portfast port. 
protect from what ?
protect from form L2 Loop.

[Sharanjeet_Kumar]

Hi @MHM Cisco World  

thanks for your precious time,

but i think i asked the effect on my network of spanning tree timers increasing or decresing?

[MHM Cisco World]

I think one lab will explain to you effect of timer,

I will share it today 

[Sharanjeet_Kumar]

Thanks @MHM Cisco World.

Waiting for the lab content.

[MHM Cisco World]

I try play with diameter in my lab, and show you the effect of max age and time to receive the BPDU, but I failed. 
anyway 
I recommend not play with time.
and as I mention before bypass phase is better.

[paul driver · Accepted solution]

Hello

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@Sharanjeet_Kumar wrote:

Hello all,

1.Can I decrease the timers of stp?

2. What will be the effect of decreasing and increasing stp timers?

---

If you change the stp diameter for the estate this will automatically recalculate the stp maximum/forwarding delay timers to accommodate that change, be it by increasing/decreasing the timers.

A smaller diameter will mean faster the convergence!

Diameter = default=7 ( range 2 to 7)

Example:
Switch(config)#do sh spanning-tree | in Hello

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

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

Switch(config)#spanning-tree vlan 1-4094 root primary diameter 2

Switch(config)#do sh spanning-tree | in Hello

             Hello Time   2 sec  Max Age 10 sec  Forward Delay  7 sec

             Hello Time   2 sec  Max Age 10 sec  Forward Delay  7 sec