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RSTP convergence times?

Hi,

Can you let me know who much time does RSTP take to re-converge? Like how much time would it take a port to go from BLK/Discarding to Forwarding?

Theory says less than 10 secs, BUT i need the actual practical timers. !! Please Advise.

6 REPLIES

RSTP convergence times?

http://en.wikipedia.org/wiki/Spanning_Tree_Protocol

In 2001, the IEEE introduced Rapid Spanning Tree Protocol (RSTP) as 802.1w. RSTP provides significantly faster spanning tree convergence after a topology change, introducing new convergence behaviors and bridge port roles to do this. RSTP was designed to be backwards-compatible with standard STP.

While STP can take 30 to 50 seconds to respond to a topology change, RSTP is typically able to respond to changes within 3 × Hello times (default: 3 times 2 seconds) or within a few milliseconds of a physical link failure. The so-called Hello time is an important and configurable time interval that is used by RSTP for several purposes; its default value is 2 seconds.[7][8]Standard IEEE 802.1D-2004 now incorporates RSTP and obsoletes the original STP standard.

I can tell you from a real world network - I have seen a blocked port transition to forwarding in under 10 msec.

Purple

RSTP convergence times?

  In installations we have used the convergence times is generally less than 3 seconds if configured correctly.

Cisco Employee

RSTP convergence times?

indeed, I am not sure where you got that 10 secs value. Rapid convergence of RSTP is achieved by the use of timer-independent ‘proposal-agreement’ handshake so it is difficult to say a given value.

RSTP convergence times?

Hi,

See the below discussion may give you clear picture.

http://www.techexams.net/forums/ccna-ccent/52440-stp-vs-rstp-convergence-times.html

Please rate the helpfull posts.

Regards,

Naidu.

Bronze

RSTP convergence times?

Just some remarks: if both ends of a link are RSTP and use the proposal-agreement phase, they can converge very rapidly, i am talking maximum 2-3 seconds. I have once seen a situation where it took up to 6 seconds to converge to backup links. Upon troubleshooting, this was caused by the fact that the remote side did not talk STP at all (or no RSTP in every case). If the remote-end does not reply to a "proposal" packet, it will take 6 seconds before this "proposal" attempt times out and normal non-proposal convergence kicks in...

Cisco Employee

RSTP convergence times?

I have not done some big installtions but RSPT has converged very rapidly in some of the tests that I have done for customers. It all depends on how big your topology is and what kind of traffic you have on the network. In some of the tests that I have done with Cat6K, Cat4500 and Cat3750 with RPVST enabled and voice/video/wireless traffic on the switches, it converged rapidly without voice/video calls getting dropped, wireless users getting reassociated in link failure scenarios. We did some of the parameters tuning in some cases but even with the default timers, it was a rapid convergence.

Hope this helps.

Cheers,

-amit singh

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