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RSTP

Posted on 2012-03-16
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Last Modified: 2012-04-09
How can I check the convergence time of my network using wireshark? If i have 2 switches and I purposly create a loop for testing purposes and then I break the link that is forwarding, i want to figure out how fast is my switch taking to forward traffic.

Thanks!!!
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Question by:TAMSCODAN
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8 Comments
 
LVL 50

Expert Comment

by:Don Johnston
ID: 37729825
Run a continuous ping between two hosts that cross between the switches. Then disconnect the forwarding link and see how long it takes for the pings to resume.
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LVL 3

Author Comment

by:TAMSCODAN
ID: 37730074
Thats not a good solution because there is a 1 second delay between Ping therefore i would not get an accurate reading in milliseconds. That is why i want to know how to do this on wireshark to get the actual interval. I have mirrored both the forwarding port and the discarding port but I really dont understand how to get the info on wireshark as to how long that transition is taking.
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LVL 50

Expert Comment

by:Don Johnston
ID: 37730457
Expecting spanning tree to converge in milliseconds is not practical.  The worst you should see (properly configured) is 2-3 seconds. The best I would expect is about 1 second.
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LVL 3

Author Comment

by:TAMSCODAN
ID: 37730472
RSTP as i understand it can also converge in appx 500ms on a small network. I am just trying to find the way to measure it on wireshark
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LVL 50

Expert Comment

by:Don Johnston
ID: 37730561
How fast depends on the failure mode.  Half-second convergence is like the old EPA gas mileage estimates. That's a best case scenario. 1-3 seconds is typical.
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LVL 3

Author Comment

by:TAMSCODAN
ID: 37730600
ok, regardless of the timing I just want to know how to get it documented on a capture using wireshark. I appritiate your help but I want to know how to verify this information.
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LVL 50

Expert Comment

by:Don Johnston
ID: 37730743
What kind of switches? Most managed switches log events. You should be able to see when a link goes down and when the blocking link starts to forward.
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LVL 15

Accepted Solution

by:
Nayyar HH (CCIE RS) earned 2000 total points
ID: 37765429
Enable timestamps and use "debug spanning-tree event"

This would displays all spanning tree events, such as changes to the root or to the status of any of the ports. Also shows progress through listening and learning states to forwarding state. So you should see convergence take place.


config t
service timestamps debug datetime msec
end
debug spanning-tree event
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