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Command-output "show spanning-tree uplinkfast"

I have a question regarding the "show spanning-tree uplinkfast" command.

I know what uplinkfast does and how but I couldn't find documentation for the show-command.

A couple of switches in our network have an output like this one:

Command :show spanning-tree uplinkfast | i Number of

===============

Number of transitions via uplinkFast (all VLANs) : 51

Number of proxy multicast addresses transmitted (all VLANs) : 10920

If the transitions/multicasts are greater then 0, the backup-link must have been activated respectively the uplink must have been inactive, right?

This is what worries me, because I see many switches with counters > 0, and I normally wouldn't expect this in a stable network.

  • LAN Switching and Routing
1 ACCEPTED SOLUTION

Accepted Solutions

Re: Command-output "show spanning-tree uplinkfast"

Hi Rolf,

An uplinkfast transition happens as a result of a configuration of the network (parameter change, link added/removed, switch reloaded etc...) or a failure (loss of bpdus, link going down etc...).

So if your sporadic uplinkfast transitions occur as a result of sporadic configuration events, I would not worry about them.

However, if you experience sporadic uplinkfast transitions while being sure that there is no configuration event, I would try to investigate their source.

Regards,

Francois

3 REPLIES

Re: Command-output "show spanning-tree uplinkfast"

The most important is how those figures are evolving I guess.

If you have 51 vlans, it could be a single transition. If the alternate port(s) came up before the current root port, there might have been an uplinkfast transition without any failure. And this transition might have occurred 1 year ago;-) In that case you should not be worried.

On the other hand, you can have a single vlan that had its root port flapping 51 times in the last hour. In which case you might have indeed something going on.

It's impossible to make a difference between those two cases with just one snapshot.

Regards,

Francois

New Member

Re: Command-output "show spanning-tree uplinkfast"

Francois,

thanks for the answer - this is an interesting point! We actually have nearly 50 VLANs and when I include all the default VLANs, it could be 51.

The reason why I'm monitoring things like that is that we sporadically see "Hostflapping" syslog messages and the MAC-Adress is always flapping between the uplink-port and a local access-port. First I couldn't understand how this can happen but now I'm convinced that it's related to this Uplinkfast swichovers.

And as long as this happens only sporadically I really don't have to worry, do I?

Re: Command-output "show spanning-tree uplinkfast"

Hi Rolf,

An uplinkfast transition happens as a result of a configuration of the network (parameter change, link added/removed, switch reloaded etc...) or a failure (loss of bpdus, link going down etc...).

So if your sporadic uplinkfast transitions occur as a result of sporadic configuration events, I would not worry about them.

However, if you experience sporadic uplinkfast transitions while being sure that there is no configuration event, I would try to investigate their source.

Regards,

Francois

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