Blocking and Non-blocking

Unanswered Question
Aug 22nd, 2007

I was wondering what is the way to determine if a Catalyst switch is blocking or non-blocking. these terms are used in my work enviornment a lot and I know more or less what is a blocking and/or non-blocking switch, but I do not know how to determine it by looking at the hardware configuration of a switch.

I have this problem too.
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Jon Marshall Wed, 08/22/2007 - 09:16


As Bill suggested you may be referring to spanning tree and blocked ports.

However you could also be referring to the actual switch architecture ie. how many ports it has, what speeds the ports can run at, how much bandwidth the switchh fabric has.

If this is what you are referring to the best thing to do is to look at the data sheets for each switch. In there it will gives you figures such as switch fabric capacity etc. and with some simple maths you should be able to work these things out.

The same applies to mdular switches (4500 + 6500) although it can be a little more complicated.



jwdoherty Wed, 08/22/2007 - 10:03

If the type of blocking your asking about, i.e. whether a packet moving through a switch is blocked by another packet, such as head-of-line blocking, depends very much on the architecture of the switch. This is something that usually isn't visible via configuration. Where you might find this information is on the product's data sheets. Vendors won't highlight the lack of a feature of their product, so if they don't state it's a non-blocking switch you'll need to confirm whether it is or isn't. You might need to get a technical product rep to answer the question.


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