spanning tree network diameter

Unanswered Question
Jul 9th, 2007

I have read that the cisco recommended network diameter is 7 for STP. I was wondering if someone could further define this number for me? For example, if there is a set of 7 switches (3550 and 2950)linked together with gigastack uplinks and 2 fibre trunks to a 4006--does this exceed the network diameter? Likewise is the network diameter the actual amount of switches in same native vlan 1--for example multiple stacks (about 20 switches--none of which greater than the stack of 7 mentioned earlier in a looped stack back to the 4006) of switches all coming back to the 4006 all using vlan 1 as the native vlan and management vlan.

I have this problem too.
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Amit Singh Mon, 07/09/2007 - 20:30


With IEEE 802.1d,recommended consideration when designing the network with STP is not more than 7 hops. On the default timer parameters STP is expected to work fine till 7 hops. Beyond 7 hops the STP will work but it might bit a little hard to predict the behaviour of the STP, which might result in a lots of network problems. From an individual switch perspective like from the root bridge the STP diameter should not be more than 7 hops away.

As per your topology above, I dont think so that you will exceed this diameter,it actually depends on the rootbridge placement.Whenever you are configuring the rootbrige on your network, you have to make sure that the none of switch should be 7 hops away in connectivity. If you are following Cisco's 3-tier hierarchical design you will never be exceeding the STP diameter, hence you should not be worrying about it much.

HTH,Please rate if it does.

-amit singh


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