Cisco 7 Switches diameter

Answered Question
Jul 30th, 2007
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Hi All


Pls can anyone explain what is meant by the 7 Switches diameter recommended by Cisco?


I have about 2 core switches with 10 switches connected into each of them in an uplink. Then on one of the core Switch, I have a 1GB link to about 10 other switches in chain fashion.


Where do I get the 7 switches? I do not want to exceed but how to I count this diameter?


Thanks






Correct Answer by Jon Marshall about 9 years 10 months ago

Hi


If you have a core switch and connected to this switch are 10 switches so each switch has one connection to the core switch this is a diameter of 1.


It's not the number of switches it's how the are connected. So


core switch -> switch1 -> switch2 -> switch3.


If you have switches connected in the above fashion then your diameter is 3.


HTH


Jon

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Correct Answer
Jon Marshall Mon, 07/30/2007 - 02:15
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Hi


If you have a core switch and connected to this switch are 10 switches so each switch has one connection to the core switch this is a diameter of 1.


It's not the number of switches it's how the are connected. So


core switch -> switch1 -> switch2 -> switch3.


If you have switches connected in the above fashion then your diameter is 3.


HTH


Jon

londint Mon, 07/30/2007 - 02:26
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Thank you very much. I understand it now perfectly. Thanks

balajitvk Mon, 07/30/2007 - 02:26
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Hi,


The default timers of STP (Hello, Forwarding Delay and Max Age) are based on an assumption of the diameter of the network. i.e They have a default as 7 hops / switches.


But you can change the STP timers such that to accomdate more hops, but the same is not advisable.


Hope this will clear ur doubt.


Rate if it does,

Rgs.

Amit Singh Mon, 07/30/2007 - 03:54
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Hi,



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, and posted by Jon you will not 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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