Regarding cascading 2960 switches

Unanswered Question
Aug 21st, 2008

Hi Experts ,

I would like to know the maximum number 2960 switches can be cascaded.

How many 2960 swutches we can connect in cascaded position.Is there any doc.

Thanks,

Satish

I have this problem too.
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satish_zanjurne Thu, 08/21/2008 - 22:32

Hi,

The conservative default values for the STP timers impose a maximum network diameter of seven. This maximum network diameter restricts how far away from each other bridges/switches in the network can be. In this case, two distinct bridges/switches cannot be more than seven hops away from each other

When a BPDU propagates from the root bridge toward the leaves of the tree, the age field increments each time the BPDU goes though a bridge/switch. Eventually, the bridge discards the BPDU when the age field goes beyond maximum age. If the root is too far away from some bridges/switch of the network, this issue can occur. This issue affects convergence of the spanning tree.

http://www.cisco.com/en/US/tech/tk389/tk621/technologies_tech_note09186a00800951ac.shtml

So it's 7 !!!

HTH..

smothuku Thu, 08/21/2008 - 22:44

Hi Satish ,

Thanks for the info.Is there any doc which specifies switch model and max.limit of switches can be connected in cascade position.

Thanks,

Satish

satish_zanjurne Thu, 08/21/2008 - 22:56

Use the diameter keyword to specify the Layer 2 network diameter (that is, the maximum number of switch hops between any two end stations in the Layer 2 network). When you specify the network diameter, the switch automatically sets an optimal hello time, forward-delay time, and maximum-age time for a network of that diameter, which can significantly reduce the convergence time. You can use the hello keyword to override the automatically calculated hello time

this is the document.

http://cisco.com/en/US/docs/switches/lan/catalyst2960/software/release/12.2_44_se/configuration/guide/swstp.html#wp1020804

Command is :

spanning-tree vlan vlan-id root primary [diameter net-diameter [hello-time seconds]]

(Optional) For diameter net-diameter, specify the maximum number of switches between any two end stations. The range is 2 to 7.

HTH..

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