STP,switch diameter constraint

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Feb 23rd, 2004
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Hello,


in BCMSN book, "STP Timers" and "Tuning STP Convergence" sections include a constraint about "a switched STP network with redundant paths should not include more than seven switches".


And we have 8 switches cascaded.I'll plan to make the links redundant. Or in the future out L2 swithed network may grow.


---Should i take into consideration this issue?

---if yes,should i terminate L2 network with an high performance router?


thanks


BERKIN KARTAL

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milan.kulik Mon, 02/23/2004 - 00:28
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Hi,

I've got network diameter 9 without any problem.

But you should definetely take this isuue into consideration when your network grows and try to make the network diameter as small as possible.

Read http://www.cisco.com/warp/public/473/122.pdf for better understanding.


Regards,

Milan


Odissefs Mon, 02/23/2004 - 00:34
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should i have to set "spannin-tree vlan #id root {primary | secondary} [diameter #value] " ?


regards


BERKIN

milan.kulik Tue, 02/24/2004 - 00:44
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Generally, it's always better when YOU choose which switch should become STP root in your network and configure it via spanning tree root macro, e.g. (don't forget root is per-VLAN feature while using PVSTP).

According to your STP diameter problem: this command won't help you, the diameter range is 2-7. It can be useful to decrease the STP timers when your network diameter is small (3, e.g) and make the STP convergence faster. But the default timers are set for diameter 7, so root macro won't change them in your case.

You could tune the timers according to the document I linked in the previous message, but I think it has no sence for diameter 8. Tuning the STP parameters is always a very sensitive thing.


Regards,

Milan

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