Spanning Tree will run its algorithm every time a port is plugged in (unless
Portfast is enabled...) and ensure a loop free topolgy. The first port up
will not necessarily be the one that stays in forwarding, it depends on
several variables... bridge ID, cost to root, port priority... all of which
are sent out in STP BPDUs.
I would recommend you get a copy of the Cisco Press book Cisco LAN
Switching. The two chapters on STP (and the rest of the book, too) are
probably the best written. Well worth the $60 or so.
/Jared
-----Original Message-----
From: Jon Mitchell [mailto:[EMAIL PROTECTED]]
Sent: Friday, September 29, 2000 10:16 AM
To: Bradley J. Wilson
Cc: [EMAIL PROTECTED]
Subject: Re: STP question
On Fri, Sep 29, 2000 at 09:36:46AM -0400, Bradley J. Wilson wrote:
> Spanning Tree Protocol, which I'm assuming is what you're referring to,
> doesn't have anything to do with routing. If you were connecting bridges
> together in a loop, STP would break the loop and you'd be fine. In your
> case, the mechanism which will prevent routing loops is split horizon
> (assuming you're running RIP), which is on by default.
Sorry, I meant to say switch, wrote this too early in the morning
evidently. So you are saying that STP does not only negotiate at switch
startup, it will constantly detect new loops that are added? If so,
another question would be whether I could guarentee that it would be this
switch's port that would block to prevent the loop. Or would it just be
the first switch that detects the problem?
The network looks like this:
------------ ------------
| Switch A |-------------| Switch B |
------------ ------------
| |
| <------ This is link I plugin.
------------ ------------
| Switch C |-------------| Switch D |
------------ ------------
So if switch D is then plugged in, will it start STP negotiation on the
port even though the switch has already booted? Or will one of the
switches randomly discover the loop after the link is already forwarding
traffic and disable it's interfaces?
--
Jon Mitchell
Systems Engineer, Subject Wills & Company
[EMAIL PROTECTED]
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