Can you make a root port a designated port?

July 9, 2008 @ 7:09 pm · Filed under CCIE Study

Hi,
We can make a switch the root for some set of VLANs, and non-root for another set of VLANs. Similarly, we can make a switch port a root port for one set of VLANs, and a designated port for another set of VLANs.
Depending on the exact wording of the question, making a port both a root port and a designated port can be complished. Cheers,
—–Original Message—– From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of Scott Morris Sent: Thursday, 10 July 2008 3:31 AM To: ‘John’; ccielab@groupstudy.com Subject: RE: Can you make a root port a designated port?
It’s not possible to be both. Think about it…
A root port is your SWITCH’s decision that this is the best path back to the root bridge.
A designated port is the LINK’s “decision” that this is the best path back to the root bridge.
Assume we’re talking a link from Cat1-Cat2. So if the link elects Cat2 as the designated port, that means that everything from downstream (Cat1) should see that as the best path. If Cat2 tries to say that same port is the root port, that means everything FROM Cat2 goes out the port (in collision with the first statement).
So logically we’d have some difficulty there. Designated port is a “come to me” idea. Root port is an “I’ll go this way” idea.
HTH,
Scott Morris, CCIE4 #4713, JNCIE-M #153, JNCIS-ER, CISSP, et al. CCSI/JNCI-M/JNCI-ER Senior CCIE Instructor
smorris@internetworkexpert.com

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—–Original Message—– From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of John Sent: Wednesday, July 09, 2008 12:23 PM To: ccielab@groupstudy.com Subject: Can you make a root port a designated port?
I have a switch with 3 connections to another switch that is the root. One of the connections is a dot1q trunk. I’m tasked with making it a designated port. I have tried a number of configurations and I’ve come to realize that I cant make it designated because that would mean that one of the other ports has to become root. If I could then make make the port designated I have a loop.
Ports going to the root can only have two states root forwarding or altn blocking right?
Can anyone see a way to accomplish this? besides making my switch the root?

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