I thought that this would be prevented by default because of spanning 
tree/BPDU, but it’s common practice to disable spanning tree for access ports 
(i.e. using portfast) so that may allow the loop to occur, so maybe just 
disable port-fast?

Kind Regards

Stephen Welsh
CTO

[cid:[email protected]]

On 10 Nov 2016, at 13:35, Ahmed Elnagar 
<[email protected]<mailto:[email protected]>> wrote:

That is not nice at all ☹

Did you figure out a way to prevent it from switch side?

From: Matthew Loraditch [mailto:[email protected]]
Sent: Thursday, November 10, 2016 3:34 PM
To: Ahmed Elnagar 
<[email protected]<mailto:[email protected]>>; 
'[email protected]<mailto:[email protected]>' 
<[email protected]<mailto:[email protected]>>
Subject: RE: IP Phone Ports

Yes it will create a loop. Not a fun time trying to track these things down. 
I’ve had some non-Cisco IP phones completely down a LAN.

Matthew G. Loraditch – CCNP-Voice, CCNA-R&S, CCDA
Network Engineer
Direct Voice: 443.541.1518
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From: cisco-voip [mailto:[email protected]] On Behalf Of Ahmed 
Elnagar
Sent: Thursday, November 10, 2016 8:28 AM
To: '[email protected]<mailto:[email protected]>' 
<[email protected]<mailto:[email protected]>>
Subject: [cisco-voip] IP Phone Ports

Dear all;

I want to know what will happen if a user connect “by mistake” both the PC port 
and Switch port to the network switch? Will this create a loop? Anyone tried it 
before?


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