Question about Stacking and Trunk Uplinks

[osmhquser]

I was reviewing topology at one of my field offices and noticed they are using Cisco 3750 switches that are stacked with the stack-wise cable. Additionally I noticed they had connected one port to the other port on the switches that are in the stack together as a trunk. Does this cause an issue where they have a trunk port between the two switches connected which are also stacked together?

Thx in advance for any info provided. 

[Reza Sharifi · Accepted solution]

When the switches are stacked, there is no need to connect one switch to another via a cooper or fiber port, as the switch stack logically is one switch.  It is like connecting 2 ports together on the same switch. It can cause loop.

HTH

[osmhquser]

Thx for the response.

[Joseph W. Doherty]

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Posting

If the stack has an active Stack link, as Reza notes, it creates a loops (which should be blocked, by default, by STP).

If only one stack cable was used, instead of two, perhaps it was thought this would provide redundancy if the single stack cable failed.  If so, what it will do is allow two (partitioned) switches on the network "thinking" they are the same device (STP may unblock).  I.e. not good!  Redundancy should be provided by using a second stack cable.