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Looping Catalyst switches

priffe
Level 1
Level 1

‎07-11-2003 10:50 AM - edited ‎03-02-2019 08:48 AM

The current situation is this:

3 Switches ( 1,2 and 3) with 2 gigabit cards each ( a and b). 2A connected to 1B, 2B connected to 3A. The world is happy, traffic is flowing. We installed another switch ( Gigabit 4A and 4B)and for redundancy connected 4A to 3B and 4B to 1A so if one of the cables failed there would still be a path. As I found out, this doesn't work. I am thinking spanningtree will rectify this but am not sure

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Bobby Thekkekandam
Cisco Employee
Cisco Employee

‎07-11-2003 11:07 AM

Yes,

by introducing the 4th switch, you are creating a physical loop. If you have spanning tree protocol disabled, then your switches will not forward traffic properly in this scenario.

Make sure spanning tree protocol is enabled, and it will logically block one of the ports so that traffic is not looped.

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