Weird Scenario with switching

I have a weird scenario, trying to practice switching. I have three switches all connected in a triangle like shaped named switch 1, switch 2 and switch 3. When I break the connection between my switch 1, my switch 3 my connection between switch 3 and switch 2 will work, however when all are interconnected, my connection to switch 3 from switch 2 fails

I have attached the diagram of my switched network, what could be the cause of this, all interfaces are up when i do a shw ip interface brief, when I do a tracert from switch2 to switch 3 it goes the long way....

i have no port-security turned on right now

2014-03-30_19-59-10.png

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Comments

JeanM

Are you asking why a port is shut down on sw3 to sw2? STP in action.

http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst2950/software/release/12-1_9_ea1/configuration/guide/scg/swstp.html

EdTheLad

You need to do some reading on the spanning-tree protocol.

gbdavidx

JeanM wrote: »

Are you asking why a port is shut down on sw3 to sw2? STP in action

Catalyst 2950 Desktop Switch Software Configuration Guide, 12.1(9)EA1 - Configuring STP [Cisco Catalyst 2950 Series Switches] - Cisco

According to show IP iny brief all ports are up. The diagram is just showing the amber light

aftereffector

Sounds like you made yourself a spanning-tree lab.

gbdavidx

I understand its a STP issue but how do i fix it, i thought this was enabled by default on all switches or do i have to turn it on?

networker050184

What exactly are you trying to fix? This isn't an issue, it's the way STP works.

Dieg0M

If you want to make the light go green just "spanning-tree portfast". Enjoy the meltdown

OfWolfAndMan

Do you know what the purpose of STP is? Ever heard of a broadcast storm?

gbdavidx

yes and yes, read about it last night, to prevent loops, so this is by design? i'm just trying to grasp the idea and make sure its not something i did wrong

xnx

No, it's just how STP works, you'll cover it in ICND2

networker050184

STP prevents loops by ensuring there is no path for a loop to occur. To do this it creates a single path out from the root. Links that are not on this path do not forward traffic. That is what you are seeing here.

gbdavidx

thanks!

Jon_Cisco

If it allowed both connections to be established then the packets would send out both interfaces.
When a loop like this occurs packets will be duplicated continually.

It is worth disabling this and seeing it happen. Just make sure it's a simulation or a lab setup.

arrogantbastard

Jon_Cisco wrote: »

If it allowed both connections to be established then the packets would send out both interfaces.
When a loop like this occurs packets will be duplicated continually.

It is worth disabling this and seeing it happen. Just make sure it's a simulation or a lab setup.

It's the frames that are duplicated and cause mac instability/broadcast storms, not packets (not trying to be rude, just clarifying that)