Weird Scenario with switching

gbdavidxgbdavidx Member Posts: 840
in CCNA & CCENT
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
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Comments

  • JeanMJeanM Member Posts: 1,117
    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
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  • EdTheLadEdTheLad Member Posts: 2,111 ■■■■□□□□□□
    You need to do some reading on the spanning-tree protocol.
    Networking, sometimes i love it, mostly i hate it.Its all about the $$$$
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  • gbdavidxgbdavidx Member Posts: 840
    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
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  • aftereffectoraftereffector Member Posts: 525 ■■■■□□□□□□
    Sounds like you made yourself a spanning-tree lab.
    CCIE Security - this one might take a while...
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  • gbdavidxgbdavidx Member Posts: 840
    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?
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  • networker050184networker050184 Mod Posts: 11,962 Mod
    What exactly are you trying to fix? This isn't an issue, it's the way STP works.
    An expert is a man who has made all the mistakes which can be made.
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  • Dieg0MDieg0M Member Posts: 861
    If you want to make the light go green just "spanning-tree portfast". Enjoy the meltdown :)
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  • OfWolfAndManOfWolfAndMan Member Posts: 923 ■■■■□□□□□□
    Do you know what the purpose of STP is? Ever heard of a broadcast storm?
    :study:Reading: Lab Books, Ansible Documentation, Python Cookbook 2018 Goals: More Ansible/Python work for Automation, IPSpace Automation Course [X], Build Jenkins Framework for Network Automation []
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  • gbdavidxgbdavidx Member Posts: 840
    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
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  • xnxxnx Member Posts: 464 ■■■□□□□□□□
    No, it's just how STP works, you'll cover it in ICND2
    Getting There ...

    Lab Equipment: Using Cisco CSRs and 4 Switches currently
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  • networker050184networker050184 Mod Posts: 11,962 Mod
    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.
    An expert is a man who has made all the mistakes which can be made.
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  • gbdavidxgbdavidx Member Posts: 840
    thanks!
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  • Jon_CiscoJon_Cisco Member Posts: 1,772 ■■■■■■■■□□
    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.
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  • arrogantbastardarrogantbastard Member Posts: 61 ■■□□□□□□□□
    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)
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