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Cisco spanning-tree and cost question

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  • Cisco spanning-tree and cost question

    Hi all,

    I have a little bit on an issue. First off here is a little network diagram and R1 and R2 are 6509's and SW1-4 are 3560's. R1 is the Root bridge.

    What I want to achieve is using the fibre link from R1 to SW1 as a primary link and if for any reason the R1 to SW1 link goes down, I want it to use the SW4 to R2 link to send/receive traffic.

    On the SW4 g0/3 interface, I have put in spanning-tree cost 300 and the spanning-tree status on it is blocked however when I look at the port, it is green and there is still traffic being received (about 2.5 mbps) however there is very very little traffic going out (like 20 bps). No matter what i try, I cannot get the port to go Amber as it should and have all traffic going out the SW1 link to R1. I have tried port-priority and changing the spanning-tree costs from 25 to 500 as the default cost is 4 on the gb uplinks.

    Anybody have any ideas or comments?


  • #2
    Re: Cisco spanning-tree and cost question

    Do you have different vlans in use?
    Please post the results of "#sh span" of the switches.
    You can use "spanning-tree vlan (vlan-number) root primary" (this is for the root switch R1) and "spanning-tree vlan (vlan-number) root secondary"(this is for the secondary switch R2) to manipulate the root switch. "spanning-tree vlan (vlan-number) priority (priority)" where the default priority is 32768 and the lower is preferred when the selection of the root is in progress. You should decrease the priority in decrement of 4096.
    Last edited by alexbg; 8th March 2010, 08:00.