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Community Member

Two Switches with same MAC+Priority running STP

Hi

what will happen if two switch with same MAC-ADDRESS and same STP priority will run STP , how will elect to the root bridge ???? how the STP process will handle this situation?

thanx

4 REPLIES
Community Member

Re: Two Switches with same MAC+Priority running STP

Hi Yaniv,

I think STP will determine Root Bridge according to the port (uplink port) ID if the Priority and mac address are equal.

Community Member

Re: Two Switches with same MAC+Priority running STP

thanx for the answer but...

if the switches share the same mac-address so all their ports will have the same port-id or port mac-address..?

i know that in OSPF case when 2 or more routers have the same router-id the process stuck .. is it true to spanning tree?

Green

Re: Two Switches with same MAC+Priority running STP

Well, first off, no two switches (or switchports) will have the same MAC (if they do, you're buying switches from the wrong, very bad place).

Every port of the switch will have (at least) one MAC of it's own.

Given the same priority for all switches/bridges on the LAN, the lowest switch/bridge MAC on the LAN will win as the root.

VLANS take on the MAC of the administrative interface ("CPU"): i.e., xxxx.xxxx.5000, the first port (i.e., fa0/1) is xxxx.xxxx.5001, the second (fa0/2) is xxx.xxxx.5002, and so on

If you do a "show interface", the MAC / bia is displayed in the second line.

Good Luck

Scott

Community Member

Re: Two Switches with same MAC+Priority running STP

thanx scott ..

i know the SPT process.. the thing is that i saw in cisco switches that i can change the MAC-ADDRESS of the switch..

any way i checked it allready and the PROCESS get stuck and no root bridge is elect and all the ports of both switches are stuck in listerning mode.. exepct the ones that configure with port-fast

anyway thanx u all ...

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