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Basic STP question

Root Bridge

|

| 1gb

|

Switch 1 - priority 2000, MAC 00.00.00.00.00.11

| PID-fa0/1 .............| PID-fa0/2

| 100mb .................| 100mb

| PID-fa0/2 .............| PID-fa0/1

Switch 2 - priority 2000, MAC – 00.00.00.00.00.22

Root Bridge is already selected; I have two switches below the root bridge.

Switch 1 is with priority set to 2000 and lower MAC address (.11) lower than switch 2.

Switch 2 is with priority set to 2000 (both switch 1 and 2 has same priority), and it has higher MAC (.22) than switch 1.

Both switches 1 and 2 has two parallel links between them, both are of same cost (100mb).

I am confused which will be the RP for switch 2 here. How will take the decision to block one of the parallel links, how will block where? Consider that cost is same for both links, but BID and port IDs are different. They have apposite Port IDs for each link.

I guess both switches will try to block their own fa0/2 because of its higher port ID, cost is same for links, but this will end up with complete blocking because higher PID interface is connected to the lower PID interface on apposite side.

Can any one explain it; this will help in making fundamental clear.

1 REPLY

Re: Basic STP question

Hey Kapish,

Your answer is ready in lan switch and routing forum.

HTH

ANkur

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