Spanning Tree BID Tie Question
Wigz
Registered Users Posts: 2 ■□□□□□□□□□
in CCNA & CCENT
Hi Everyone,
I recently started studying for the ICND2 exam and have checked in on this forum from time to time. I always enjoy the people/answers. So I've decided to make a post and get more involved with the community here.
I just finished studying STP. As you know STP uses these 4 conditions when making decisions.
1. Lowest Root Bridge ID
2. Lowest cost path to Root Switch
3. Lowest sender Bridge ID
4. Lowest sender Port ID
My question is this - In what real world scenario would the Bridge ID's of 2 sending switches tie?
The BID is a combination of the Switch's priority and MAC address so let's say both switches send a BPDU and have a default priority of 32768, if the MAC address is unique how could they ever tie?
How would I see 32768.aaaa.aaaa.aaaa on SW1 and 32768.aaaa.aaaa.aaaa on SW3? The only thing I could think of was some kind of switch virtualization software, and I am not even sure if that exists.
If this is really easy I apologize,
Thanks for any and all help.
I recently started studying for the ICND2 exam and have checked in on this forum from time to time. I always enjoy the people/answers. So I've decided to make a post and get more involved with the community here.
I just finished studying STP. As you know STP uses these 4 conditions when making decisions.
1. Lowest Root Bridge ID
2. Lowest cost path to Root Switch
3. Lowest sender Bridge ID
4. Lowest sender Port ID
My question is this - In what real world scenario would the Bridge ID's of 2 sending switches tie?
The BID is a combination of the Switch's priority and MAC address so let's say both switches send a BPDU and have a default priority of 32768, if the MAC address is unique how could they ever tie?
How would I see 32768.aaaa.aaaa.aaaa on SW1 and 32768.aaaa.aaaa.aaaa on SW3? The only thing I could think of was some kind of switch virtualization software, and I am not even sure if that exists.
If this is really easy I apologize,
Thanks for any and all help.
Comments
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networker050184
Mod Posts: 11,962 Mod
If two switches have two parallel links between them than the bridge ID will be the same on both links. One of them has to be picked.An expert is a man who has made all the mistakes which can be made. -
Wigz
Registered Users Posts: 2 ■□□□□□□□□□
Oh wow, that didn't even cross my mind. All the diagrams I have been studying show 3 switches with 1 connection between each.
Thanks! -
networker050184
Mod Posts: 11,962 Mod
Somtimes we get so caught up in the technical part we forget about the simple things!An expert is a man who has made all the mistakes which can be made.