From BSCM study guide. Spanning Tree bridgin' loop

[rcasta]

Hello,

After reading a bit BCMSN (Building Cisco Multilayer Switched Networks), I was presented with the following diagram:

Switch Block 1 Switch Block 2
Access Sw1 Access Sw2 Access Sw1 Access Sw2
... ...
Access Swn Access Swn Access Swn Access Swn
| | | |
| | | |
Distrubution Sw1 Dist Sw2 DistSw1 DistSw2
| | | |
| | | |
/ \ / \ / \ /
CORE SW1 CORE SW2


The scenario is quite forward, in both blocks access switches are connected to distrubution switches with redundant uplinks using STP. And distrubition switches are connected to both core switches as to keep redundancy up. Nevertheless, the book says if Core Switches are connected to each other a STP bridging loop might occur.

Can anyone please explain me how could this happen?

Best regards,

 

[routerman]

I read this when studying for my CCNP, and I didnt understand the point either!

When building a switched network my core switches are connected directly together with a high speed L2 link This is the method that the CCDA book describes.
Its inevitable in a design with redundancy that you'll have loops, so its a question of assigning the correct root bridge placement so you dont end up blocking a core link.

I think this is what they meant, just they didnt say so.