Label the port types ( RP=Root Port, DP=Designated Port, NDP=non-Designated Port) and the STP states (F=Forwarding, B=Blocking) in Figure 6-25. The Bridge IDs are labeled. All links are Fast Ethernet.
Figure A-5 provides the solution for Question 8.
Svr_Farm -Cat-1 becomes the Root Bridge because it has the lowest BID. MDF-Cat-2 and MDF-Cat-3 elect Root Ports based on the lowest Root Cost Path (19 versus 38). IDF-Cat-4 and IDF-Cat-5 have two equal-cost paths (38) to the Root Bridge. Therefore, to elect a Root Port, they have to use Sender BID as a tie breaker. Because MDF-Cat-2 has a lower Sender BID than MDF-Cat-3, both IDF Cats select the link connecting to MDF-Cat-2 as the Root Port. Designated Port elections are all based on Root Path Cost.