200 vs 301

200 vs 301.This section reviews the rules of STP, while highlighting several important troubleshooting points. This section also describes in particular the arbitration rules that STP uses to make decisions for use in depth. It also provides some practical advice on how to answer questions on the exam, such as "Which switch is the root switch."Determining the Root SwitchDetermining the STP root switch is easy if you know the BIDs of all the switches: just choose the smallest value. If the priority and MAC address are listed separately in the question (which is common in some show command output), select the switch with the lowest priority, or when the same priority exists, select the lower MAC address value.To put it in perspective, STP neither has nor needs any additional arbitration rules for electing the root switch. the BID takes the switch's common MAC address as its last 48 bits. These MAC addresses are unique, so there are never identical BIDs, and no additional "arbitration rules" are needed.On the exam, questions about the root switch may not be as simple as listing a number of BIDs and asking you which one is the "best". There may be a simulated environment type question that must be solved using several show commands, or it may be a multiple choice question that lists the output of one or two commands and then asks you to compute the rest using the STP algorithm.When faced with a test question that uses a simulated environment or just provides output like this, you can use a simple one like exclude switch40 Chapter 2 Configuring Spanning Tree Protocol (STP )SW2# showspanning-tree vlan 20rootVlan Root ID Cost Hello Max Fwd Time Age Dly heart t PortVLAN0020 32788 1833.9d7b .0e80 | SW2# show spanning-tree rlan 20 VLAN0020 Spanning tree enabled protocol ieee Root ID Priority 32788 Address 1833.9 d7b.0e80 Cost 4 Port 26 (GigabitEthernetO/2; Hello Time 2 sec Max Age 20 sec Bridge ID Priority 32788 (priority 32768 Address 1833.9d7b.1380 Hello Time 2 sec Max Age 20 sec Aging Time 15 sec Interface Sts Cos | Prio.Nbr 2 2015 Ml Forward Delay 15 sec sys-ic -ext 20) Forward Delay 15 sec Type