. Explain the process of election of Route Bridge and criteria that are considered?

selection of route bridge can be done by some following process;

*  selection of bridge id = priority + MAC address

explanation:

suppose you have 4 switches , and all the switches are connected together will the help of cross over cable.  and u need to find the root bridge out of this switches how u can do?

in this case, u need to type the command inside the switch individually, like this:

 for all SWITCH  do same command:   open CLI command in selected switch and  type this command  ,i,e,

switch> enable

switch# show spanning-tree vlan 1     // why should i type vlan1  ? (because initially all the switches defaultly set is in vlan 1 mode, so we writing as vlan 1.)

after writing 2nd command( i,e, privilege mode)  u will get ,info about spanning-tree and root bridge and its related mac address and priority,, here we are finding the root bridge id, so that we need to see only root bridge id info ( i,e, in that note down  priority and mac address only in some where ) 

  In 1st switch ,suppose u will get like this : priority=32769 , mac address= 0001.01DF.25E9.12EF

 In 2nd switch, suppose u will get like this : priority=32769 , mac address=0020.12AC.AEF1.675D

 In 3rd switch, suppose u will get like this : priority=32769 , mac address=0003.56EF.ADC2.75DE

 In 4th switch, suppose u will get like this : priority=32769 , mac address=0001.02DB.15EF.1A2F

See here, in all switches ,priority is same ,so that we are not able to decide that which one is my root bridge, so in dis case we need to check the MAC address of all individual switches and co-relate with each others and manually you need to found that which is LEAST mac address, those switches is having LEAST VALUE( including priority + mac address) , that one act as ROOT BRIDGE .

remember that, first u need to check the priority of all switches, those who is having least priority that one act as a ROOT BRIDGE,

if priority is equal in all switches then we need to check the MAC address, otherwise no need to check the mac address..

so, that as per given example, switch 1 is acting as "ROOT BRIDGE ID" ..

after finding the root bridge id, remaining switches(2,3,4) performing different operation may be it will act as as designation or non-designation port and root port.

for finding the "ROOT PORT",you need to check the "STP COST" in all remaining switches(2,3,4)

SUPPOSE , if all the remaining switches is having same "STP COST( bandwidth )" then, manually (by seeing with eye) we need to check that which switch is cover the shortest path to reach the root bridge, then that one is act as a root port..

for finding of " NDP (non-designation port)  and DP (designation port) " : we have criteria ;

1) priority      2) mac address

those who is having less priority that one act as a DP and other one is act as a NDP..

if priority is equal then cross check mac address.. those is having less mac address that one is act as a DP and other one act as NDP.

***still if u have any confusion then text me comment in text box.. i will late u know.