which is best election to choose root bridge ? i have topology

[Dr.X]

hi ,

i  have a toplogy as below :

http://www13.0zz0.com/2014/08/17/12/125759738.png

im wondering which is the best choice to root bride ?

is it Core-1 switch at the top ??

or

distribution-2 switch in the middle of the network ??

note that core 1 is the highestperformance , and the distribution-2 switch lower performancr thatn core1 .

but here im asking 

which is better to elect the root bridge ?

regards

[Furose M]

I dont see a topology attached, but, if your network is layer 2 all the way up to the core, then its better to have the core as the root bridge so that all the other devices could build a shortest path to the core.

[Dr.X]

hi , its layer 2

plz look here

http://www13.0zz0.com/2014/08/17/12/125759738.png

regards

[Dr.X]

could u see it now ?

[Furose M]

It was blocked by Websense. alright.. i see this and for this topology, keeping core as the Root is the best option.

[Dr.X]

can you tell me why ??

is it because better hardware ?

why not distribution-2 ???

i found below :

""Ideally the Root Bridge is as closest as possible to all access (edge) switches to minimize frame travel time"""

???????????????????

[Furose M]

not because it has better performance. if you are running RSTP, every bridge is going to generate the BPDU. so, the performance doesnt matter.

if core is the root, every dist will have a ROOT port and ALT port to the core. so, even if 1 port fails, the other one will take over. even if both the links fail, they will converge towards the other dist leading to the core.

if dist-2 is the root, all of its links must be in FWD state.

if you think about upper left triangle,  link3-4, link 7 of dist-2 are designated FWD. link3-4 of core is Root FWD. link 7 of Dist-1 is Root FWD. so, which link would be blocked? the link 1-2. similarly, the link5-6 of dist-3 would be blocked. so, all the traffic from all the devices in the network will go through the dist-2. you wont be usign the link between dist-1, dist-3 to core at all.

[Dr.X]

Thank you