network cisco ccna gns3 certification arteq

network cisco ccna gns3 certification arteq
a network runs through it

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Sunday, January 8, 2012


note the simple switch diagram...

all switches have a priority of 32768, the default
sw1 is root because it breaks the tie with the lowest bridge id of 1111.0000.0000
sw2 is 2222.0000.0000 and sw3 is 3333.0000.0000
sw1 is root, cost is zero to itself and therefore has all ports designated, it doesn't have a root port because it is root
bandwidth is fastethernet which makes the cost of each link 19 directly to the root, whereas sw2 and sw3 using their common segment to get to the root would have an aggregate cost of 38 each way to sw1
so we have determined the root ports of the non-root switches which means designated (forwarding)
now the question is which port is blocking on sw2 or sw3?

the bridge id breaks the tie, sw3's non root port is placed in blocking state

if the link from sw1 to sw3 was changed to 10Mbps, sw1's port to sw3 is still designated because all ports on the root switch are forwarding but the path from sw3 to sw1 is faster via sw2 now... so sw3's port to sw1 is blocking...

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