- Bronze, 100 points or more
hi every body!
i was studying stp and one thing baffled me about bridge id.
bridge id uses mac address and priority
but which mac address is used for bridge id as a switch could have as many mac address as ports it could have ?
any idea about this ?
my second question is about selection of root port on non- root switch.
what happens if a non-root switch receives the two Bpdu with the same root path cost from its two neighbor, assuming non-switch has same path cost configured on the ports BPdu received?
let me explain my question better with example.
assume root port is already elected
switch A is connected to swich B via f0/1 and switch C via f0/2
switch A has path cost of 1 on f0/1,f0/2
swA receives BPDU fron sw B with root pah cost =3 on f0/1. swA receives another BPDU from sw C with the root path cost 3 on f0/2
SWA finds that the cost to reach root switch via f0/1 is
3+1=4 ( add the path cost 1 of f0/1 to the root path cost received in bpdu from sw B)
SWA also finds the cost to reach root switch is
3+1=4 ( add the path cost 1 of f0/2 to the root path cost received in bpdu from sw C)
which port Would swA select as a root port?
The sequence of selection is like this:
lowest priority --> lowest mac-add --> lowest path cost --> lowest port id.
I see your confusion.
The interface MAC address does not play into the Spanning-Tree equation. The switch MAC address does.
As for the other query, yes - you are correct. It's exactly as I stated in my previous post. The lower number port will be preferred when all things being equal.