My question is, when a Cisco switch participates in STP for the root
switch election, and makes a BPDU with a MAC address in it, where do
they get that MAC address? Do they just pick one of the MAC addresses
from a random port inside themselves? Is it an unused port they pick?
Otherwise, what if that port needs to use it's address for its own BPDU?
Thanks for any info...
DavidH
Correct Answer by farroar on Jun 12, 2010 8:40 PM
farroar
If you were to look at the frames being sent in an STP election process you would see that the source MAC address would be of the port that the frame was exiting and the destination would be a multicast addresses used for STP.
Inside the frame the BPDU packet would list the switch's priority as well as it's base MAC address for the election. The base MAC address represents the switch where as the switchport MAC addresses represent the ports only. Each switch will use it's base MAC address for the election process. You can find out a switch's base MAC address by using the show version command.
Hope that clears it up for you!
Отсюда
DavidH
Correct Answer by farroar on Jun 12, 2010 8:40 PM
farroar
If you were to look at the frames being sent in an STP election process you would see that the source MAC address would be of the port that the frame was exiting and the destination would be a multicast addresses used for STP.
Inside the frame the BPDU packet would list the switch's priority as well as it's base MAC address for the election. The base MAC address represents the switch where as the switchport MAC addresses represent the ports only. Each switch will use it's base MAC address for the election process. You can find out a switch's base MAC address by using the show version command.
Hope that clears it up for you!
Отсюда
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