Now how do you switches learn about each other.
As mentioned bridge protocol data units or BPT use are sent out of all ports on switches by default
every two seconds when running spending three switches will learn about each other when they receive
BPT use from other switches on their ports.
As an example in this typology switch one will know that there's a loop because it's receiving a PPD
from switch to on port 2 as well as Port three.
So BPT use from a switch with the same bridge ID are received on multiple ports and thus switch one
knows that there's a loop between itself and switch to in the same way switch to knows that there's
a loop because it receives BPT use from switch one on both port 1 and port 3.
In other words it's receiving BPT use from the same switch on multiple ports.
Hence they must be a loop.
Now PPD use contain lots of information and I'll demonstrate that in a moment.
One of the pieces of information that a BPT contains is the bridge ID of the sending switch a spending
tree bridge IDs an 8 byte value unique to the switch.
It consists once again of a two by two party field and a six binary system ID with a system id being
based on the burnt in MAC address of the switch.
So in other words the bridge I.D. consists of the property 6:57 6:08 by default in decimal or eight
thousand in hexadecimal and the MAC address of the switch.
That means that the bridge is going to be unique in spending three.
So BPT use contain information about spending tree switches.
S. BPT use using a unique MAC address to a destination multicast address of because 0 1 ADC 2 0 0 0
0 0 0.
Or if using Poovey and spending 3 0 1 0 0 0 0 C C C C C C D.
There are three kinds of people who use a configuration BPU which is used by spending tree to provide
information to switches a topology change PPD you to tell switches of a change and an acknowledgement
PPD which is used to confirm the receipt of a topology change notification are sent by default every
two seconds once again.