MAC address flooding and learning

[sophiya]

1. IP source L3
2. IP destination L3
3. MAC source L2
4. MAC (Layer 2) destination L2

IP is layer 3 source address, MAC is layer 2 source address.
R1# show interface fa0/0

1. IP source = 192.168.0.1
2. IP destination = 192.168.0.100
3. MAC source = R1 MAC
4. MAC (Layer 2) destination 0000.0000.0000 (FFFF.FFFF.FFFF)

Switch receives this frame, it doesn't care about 1 and 2 (Layer 3), it works with 3 and 4 (Layer 2)
It can see where the Ping came from, and what was the port.

R1# clear ARP
R1# ping 192.168.0.100

CLEAR ARP = deleting all ARP cash

R1# debug
(debugging)
Debugging is a methodical process of finding and reducing the number of bugs, or defects, in a (HERE:packet) computer program or a piece of electronic hardware, thus making it behave as expected. Debugging tends to be harder when various subsystems are tightly coupled, as changes in one may cause bugs to emerge in another.
DEBUG command is for looking for more details what is going on.

R1# show IP ARP
R1# conf t
R1# no service timesteps
R1# end

R1#int f0/0
R1# no shutdown
Every time you shut down the enterface, it resets the processing.
Switch receives this frame, they know IP but doesn't know MAC address. SW floods it to every interface it does have.

IP sent req
IP ARP rcvd rep src (receiver reply) what is the MAC address
And so SW learns sMAC addresses, and for eg.  R1 has MAC (AAAA.AAAA.AAAA) at Fa 0/1