How switch knows mac address

[saishreevj]

When I'm trying to ping from PC1 to PC2, broadcast is sent , PC2 replies. Now Switch learns mac address of source machine PC1, so in the same way it learns mac address of PC2 when it replies to PC1 right?

[balaji.bandi]

Thats right, Switch copy both the MAC address and store them in CAM table, Until the expired time.

[Kasun Bandara]

Hi,

yes. check below video to get good understanding.

https://www.youtube.com/watch?v=TIHvWb-gruc&ab_channel=Networklessons.com

rate this and mark as answer if this resolved your concern

[paul driver · Accepted solution]

Hello
Those PCs are on the same connected network but all devices have no knowledge of each other.

PC1 has a packet to send to PC2, but it doesn’t where to send it, all it knows is it’s own src-mac/ip address and pc2 dest ip  and mac address of 0000.0000.000 so it will arp for pc2 mac address

Switch will check this arp frame and see it’s a broadcast so it will flood it out to all off its ports (minus the one it was received on) and at the same time it will cache PC1 mac-address into its own mac- address table and relate it to the port it was seen on, and when PC2 see it own ip address in this arp request it will unicast replies to pc1 as such the switch caches PC2 mac- address/port also.

Now the switch has knowledge of both PC1/2 source/destination mac-addresses, PC1/PC2 have an arp entry for each other so traffic can now flow between each pc via the switch.

[saishreevj]

@paul driverThanks for the detailed explanation. Its  ff:ff:ff:ff:ff:ff  right, I see you mentioned as 00.00.00.00 for broadcast mac address . 

[paul driver]

Hello
yes i did I was referring to the pc1 knowledge prior to sending a arp request however the broadcast would indeed be ffff.ffff.fffff