Hello all, I've been studying ARP and how switches communicate traffic. Im just getting a little confused with how multiple switches connected in a network determine the destination of a message. I know switches learn mac address and add it to their CAM table, but what confuses me is how do switches know the path to take across multiple switches which is further then just the mac address neighboring devices. Do switches have their own form of routing table I am not aware of?
In this picture after the initial ARP broadcast PC1 learns of PC2's MAC address, how do the switches know which path to route back, and not just broadcast it?
If I could get a bit of information on this I'd appreciate it.
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Your confusion might be because perhaps you don't realize MAC to port address learning doesn't require hosts to be directly connected the switch nor are you limited to only having one known MAC per port.
When a switch receives an ingress frame, on any port, it will note the frame's source MAC was seen on that port.
When a switch receives an ingress frame, if the destination (unicast) MAC is in the MAC table, it will transmit the frame out that port, otherwise it sends the frame to all ports, except the ingress port, within the same broadcast domain.
So, with multiple switches in a path, they work as they normally would. In your example, when PC1 ARP's for PC2, every L2 switch, within the broadcast domain will see the broadcast and record the source MAC and ingress port. I.e. all switch will know which port to use to send to PC1.
PC2's ARP reply, though, will be unicast, so it will flow back across the switch path using the learned PC1's MAC. When PC1 now unicasts to PC2, the switches in the path will have also learned PC2's MAC, from the ARP reply, but unlike the case for PC1's ARP broadcast, all the other switches will not have learned what port to use to get to PC2, but then they don't need to know that either.
If PC1 and PC2 stay active, the switches in the path will keep refreshing their MAC table, but the PC1 MAC learned on the other switches will (usually) soon time out. Like for PC2's MAC, they don't need to know PC1's MAC.
This is actually a pretty cool feature, i didn't even know it existed until I was looking for a solution to advertise a subnet (prefix in BGP talk), only if a certain condition existed. This is exactly what conditional advertisements does
j ai une question j ai achete un routeur cisco 887VA-k9 , je le configuré avec la configuration ci- dessous
si je le lier avec mon pc portable sur l un de ses ports directement ça marche toute est bien ( la connexion internet + m...
Attached policy provides CLI access to the Cisco 4G router over text messaging. Two files are in the attached .tar file:
2. PDF with instructions on how to load and use the .tcl file.