PC1 ----- (P1) SWITCH1 (P2) ----- (P2) SWITCH2 (P1) ----- PC2
- Assume two network switches SWITCH1 and SWITCH2 are interconnected to each other through their ports P2 respectively present on each switch.
- A PC1 is connected to SWITCH1 on port P1 with mac-address aaa.aaa.aaa and an IP address of 10.0.0.1/24. A PC2 is connected to SWITCH2 on port P1 with mac-address bbb.bbb.bbb and IP address 10.0.0.2/24.
I have the following two questions: When PC1 sends an ARP request to determine the mac-address of PC2
- What will be the source mac-address in the "ethernet frame" sent out of port P2 of SWITCH1?
- What will be the source mac-address in the "ethernet frame" sent out of port P1 of SWITCH2?
Assume: Port P1's mac-address on SWITCH1 is ccc.ccc.ccc. Port P2's mac-address on SWITCH1 is ddd.ddd.ddd. Port P1's mac-address on SWITCH2 is eee.eee.eee. Port P2's mac-address on SWITCH2 is ggg.ggg.ggg. SWITCH1 and SWITCH2 are not aware of the mac-addresses of PC1 and PC2 initially and will flood the ethernet frame containing the ARP request packet out all ports except the port on which it was received on.
Please note that I am NOT interested in knowing the Sender and Target hardware addresses inside the ARP request packet sent from PC1 arriving on port P1 of SWITCH2. I am already aware of what those would be.
I am specifically interested in knowing and trying to understand the Ethernet frame make-up sent out of port P2 of SWITCH1 towards SWITCH2 and then out of port P1 of SWITCH2 towards PC2.
Since the original ARP request from PC1 will be a broadcast ethernet frame I am assuming that both switches will simply forward the ethernet frame with the destination mac-address set to fff.fff.fff out all ports except the port that the frame was received on.
Will SWITCH1 simply forward the ethernet frame received from PC1 keeping the source mac-address intact of PC1 or will it change the source mac-address to that of port P2 of SWITCH1 when forwarding the frame our port P2?
Will SWITCH2 simply forward the ethernet frame received from SWITCH1 keeping the source mac-address intact of PC1 or will it change the source mac-address to that of port P1 when forwarding it out of port P1 towards PC1?
If the source mac-address is changed inside the Ethernet frame when sending the frame out of a port the label "forwarding" seems a little misleading since the source mac-address is modified. In that sense then routers truly forward and IP packet keeping both source and destination IP addresses intact.