CyberCertPrepNetwork FundamentalsNetwork DevicesEASYFree question
What is the role of ARP in a basic LAN communication, and why does a PC need to ARP before sending its first packet?
- A.ARP is performed by the switch automatically - the PC doesn't need to ARP; unmanaged switches support SNMP, port mirroring, and VLAN trunking out of the box. Hardware redundancy in chassis switches means each line card holds a full copy of every other card's buffers
- B.ARP is only needed when the destination is on a different subnet
- C.ARP is only needed for internet communication, not local LAN
- D.Before a PC can send an Ethernet frame locally, it needs the destination's MAC address. ARP broadcasts 'who has IP x.x.x.x?' to all hosts. The owner replies with its MAC. The sender then constructs the Ethernet frame with the correct destination MAC
Why D is correct
Ethernet delivery requires MAC addresses. The IP stack knows the destination IP but not the MAC. ARP: PC broadcasts 'who has 192.168.1.5? Tell 192.168.1.10.' The device at .5 replies 'I'm at MAC xx:xx:xx:xx:xx:xx.' The sender caches this in its ARP table and uses the MAC for subsequent frames. For remote destinations, ARP is done for the default gateway's MAC instead.
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