Why in ARP request does the source computer broadcast a message with the destination IP address to find the MAC address of the destination computer? Why doesn't it send the message to the default gate way from the beginning so that router can send it to the destination computer?
I think it will make the network less crowded!
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2 Answers
ARP determines the corresponding MAC address for an IPv4 address in the local network (on-link). There's no gateway involved. Since ARP information is cached, there isn't actually that much ARP traffic.
IP is designed on the premise that local node-to-node communication doesn't need any central service - it "just works".
Also, sending to the default gateway would require knowing its MAC address beforehand, and the router would require some mechanism to learn the requested MAC as well.
Since broadcasts are generally inefficient - they prompt every node to examine the packet - IPv6 has moved to using multicast for NDP and in general.
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In the first paragraph you said, "There's no gateway involved." Isn't there a default gateway in every local network?– TruthMay 10, 2021 at 7:28
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1A gateway is a gateway. It can be used as a default gateway when it forwards to all external networks. No, not every local network has a gateway - some networks aren't routed and there's no gateway (e.g. my SAN isn't routed). Also, multiple gateways are possible, even default ones.– Zac67 ♦May 10, 2021 at 7:45
When the destination computer is in the Source computer Network it broadcast the destination IP. But if the Destination IP does not in Source IP Network then the Source computer knows the Gateway ARP and does not send ARP request again.
