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How does ARP know the ip adress of where it needs to look?

asked 2021-01-09 12:34:26 +0000

foggie gravatar image

Hi, I'm only a beginner and ARP is a little confusing, I understand a bit about how ARP works, but I'm very confused how ARP knows what IP address it needs to look for? Especially if the ARP cache is empty? If 1 person wants to send a file to another computer on the same network it needs the MAC and i don't understand how it knows what IP address it needs to ask for the MAC? i hope this makes sense and someone can help.

Many thanks

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answered 2021-01-09 16:38:20 +0000

JasMan gravatar image

The client knows the IP address from the destination path which you have to enter to establish the connection.

Example: you want to send a file from PC1 (192.168.1.10/24) to PC2 (192.168.1.20/24) by using Windows Explorer. You enter the path into the address field (e.g. \PC2\Share) and hit enter. PC1 will now ask his DNS resolver for the IP address of PC2. Your DNS server will answer the request with "PC2 has the IP address 192.168.1.20". Due to his subnet mask PC1 knows that this address is in his subnet, and therefore he will send an ARP request "Hey, who has the IP address 192.168.1.20. Please tell me (192.168.1.10)" to the mac broadcast address ff:ff:ff:ff:ff:ff. Every client in the subnet will receive this request, but only PC2 will (should) answer "Here! It's me! I'm reachable at 11:22:33:44:55:66".

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Thanks very much for your answer, that makes sense to me now and has saved me many hours of endless searching

foggie gravatar imagefoggie ( 2021-01-09 17:04:10 +0000 )edit

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Asked: 2021-01-09 12:34:26 +0000

Seen: 111 times

Last updated: Jan 09