I understand that most ARP requests are broadcasted to the entire network. What about ARP replies?Are they sent directly to the host asking for the answer? Or must ARP replies go through the router first? From wireshark,it seems like the ARP replies go directly to the host making the initial ARP request. However, when I try crafting my own packet and sending an ARP reply directly to another host(without the host asking), my destination MAC gets changed automatically to that of the router instead of the MAC of the host I specified.

closed as off-topic by Ron Maupin Feb 7 at 0:12

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  • "I am trying to force an ARP entry into another host but that host is not receiving the ARP replies. It seems like there is some sort of protection against ARPspoofing." Unfortunately, questions about bypassing network security or policies are explicitlyoff-topic here. Also, switches can be configured to do things like DHCP Snooping and Dynamic ARP Inspection, etc. to prevent spoofing. – Ron Maupin Feb 7 at 0:12

Perhaps I have misunderstood however- The broadcast domain for a ARP the boundary of the switched network of which each router is a boundary point. So yes replies go direct , no they do not and cannot go through a router . However a router will send a response to a Arp request for an IP address that it has. A proxy arp function exists for some routers and this may be relevant to what you have seen. I'm not sure why the router would change a ARP reply from someone else but without seeing what the data and routing layout I can't be sure what is happening.

Are you trying to force a ARP entry into the ARP table or a device ? Or perhaps you are trying to give an IP address to a device by broadcasting a ARP packet , I remember doing this for some printer servers. I cannot remember the exact details again however the source of the ARP packet it must be on the switched network.

  • I am trying to force an ARP entry into another host but that host is not receiving the ARP replies. It seems like there is some sort of protection against ARPspoofing. Where can the protection be enforced, at the switch level perhaps? – Lew Wei Hao May 3 '17 at 12:49
  • I've seen a firewall do this but I can't see how a switch could do it would mean the switch sees the Arp requests and then allows an ARP reply. I'd guess any such anti Arp spoof is inside the requesting device. That is if it did not send a ARP request then it will not add the ARP reply to its ARP table. – Ross May 3 '17 at 22:27

ARP replies are unicast, so only sent to the requestor.

These links may assist:


ARP Replies can they be Broadcast

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