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New Member

Question about IP addressing

This popped into my head and I couldn't figure out the answer:

Say you have a LAN that uses the subnet. If Host A on that LAN needs to send a packet to a destination IP, Host A will ARP for it. What is there happens to be a Host B on the local LAN with IP address The ARP request doesn't send out a subnet mask. Won't Host B mistakenly think the ARP request is for it?

Any input is appreciated!

Cisco Employee

Re: Question about IP addressing

Hi Chris,

Yes the host B will reply to the ARP request and they will be able to communicate with each other.



Hall of Fame Super Silver

Re: Question about IP addressing


Ankur's answer is correct. But I would like to go a bit deeper into the question and give a slightly different answer. The question suggests that there is a host with and also Host B with That is a serious problem in the network because now there are 2 hosts with duplicated IP address (the fact that they have different masks does not make them different addresses). If there are 2 hosts with the same IP address, then both hosts will respond to the ARP request and Host A will choose one of the responses and use that MAC address. It is therefore unpredictable which of the hosts will actually receive the IP packets.

It is a cardinal rule of IP networking that there should not be duplicated host addressing within the network. This question violates that principle.