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I connect my kubuntu to a network in a dhcp scope where some hosts has manual IP addresses. DHCP offers IP to my client which is conflicting with one of manually configured hosts, kubuntu accepts this conflicting IP address and assigns to NIC. what is the problem? why don't it refuse that ip ?

As I know in DORA procedure which occures in DHCP IP request, after dchp Offers first availible IP address to client, client uses ICMP to know if someone else using that IP in that zone, and if so client refuses use of that IP until DHCP offers a free IP address. so my kubuntu should not accept and use that conflicting IP. why this happens?!

thanks in advance

PS: My DHCP server is a windows server service, if it makes sense anyhow. but no any other windows clients has similar problem!

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Huh? It's the DHCP server's responsibility to make sure that it doesn't offer clients an IP that is already in use.

If it does, that DHCP server is clearly buggy, or (more likely) your network setup is broken. If you have some fixed IPs in your network, make sure to configure your DHCP server to not assign those IPs! This is not the responsibility of each DHCP client.

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  • But I doubt if it is as you mentioned, in enterprise networks, your dhcp server may be placed in some zone that has only dhcp ports open (ie 55, 56, 57), and has no access to send or receive icmp packets for security reasons, so how can it make sure of ip not being used by someone else? I can recall it from years ago that dhcp client Broadcasts R-ARP packets to make sure no one has dhcp offered ip in its zone. BTW my other windows clients has no problem with dhcp so I can hardly tell it's dhcp servers problem
    – Sina
    May 12, 2021 at 12:59
  • The DHCP server is the authority for its range of IPs. It's not begging for leftovers, it is actively assigning them. If any other machine uses an IP of that range without getting a lease from the DHCP server, that's a violation of network protocol. I don't know (neither do I care) what Windows clients do or if they have a mode to support broken network setups. But that's not how this is defined.
    – HuHa
    May 12, 2021 at 13:28

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