Same IP on DHCP


(Juan Carlos Fernandez) #1

Same IP can be set it when modifying / creating a reservation on DHCP

(Federico Ballarini) #2

It’s correct in my opinion. By ipconfig /release ipconfig /renew you can renew the IP on the machine that has the old IP. If NS has to verify the IP you can’t reserve an IP if is already assigned to a machine.

It’s not correct if you can reserve the same IP to two different machine.

(Juan Carlos Fernandez) #3

This is what’s happening, you can create/modify an IP Reservation using the same IP (ex. over and over

(Juan Carlos Fernandez) #4

Go to DHCP -> IP Reservation -> Create IP Reservation -> Fill in the info

Go again to DHCP -> IP Reservation -> Create IP Reservation -> Fill in the info and repeat the same IP

It should give some kind of error stating that IP is already reserved, instead this behavior is allowed

This also happen when you modify an IP Reservation and change the IP with another which is already reserved

(Federico Ballarini) #5

Wait! I’ve tried on my server:
If u have machine A and B.

  • If the machine A it’s online and you reserve the same IP for machine B you’ll receive an error
  • If the machine A it’s offline and you reserve the same IP for machine B you can apply this

I don’t know what happen when you put online both, but I think that NS assign the IP to the first machine online and to the second will apply another IP. Can you try to check this?

(Markus Neuberger) #6

dnsmasq supports mapping same IPs or MACs (which may be useful in some cases for example same IP for LAN/wifi).

dnsmasq should act like first come, first served but I never tested.

It’s explained in the dnsmasq manpage, search for --dhcp-host=

(Federico Ballarini) #7

Hi @jfernandez
I’ve checked, the first machine that goes online take the IP reserved from GUI. The others take an IP included in DHCP range, so there isn’t any IP duplication. I think that behavior it’s correct.
How @mrmarkuz was saying, you can assign the same IP to Ethernet Card and Wi-Fi card of one PC, so a check of IP duplication on offline machine will not correct.
If I have solve your problem, you can close this topic.