Duplicate IPs

Recently as well as in the not so recent past I have noticed that certain devices like the IP phones complain or stop working when a duplicate IP is detected. This also seems to happen ever so often with game consoles (since they are connected to the network too).

Aside from this being quite annoying I was wondering how I can solve this issue once and for all.

Would changing the settings in DNS so dynamic updates are changed from just secure to both secure and non-secure do anything to help this matter or am I looking at the wrong thing.

I have tried removing IP addresses from DHCP in the hopes of resolving the conflicts, but still some seem to stick around and cause certain devices to not work until I can find the old device that was using the IP or simply set the non-functioning device to a static IP.

Perhaps the solution is right under my nose, but I am not sure what I need to change in order to get this problem out of my way permanently.

As always thanks for any light you can shed on my problem.

DNS is not what you are wanting. DNS is for resolving host names to IP addresses and wouldn't fix your problem with duplicate IP's. It is most likely a problem with your router. Do you have DHCP turned on for everything or are you statically assigning addresses to some of your devices? Sometimes when you do this, DHCP in your router(or server) might not notice that ip is taken and assign it to something else causing this conflict. If you are using static ip's for some things, set everything to DHCP and that should fix your problem.

Hope this helps a little

The only router we have is the one connecting us to the internet. Everything else is on a lot of switches.

If a device keeps trying to take an occupied address how can I have it re-request an different IP address? Or is that even possible.

Everything except for a few machines, servers and consoles are on DHCP. The range of IP address is very large though so I don't get why the devices don't just grab the next availible IP. Any ideas?

Thanks for the info.

A network card will always try to use the last ip address issued to it. In dhcp you can set detection conflict (ping first to see if the address is in use) in windows dchp its on the dhcp server name under properties and advanced.

I always follow the following plan when addressing a network


.1-.10 = Network edge equipment
.15-.40 = Servers
.35-80 = Printers
.100-200 = DHCP Scope for Workstations

Another thing to consider is that you have only one DHCP Server on your network, if you have a Server make sure you use it's DHCP and turn off the DHCP on the Router.

do you have enough addresses in your dhcp range? Check the expiry too, we've had the dhcp set not to expire. Found a device that was thrown away three years ago in the dhcp. eugh.

This most recent duplicate IP was caused by two phones fighting over the same IP. I just had to track down the MAC address and tada found the issue reset that phone and it worked again.


Damn VOIP...I liked it better when I plugged the damn phone into a wall and it worked...now these things have to load up before you can use them.

what IP are tyou getting ?

if it's the 169.254.x.x
then you do't have DHCP enabled
OR
if it is a different set
you might nee to set the DHCP scope correctly
ie, only allow it to set IP's from x.x.x.20 - x.x.x.255, so you can allocate the first 20 to what you need or know

my 2c

try setting the lease to a couple of hours...see if that makes a difference

When you say "Lots of switches" how are they linked? Outside the box idea but if the switch is remembering IP Addresses incorrectly due to change in traffic flow that may cause conflict.

If you want to resolve your conflict issues you can alway statically assign each device. Simply speaking, if you have only 1 DHCP server there is no reason for a conflict except maybe where DHCP does not notice a static device and uses same address [mungyun](but this should auto resolve).

I would imagine the VoIP phones will need a DHCP server and i believe it would be the VoIP gateway doing this. You would also have a server with DHCP for your computer workstations. By any chance is the VoIP System on the same subnet as your data network?

if so i would separate this as there is absolutely no need and is common sense to have them logically separated.

CTO

What kind of router? Is the router the one handing out DHCP addresses?

Tim

I have had the same problem in my experience certain devices like terminals do not register correctly in DHCP or do not release their lease quick enough - So then another machine try using that IP and causing a conflict I sometimes have issolate IP's from the scope as Foxloxley suggested.

We have also set the lease down to a couples of hours instead of 24