Ip Address Conflict

[sbk]

I have two desktop PC's and my personal laptop. A friend often comes and uses his laptop too. I have assigned a fairly good sized range with my modem and Wireless access point but still get IP conflicts. If I assign IP addresses to the desktops will that help eliminate the problem? I don't understand why it is conflicting when the range assigned is quite high (like 35 numbers).

[Guest Reimar]

I have two desktop PC's and my personal laptop. A friend often comes and uses his laptop too. I have assigned a fairly good sized range with my modem and Wireless access point but still get IP conflicts. If I assign IP addresses to the desktops will that help eliminate the problem? I don't understand why it is conflicting when the range assigned is quite high (like 35 numbers).

Give the desktops fixed IP's and you'll have less problems. But choose for the Desktops an IP somwhere middle between your range, let say if your range is from 192.168.0.5 til 40 chosss some like 192.168.1.20 and 21 or so!

[sbk]

What should I assign as the DNS then?

I should add that my desktops are plugged into an ethernet switch, as is the wireless access point.

[ungcas]

What should I assign as the DNS then?

I should add that my desktops are plugged into an ethernet switch, as is the wireless access point.

Log on to your Switch and configure the DHCP to assign the IPs based on the Networks cards. This way the same cards will always get the same addresses. You can go into each network card settings and input them manually.

[Guest Reimar]

What should I assign as the DNS then?

I should add that my desktops are plugged into an ethernet switch, as is the wireless access point.

I would use: 208.67.222.222 and 208.67.222.220

That are the DNS server from Open DNS (http://www.opemndns.com) which you can freely use! They may better than the DNS Server from the ISP!

[phazey]

Consult your internet providers for their DNs server addresses, OR use opendns's numbers;

208.67.222.222 and 208.67.220.220

edit: what he said ^

Edited October 18, 2007 by phazey

[jmac]

Make sure you are not running 2 DHCP servers. It sounds like you have a router interfacing your adsl lime going to a switch and your AP connected to that. If you have a DHCP server active in both the router and AP you will have this problem.

[nikster]

If you have this a lot, my best guess would be that you have two DHCP servers running which will cause lots of conflict.

Post a list with all your networking devices here, and access each one of them to check their configuration. Make sure there is only one configured as DHCP server!

For example, you have DSL Router, Wireless access point, and a switch. Then:

- Access all of them and make sure only one is a DHCP server. Let's say you let the DSL router be the DHCP server.

- Make sure all these devices have IP addresses set (fixed) and that the IP address is outside the range of the DHCP server IPs.

- Set the DHCP IP range

Example:

Router 192.168.4.1, set as DHCP server, DHCP server IP range: 192.168.4.30 - 192.168.4.100

Switch 192.168.4.2

Wireless access point 192.168.4.3

You don't need to set your desktops to have fixed IP addresses - they can use DHCP like everyone else. However, if you do want to give them static IP addresses for some reason, make sure to give them addresses outside the DHCP range. Like 192.168.4.4, .5

DNS is completely unrelated to DHCP, there is no need to confuse the issues here. All devices with fixed IPs get 192.168.4.1 as DNS server, all DHCP devices are set to get the DNS server automatically. You can use the OpenDNS servers as mentioned above if you have DNS problems but it's really a different kettle of fish. Get your DHCP server problems sorted first!

Edited October 18, 2007 by nikster

[monty]

I have found one scenario which can generate IP conflicts a lot.

If all IP's are given out by a dhcp server, and you have users around with laptops which are hibernated instead of shut down, they tend to cling onto the IP address they were given before they were hibernated.

An IP which very possible is already assigned to another PC by your dhcp server while they were in hibernation!

I see this quite a lot with regularly returning laptop toting customers, they come in, wake up there laptop and bang, IP conflict somewhere!

I now indeed tend to set ALL devices on my network with fixed IP adresses, and assign a small range to the dhcp server only used by visiting devices. Much less hassle, and when your network starts to grow, it's much easier to keep track of which device is where (I have over 50 networked devices connected now!)

When you set the fixed IP's, you use the same settings as a device would have gotten from a dhcp server, apart from the IP address of course. Normally the gateway and dns servers should be your ADSL router's ip address (or whatever device supplies/distributes the internet).

The opendns servers can be used, but it's much more convenient to set this in the adsl router, then each device on your network will use them as opposed to only the devices in which you changed the dns servers to opendns!

[dsys]

edit - already answered

Edited October 19, 2007 by dsys

[nikster]

I have found one scenario which can generate IP conflicts a lot.

If all IP's are given out by a dhcp server, and you have users around with laptops which are hibernated instead of shut down, they tend to cling onto the IP address they were given before they were hibernated.

An IP which very possible is already assigned to another PC by your dhcp server while they were in hibernation!

Thanks for this explanation - I just had this happen today on my network. I was happily surfing along when all of a sudden, my IP address conflicted with somebody else's. My computer then proceeded to get a new DHCP address and all was fine.

I was wondering about this - why do machines tend to keep their IP address in sleep / hibernate mode? Even if they do, it seems like a poorly designed system if those machines then interrupt others who have done nothing wrong.