conflict of IP addresses with router

15 Jan 2006
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United Kingdom
I am using windows XP on my main computer and windows 98 on my laptop.

I have a BT voyager wireless router. My main PC is hard wired into the router and the laptop accesses the internet via wireless through the router.

However whenever the laptop is switched on and tries to access the internet it gets the message

' the system has detected a conflict for IP address 192168. etc with the system having hardware address 52:54:00 etc '

At the same time my main XP computer gets the message 'windows system error. There is a conflict with another system on the network'

My ISP, tiscali tells me that when two computers are on the same broadband connection they only use one IP address and it is up to the router to differentiate between the two computers.

Any idea how I can resolve this. Do you think it is a router problem, or is the wrong IP address set in the laptop. I dont know how to change IP addresses.

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How did you set the IP's on your pc's? manually on at least one. Assuming that you ahvnt changed the default DHCP settings on your router, set both pc's to obtain an IP automatically.
I think you are misunderstanding somehwat, both pc's MUST have a differente IP (this is a LOCAL IP not the ip provided by your ISP), you cannot have 2 pc's with the same IP on the same network segment.
Ok, a bit of background for you, as I don't know how much you know.

An ip address is a number that simply uniquely identifies an active component (router, PC) within a network.

Your router is a little special in that it will have 2 ip addresses, because it connects to 2 networks, the first being the Internet itself and the other being the network created by your PCS. The router basically acts a gateway between the two networks.

You will only get an address conflict if you have manually set the same ip address on more than one active component within your network. The router is the only device that requires a static ip. It can then be configured (usually by default) to issue unique ip addresses o the other components.

The default router ip address will be listed in the manual, but presumably, if you set up the router, you already know what this is.

So, find out what the ip address of each PC is. On the Windows 98 machine, Click START>RUN and type WINIPCFG in the box and press ENTER. You will see a box containing various details. Note the ip address.

On the XP machine, click START>RUN and type CMD in the box and press ENTER. In the window that opens, type IPCONFIG and press ENTER. Note the ipaddress.

If any of the 3 addresses are the same, then that's the problem.

Your router has the ability to assign aunique ip address to each other active device connected to it automatically. If you know how to access the router settings, look for a section called DHCP and make sure it is switched on.

On each of the PCs, you need to access the TCP properties of for the appropriate network adaptors and set them to obtain and ipaddress automatically. Open control panel and network (98) or network connections (XP) and select the properties for the appropriate network adaptor. The settings will be under TCP properties. Post back if you can't find them.
I have checked the IP addresses and find that none of them are in conflict ie no 2 the same. The only odd thing is that on my laptop windows 98 system which uses the wireless connection the IP address (as see using WINIPCFG) is 0.

Is that the root of my problem?
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on the winipcfg screen, change the dropdown box, it will default to PPP adapter, which wont have an ip which is why it gives 0
Yes, as you say it does default to PP adapter. But where does that leave me. Is there anything I should reset on the laptop to give it a IP address.

The main router has allocated it an address which I can see in the DHCP table. But this address does not appear in the laptop itself.
Ben, you missed eggies point. WINIPCFG shows details of all adaptors. When the dialog box apears, it defaults to DISPLAYING the PPP adaptor information. Click on the down arrow and select the network adaptor (which should be the only other option unless you have more than one). You will then see the ipaddress information for the network adaptor. Post back when you've got the details. The PPP adaptor hs nothing to do with this problem and always displays zeros, ignore it.
Its very strange. After I checked that the IP address of ppp adapter was in fact 0, I just keyed OK. And for some reason the access to the internet started again.

I have just read your response so I checked the network IP address on the W98 laptop and it reads 192xxxxxxx5. This was the same address that I saw in the routers DHCP table yesterday which I think related to my XP PC.

However, checking the DHCP table now I cannot see 192xxxxxx5 in the list.

Shouldn't the DHCP table display 192xxxxxx5 which is the IP address of my laptop.

Anyway everything is working for the moment.

But what is odd is that last night I could see 192xxxxxx5 in the DHCP table , which I think was for the XP PC but now there is a different address listed for that PC - it is 192xxxxxxx7.

But also listed are two new IP addresses 192xxxxxx3 and 192xxxxxxx4 and against these address are the names of two of my neighbours.

Does that mean that they are using my broadband connection at this moment?

Dont know whether to pursue this any further but if you could cast some light on these happenings it will increase the fount of my knowledge.
If you are using DHCP to automatically assign ip adresses to your PCs, then they could quite possibly get a different ipaddress every time they are switched on. This is controlled by the lease time setting in the routers DHCP control panel.

You've moved on a little now without really trying to resolve the initial problem, unless you have inadvertently changed some settings. Have you determined if any of your kit is using a static IP address?

If your neigbours PCs are being listed by the router, then you have an open network and yes, they are or can use your internet and access your network and files etc... This means that you haven't secured your router in any way. You will need to turn on some form of encryption (WEP/WPA/AES) or MAC filtering to prevent this from happening. It could also be the source of your problem. If one of your neighbours has a static IP address on the same subnet, this could be conflicting with an ipaddress being assigned by the router.

In any case the PPP bit is a red herring, IGNORE IT. You simply haven't configured your setup correctly.
I do not know whether I use static IP addresses. I dont think I do. I have never set any up.

For the moment I will just assume that there has been a conflict with my neighbours IP address.

Now that I know how to look for the IP address in the laptop and know how to reference the IP addresses in the DHCP table I will examine these if the problem happens again. So it will give me a clue as to where the problem is.

Anyway thanks for the education as to how IP addressing works.
Switch on the routers wireless security and you will eliminate your neighbours. (Not literally :LOL: )
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