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We currently have several devices on our network. In the last couple of days, a few of those devices are obtaining IP address in another IP range from an unknown source.

Today I left for about an hour and when I came home my phone would connect to the network but there was no Internet connection. However, I could access Internet from a desktop PC on the same physical network. The issue first appeared on another phone and laptop.

What is the cause and how do I fix it?

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  • Can you post the first 2 IP segments? x.x.y.y (the x ones)? They can help identifying the problem. Also write what they should be.
    – LPChip
    Commented Feb 14, 2016 at 18:24
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    I see this occasionally in corporate networks, it is often a rogue DHCP server running somewhere such as someone incorrectly turned on a service or plugged in their own AP/Router, and it is just responding quicker than the "normal" DHCP server. The other possibility is the devices that are not working are connecting automatically to the wrong SSID, check that they are connected to the correct one, or turn your off and see if an identical SSID shows up. This is rare, but can happen and it can really create havok with a wireless network.
    – acejavelin
    Commented Feb 14, 2016 at 18:32
  • Please verify whether there are any duplicate wireless networks in the vicinity. In that case, your current network setup is no longer secure (or wasn’t secured in the first place), because the password would have to be the same for devices to connect to it. Are you perhaps using a repeater?
    – Daniel B
    Commented Feb 14, 2016 at 18:44

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It sounds like your phone and laptop are connecting to an incorrect nearby wireless access point. In your phone and laptop wireless settings, check to see if thats the case and remove that connection and be sure to set them to automatically connect to your access point.

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  • its still our network name, but when checking the IP address the laptop/phone would have a different IP than say the desktop but on the same network. almost like router has two IP addresses that its giving out
    – cassandra
    Commented Feb 14, 2016 at 18:19
  • You need to clarify your problem. Every device in your home will have a different IP address assigned to it. None of them should ever be the same.
    – Keltari
    Commented Feb 14, 2016 at 18:21
  • If the DHCP server fails (scope is full for example), it will hand out no ip address thus a 169.254 address is handed out.
    – LPChip
    Commented Feb 14, 2016 at 18:25
  • the first 6 numbers are the same, (XXX.XXX. all the same) after that is zero dot (0.) then more numbers. when the device stops working it is displaying a one dot(1.) instead of a zero dot (0.)
    – cassandra
    Commented Feb 14, 2016 at 18:28
  • Are those numbers 169.254.x.x?
    – Keltari
    Commented Feb 14, 2016 at 18:36
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This definitely sounds like there are multiple DHCP servers. Since multiple devices are showing the problem, the issue is not likely to be a single broken device that is using a DHCP client.

Since a phone is known to be an issue for at least one device, the issue appears to affect wireless devices.

With some devices, including newer Microsoft Windows versions, you can get some information about the DHCP server that is providing the broken Internet connection. How you do this would vary between different devices. With modern versions of Microsoft Windows, running IPConfig /ALL wills how a "DHCP Server" address. Then, that IP address (e.g. 192.0.2.1) can be used to look for looked up in the ARP table by running "arp -a", which is useful for providing the MAC-48 address. The first six hexadecimal digits (ignore any other characters like colons or hyphens or periods) of the MAC-48 address is the OUI. Using the MAC address lookup @ Coffer (or the information can be retrieved from the more official source, IEEE's OUI.txt) can be used to figure out who manufactured that device (assuming that people haven't been making manual changes to a MAC-48 address).

If you confirm that the DHCP server is not equipment that belongs to you, then you need to sever the connection that causes your equipment to contact the DHCP server. In the case of wireless connections, the typical approach is to tell your own equipment to not automatically connect to certain devices, like unsecured devices. Then you shouldn't be able to connect to that device unless you enter its password (unless you somehow have its password saved, which seems quite unlikely, but even that situation could be fixed by erasing the saved password).

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