Why am I getting a 169 IP address at startup?

Question

I have several Windows 7 machines on a small network in our testing lab. There is a DHCP server in our environment. All the client machines have obtained valid DCHP IP addresses.

When a machine is rebooted, I have noticed that upon startup, the network interface has a 169.x IP address for a period of time (maybe 10-15 seconds after the adapter comes up) before it gets a valid address again.

Is there a mechanism (maybe in the registry) to prevent one of these automatic IP addresses from being assigned?

Answer 1

You aren't experiencing an error or failure. The IP address assigned to the interface is because of automatic private IP addressing (APIPA). It's used because the DHCP process did not receive a valid usable IP address.

Microsoft offers guidance on automatic IP addressing without DHCP:

How to use automatic TCP/IP addressing without a DHCP server

And from a related bulletin (using APIPA on multiple adapters/routing not working):

Disable APIPA on the Entire Computer

Use Registry Editor to create the following registry key:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters

Add the following value to this key:

Value name: IPAutoconfigurationEnabled Value type: REG_DWORD Value in hexadecimal: 0 (A value of 0 disables APIPA support on this computer)

NOTE: If the IPAutoconfigurationEnabled entry is not present, a default value of 1 is assumed, which indicates that APIPA is enabled.

After you make this change, restart your computer.

Disable APIPA on All but One Network Adapter

Use Registry Editor to create the following registry key, where adapter name is the name of the Dynamic Host Configuration Protocol (DHCP) configured adapter where you want to disable APIPA:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\ Services\Tcpip\Parameters\Interfaces\adapter name

Add the following value to this key:

Value name: IPAutoconfigurationEnabled Value type: REG_DWORD Value in hexadecimal: 0 (A value of 0 disables APIPA support on this adapter)

NOTE: If the IPAutoconfigurationEnabled entry is not present, a default value of 1 is assumed, which indicates that APIPA is enabled.

After you make this change, restart your computer.

Answer 2

My experience with this is:

1. Ran out of IP addresses. DHCP server has issued them all out and has no more available.
2. Default gateway settings being sent out by router is missing, wrong, etc... Basically the clients cannot find the default gateway which means it cannot access the DHCP server.

When someone tells you to assign static you must manually put the gateway and mask in, so then it all of the sudden works. Also, if another client on the network is using that IP address from the DHCP and you set yours to static with the same IP address you will sometimes boot that client's dhcp lease, yours will work and theirs will go down.

If this is the case, check your default gateway broadcast settings on your router. I have had mine set to 0.0.0.0 when I made a change to the DHCP scope. Didn't realize it, so the router was telling all clients that were connecting that their gateway was 0.0.0.0

We have 57 computers on our network and about 100 devices. we have reached the limits of our 255.255.255.0 mask. I saw some weird stuff happen with PCs when IP address start running out and especially when the gateway is being broadcast as 0.0.0.0. I even had a few computers blue screen trying to connect to network.

Answer 3

yes you can disable APIPA on windows.

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters

create D-Word IPAutoconfigurationEnabled should be 0 for disabled 1 for enabled.