Ccna routing and Switching Complete Study Guide

Automatic Private IP Addressing (APIPA)

Okay, so what happens if you have a few hosts connected together with a switch or hub 

and you don’t have a DHCP server? You can add IP information by hand, known as static 

IP addressing, but later Windows operating systems provide a feature called Automatic 

Private IP Addressing (APIPA). With APIPA, clients can automatically self-configure an 

IP address and subnet mask—basic IP information that hosts use to communicate—when 

a DHCP server isn’t available. The IP address range for APIPA is 169.254.0.1 through 

169.254.255.254. The client also configures itself with a default Class B subnet mask of 

255.255.0.0.

But when you’re in your corporate network working and you have a DHCP server run-

ning, and your host shows that it’s using this IP address range, it means that either your 

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TCP/IP and the DoD Model 

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DHCP client on the host is not working or the server is down or can’t be reached due to 

some network issue. Believe me—I don’t know anyone who’s seen a host in this address 

range and has been happy about it!

Now, let’s take a look at the Transport layer, or what the DoD calls the Host-to-Host 

layer.