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What is Automatic Private IP Addressing (APIPA)?

Generally, in today’s world of technology we know that the 169.254.xx.xx is a junk IP on a client 
device which fails to attain an IP address, but what we do not understand is how and why this 
happens and  what is the terminology used to describe this.

Today, I’m talking about this Automatic Private IP Addressing or APIPA as it is commonly called.

APIPA is a term used for auto assigning of the IP address to the LAN and WLAN interface on a  
Windows Operating System when it can’t reach the DHCP server. It is important to understand 
that in order for any device to be a part of the network, it needs an IP address and when this is 
not possible, the APIPA allows the LAN or WLAN interface to assign itself a unique IP address.
As seen above, Network connection 1 indicates a normal working setup wherein the DHCP server 
is Enabled on the router and all the client devices acquire IP addresses in the range 192.168.0.xx 
(xx ranges from 2 till 254) with the default gateway 192.168.0.1 and subnet mask 255.255.255.0.

The network connection 2 shows the condition under which the APIPA comes into effect. Since 
the DHCP server on the router is disabled, all the client devices fail to obtain an IP address. The 
Windows clients then use the APIPA function to auto assign itself with the IP address 169.254.0.1
through 169.254.255.254 with no default gateway and class B subnet mask 255.255.0.0. 
 
These unique IP addresses are reserved for APIPA purpose ranging from 169.254.0.1 through 
169.254.255.254 with default Class B subnet 255.255.0.0. This helps troubleshooting on the network. 
APIPA is auto enabled on all the DHCP client devices and can be configured to any desired private 
IP address but this violates its purpose. APIPA also keeps checking for the availability of the DHCP 
server after particular interval. Once it detects a DHCP server, it configures the client device with the 
dynamic IP address from DHCP server.

I believe this post might have been an informative one. So keep visiting for more in the days to come.

Comments

  1. Anonymous28 April 2018 at 17:34

    That's very simplified explanation. Easily understandable...

    ReplyDelete

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