Computer networks provide the link-local addresses that can be only used to communicate in the current network segment or broadcast domain in the current network. The Link-Local address is automatically generated by the host and does not needs to get a configuration service like DHCP. The Link-Local Address is automatically assigned by using the stateless address autoconfiguration or link-local address autoconfiguration . This process also known and named as Automatic Private IP Address or APIPA . One of the most prolific features of Link-Local Address is it may no unique in a network and so it is not forwarded by the router in the connected network segment.
Dynamic Configuration of IPv4 Link-Local Address (RFC3927)
One of the most important thing about the Link-Local Address is IP address assignement. As there is no specific help about IP address assignment like DHCP the IP address for the Link-Local Address should be assigned by host itself. the IETF which develops standards about the Internet and related technnologies created the Dynamic Configuration of IPv4 Link-Local Address with the number of RFC3927 .This standard defines different aspects of the Link-Local Address assignment like Applicability, Autoconfiguration Issues, Multiple Interfaces, Shorted timeouts etc.
Link-Local IP Address Range
The Link-Local Address can be selected and assigned from a specific addres range. The Link-Local IP address range is strictly defined in the RFC3927. The address range of the Link-Local IP is 169.254.0.0/16 . This means IP addresses between 169.254.0.0.-169.254.255.255 can be used for Link-Local IP Address. As we can see that there is very long IP address range dedicated to the Link-Local IP Address. As this range is assigned to the Link-Local IP Address do not use this range for regular computer networks where they can not communicate with outside of their current network.
Windows Link-Local IP Address
The Windows operating system can assign and use Link-Local IP address. There is no need extra action as if there is no DHCP server for an network interface after connecting to the network an Link-Local IP Address is automatically assigned to this network interface. We can see the Link-Local IP address by using the ipconfig command with /all option as without this option it is not displayed.
ipconfig /all
From the output, we can see that the Link-Local IP Address is displayed in the Autoconfiguration IPv4 Address line which is 169.254.238.196 which is a random IP address from the 169.254.0.0-169.254.255.255 IP address pool. The Subnet Mask is 255.255.0.0 . As we can see that there is no default gateway as the Link-Local IP Address can not be routed to the outside of the current network.
Ping Link-Local IP Address
The link-local IP address can be used to check network connectivity for the current network by using the ping command. We can ping two hosts which are usig the Link-Local IP Address and located in the same network segment according to the L2. In the following example we ping the Link-Local IP Address 169.254.238.196 .
ping 169.254.238.196