IPv4 Link LocalTags:
To participate in wide-area IP networking, a host needs to be configured with IP addresses for its interfaces, either manually by the user or automatically from a source on the network such as a Dynamic Host Configuration Protocol (DHCP) server. Unfortunately, such address configuration information may not always be available. It is therefore beneficial for a host to be able to depend on a useful subset of IP networking functions even when no address configuration is available.
It means link-local address are used when host is not able to get any network configuration from
- Manual Configuration
- DHCP (DHCPv4 or DHCPv6)
then it automatically take IP from pool of
169.254.0.0/16 (169.254.0.0 – 169.254.255.255)
mentioned in RFC 3927
- Take any random IP from above pool
- Check if IP is not taken by others using broadcast via ARP
- If IP is taken then go back to step 1
- If IP is not taken, then assign the IP to yourself and be ready for networking.
Important points to be noted
- These address are not routable by router
- Why : Because it’s in RFC, our rulebook for internet and also rule makes sense too.
- In step2, we only check in our ARP domain i.e. layer 2, it makes sense not to get these routed by layer3, since there is bright chance other machines in their layer 2 would’ve done the same and IP would conflict.
- RFC 3927