Friday, February 28, 2014

IPv6 and Network Auto-Configuration with IPv6

Hello All,

In order to run IPv6 in your network or personal home computer, you need to setup either DHCP server or IPv6 autoconfiguration. Today, I am going to explain IPv6 autoconfiguration in Linux. Autoconfiguration is stateless in the case of IPv6. If you get all configurations through DHCP server, it's going to be stateful. The beauty of stateless IPv6 autoconfiguration is that you don't need any independent server or DHCP server to connect to your network. It's like plug and play.

IPv6 protocol configures a host  automatically and provides all information that a host needs it. In other words, configuration information is integrated into the IPv6 protocol.With IPv4, you have to configure either manually or use DHCP server to provide configuration information. Therefore, hosts with stateless IPv6 are no longer tied to a particualr DHCP server.

Here is how IPv6 autoconfiguration works on a local network:

IPv6 stateless uses MAC Address of NIC card or network adapter to create a temporary address. Note: MAC address is a unique global address for each NIC card.Then it adds a network prefix of FE80:: to MAC address to create a link-local address (IPv4 equivalent of link-local is The link-local prefix is used for physically connected hosts to LAN.

Then, it uses NDP protocol (Neighbor Discovery Protocol) to test the uniqueness of address and make sure that no host is using this address. However, this address is just useable for local network (LAN) and it cannot be routed to a larger network.

If the hosts want to reach larger networks such as Internet, the router provides the larger network address. That network address, provided by router, will replace the original link-local prefix by either a complete global Internet address or unique-local address in case of private network (IPv4 equivalent of unique-local is,,, RFC 1918).
Routers keep advertising this address information and NDP protocol is used to query information. Also, it can be requested specifically.

                                                                             Figure 1

                                                                             Figure 2

In short, a host in IPv6 stateless address autoconfiguration network uses its own MAC address to create a temporary link-local address (FE80:: prefix) to be able to connect to router. Then, the router
sends its network prefix to replace the link-local prefix and create a full Internet address.

Router Renumbering
What will happen for your network and IPv6 autoconfiguration if you change your ISP?
That means that your are changing your network address in IPv6. well, routers renumber/reassign the addresses on their network by RR (Router Renumbering) protocol. The router replaces network prefix with the new one. And similar to DHCP it puts a lease time for network prefix.

And that's it. In the next article,I would like to talk about Linux as an IPv6 Router. Don't miss it.
I hope you enjoyed.
Khosro Taraghi

1 comment:

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