IPv6 Address Assignment with Stateless Auto-Configuration

by Tony DeSimone

The debate over the pros and cons of transitioning to IPv6 continues. Recent articles have agreed that many organizations are IPv6 capable, but because of NAT (Network address translation) borrowing us time against running out of available IP addresses, and the cost associated with upgrading providers’ hardware being a deterrent, IPv6 isn’t as widely used as some experts thought it may be at this time. In any case, it still seems safe to say that IPv6 is an inevitability.

What is IPv6 stateless auto-configuration?

One aspect of IPv6 that seems intriguing is the stateless auto-configuration. IPv6 stateless auto-configuration is a quick-and-easy, plug-and-play method of having a host join an existing IPv6 network.  Stateless auto-configuration process consists of the following:

The IPv6 host generates a link-local address for its interface. A link-local address is formed by taking the well-known link-local prefix of fe80:: and appending an interface identifier. The interface identifier is derived from the host’s MAC address. This link-local address is used solely on the host’s segment and is not routable. An example of a link-local address – fe80::21b:63ff:feab:e6a6 where 21b:63ff:feab:e6a6 was derived from the host’s MAC address using the EUI-64 interface id assignment.

The link-local address is created so the host can use it to send a Router solicitation message to the all-routers multicast group on its local segment, requesting a router inform the host on what network (prefix) it resides.

In response to its Router solicitation request, the host receives a Router Advertisement (RA) containing the prefix. The host creates its IPv6 address by appending its interface identifier to the prefix. An example of a host’s IPv6 address –2001:DB8::212:7FFF:FEEB:6B40 where 212:7FFF:FEEB:6B40 was derived from the host’s MAC address using the EUI-64 interface id assignment.

Stateless auto-configuration is not a replacement for DHCP (Dynamic Host Configuration Protocol). DHCPv6 will still be used when hosts require addresses for NTP servers, TFTP servers, and other common options. DHCPv6 also offers the audit, tracking and management capabilities if more control of address assignment is required.

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