Tested: Autoconfiguring IPv6 clients

Detention

Article from ADMIN 05/2011

By Konstantin Agouros

Most clients on a network need both an address and some environmental information such as a name server or a web proxy. This article investigates whether a recent operating system on an IPv6-only LAN can handle this.

The routing and addressing problem is nothing new in the IPv4 world. Version 6 of the Internet Protocol (IP), which is no spring chicken itself, was designed to help. This article investigates whether IPv6 can provide a full-fledged alternative to IPv4 on today's networks. Despite my initial euphoria, reality hit me hard during my testing sessions and turned this article into a report about my own experiments on an IPv6-only network.

The Theory

The method a computer on an IPv6 network uses is described in theory by the Internet Engineering Task Force (IETF). RFC 4861 [1] specifies the Neighbor Discovery Protocol (NDP), which replaces the Address Resolution Protocol (ARP) among other things. It is responsible for mapping MAC addresses to IP addresses but also discovers the router responsible for addresses on other networks and optionally distributes address prefixes for the local network. The sequence is as follows:

When the interface is enabled, a Router Solicitation Request is sent to the multicast address ff02::2 (all routers on the local LAN segment.) All IPv6 routers on the network reply with a Router Advertisement.
Depending on the flags in the advertisement, the client either automatically configures an IP address in the prefix it receives using the MAC address in EUI64 format (see the "Creating Addresses with EUI64" box) or in the anonymizing temporary version [2]. The flag for this is AdvAutonomous.
If the AdvManagedFlag is set, the "administered protocol" is additionally used for autoconfiguration – this means DHCPv6. If both flags are set, the client uses DHCP to retrieve an address and assigns the automatically configured address to itself.

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