How does a device get an IPv6 address?

 Discover IPv6
Nov 042011
 

Spend 30 minutes with IPv6 every Friday!I think all of you have understood that the IPv6 address is both longer and different than the IPv4 address. But how do you enumerate your network? Today, it’s time to understand the basics of IPv6 addressing. 30 minutes will teach you a lot about IPv6 addressing on your devices.

In IPv4, you have many ways of getting an IP address. There’s manual configuration, where you enter the IP address, the network mask and the router address in your system. In addition you can use automatic configuration with DHCP.  If there’s no network configuration,  the system allocates link-local (Zeroconf) addresses automatically.

Like IPv4, but with multiple addresses on each interface

Computer connected to an IPv6 network. So what’s different in IPv6? Nothing really. The main difference is that each network interface will have multiple IP addresses and that we have a few different systems for automatic configuration.

  • Manual configuration is still possible.
  • Automatic configuration is supported by both good old DHCP (now called DHCP6) and stateless automatic configurations
  • Link-local addresses exist alongside the other addresses
Remember now that IPv6 was created a long time ago. At that time, Novell Netware and other LAN systems had automatic configuration of addresses, something that was needed in the new IP network. Like in Netware, IPv6 got automatic configuration of IP addresses based on the MAC – the network card – address. In the Internet age we live in, it might be considered a bad idea to send your computer’s unique identifier – the network card address – to every Internet site you communicate with. As an alternative, your system can use a random number, called a temporary address. Windows does this by default. In OS/X Lion it’s not possible to configure this by default in the user interface, even though the base system supports it. For privacy reasons, I would recommend that all systems use these types of addresses by default.

Example interface configuration

Here’s the network configuration on a typical computer:
en0: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
 ether e4:ce:8f:00:93:3e 
 inet6 fe80::e6ce:8fff:fe00:953e%en0 prefixlen 64 scopeid 0x4 
 inet 192.168.0.24 netmask 0xffffff00 broadcast 192.168.0.255
 inet6 2001:db8:1f15:d79:e6ce:8fff:fe00:933e prefixlen 64 autoconf
 inet6 2001:db8:1f15:d79:1511:ed4a:b5bc:4420 prefixlen 64 autoconf temporary
 media: autoselect
 status: active

The first IPv6 address that starts with fe80:: is the link-local address that exists on all systems that has IPv6 enabled – regardless if there’s any outside connectivity or not. This system has both an MAC-address based IPv6 address and one “temporary” that hides the network card identifier. Applications should select this address before using the other one. As you see, there’s only one IPv4 address on this interface. The link-local address was replaced by an address managed by DHCP. In IPv6, the computer will keep the link-local address.

There is of course a lot of more details about addressing – but to summarize:
  • Every computer always has multiple IPv6 addresses
  • You can continue to use DHCP and static (manual) addressing as before
  • Many devices (heard about the Internet of Things?) will have automatically configured addresses based on the MAC address and the assistance of your router
  • You should consider using temporary addresses, not traceable to a specific hardware
Now it’s time to use the rest of your 30 minutes to learn more. Here’s some starting points:
IPv6 is easy, just try not to be confused by all the digits and letters (DNS will help you, as before). If you know IPv4, there’s not much more to learn in order to understand IPv6 addresses. Go ahead, learn today and we’ll continue in a week!