Auto-configure IPv6 for your Network

One major feature of IPv6 is its ability to auto-configure the host portion of the IP address using the MAC address from the Network Card. We may have seen this already with the local-link address, however, in this tutorial will look at configuring the RAdvD on openSUSE 11 to advertise the Network Prefix and default gateway so we can work with global addresses without any configuration on the hosts. This will differ from DHCP as we do not need to configure the RAdvD with the host addresses. These will come from the hosts own MAC address helping us reach Zero configuration networking. Or at least very little configuration.

Enable IPv6 Routing on the RAdvD Server

Of course, it goes without saying that, we must have IPv6 routing enabled if the server is to route IPv6 packets. Edit the /etc/sysctl.conf line to include the option for this. In openSUSE 11.4 the option is there, just commented out. net.ipv6.conf.all.forwarding = 1

To read these settings into you current configuration, the /proc/sys/net/ipv6/conf/all/forwarding file, use the command sysctl –p . The sysctl.conf file is read at system-boot, so adding the settings to the file makes this change permanent.

Install and Configure RAdvD

Now that IPv6 forwarding is enabled we can install and configure the Route Advertisement Daemon. With openSUSE we can use zypper, other distributions will use yum or apt-get: zypper in radvd. The configuration of radvd is the same across all distributions.

The main configuration is maintained in the file: /etc/radvd.conf. It is always a good idea to make a backup of the original: cp /etc/radvd.conf /etc/radvd.conf.$(date +%F) is a good start. Now we can edit the .conf file. We need to advertise routes only on eth1. So we edit the file as such:

interface eth1

{

};

Any option added in between the braces will be read as configuration for eth1

interface eth1

{

AdvSendAdvert on;
MinRTAdvInterval 3;
MaxRTAdvInterval 10;
AdvDefaultPreference low;
AdvHomeAgent off;

};

These setting represent the minimum to advertise the default route address only to clients. The default route will always be the local-link address of the gateway. This accessible to all clients on the network so becomes the most obvious choice. Clients will send all of their IPv6 Addresses in the header, only those headers originating from non-link-local addresses can be routed. To advertise the network prefix we add another code block inside the eth1 definition, the prefix block.

interface eth1

{

AdvSendAdvert on;
MinRTAdvInterval 3;
MaxRTAdvInterval 10;
AdvDefaultPreference low;
AdvHomeAgent off;
prefix fd81:2041:94e6:1::/64
{
AdvOnLink on;
AdvAutonomous on;
AdvRouterAddr off;
};

};

Here we are advertising a /48 bit ULA (Unique Local Address) subnetted to /64 bits: eth1 represent the subnet 1 and eth0 on the router is connected to subnet 2. Using 64 bits for the network allows 64 bits for the host and then auto-configuration with the hosts MAC address. You can obtain your own ULA from http://www.sixxs.net/tools/grh/ula/ .The ULA is similar to the 192.168. networks we use in IPv4 but, with IPv6, we are encouraged to obtain our own addresses so avoid any overlap as so many billions* of ULAs are available. * (2^41 or 2.2 trillion ULAs: a ULA is identified by the first 7 bits, the total length of aULA is 48 bits giving us 48-7 bits that we can use to create a ULA)

Using the Route Advertisement Daemon only the prefix is needed to be advertised, there is no need to set hosts addresses. Any IPv6 client now can be connected with their own unique address to the fd81:2041:94e6:1::/64 network.

Test from Hosts on your Network

I can start the service with the command rcradvd start. On other distribution service radvd start will work. My network configuration is shown below.

Now it is just time to check our clients. To show that this is truly a protocol feature I will use Windows 7 as my client on the 1 subnet and access the SUSE 10 host with a static IPv6 address across the router on subnet 2. I have made no changes to the Windows 7 box. First see the output of ipconfig from windows 7. You will see the default route and IPv6 address is set. The default gateway is the Link-Local address of my openSUSE box auto-configured by RAdvD.

Now the final graphic shows that using ping -6 fd81:2041:94e6:2::2 we are able to communicate to the different IPv6 network through the router without a pre-configured address or gateway.