2.4 Configuring IPv6 addresses

Every PC in the testbed (except the Mobile Host) has a pair of interfaces: one interface is connected to the upper part of the tree and the other to the lower PCs:

• Upper interface (to the root of the tree): It automatically configures an IPv6 address from a radvd (Router Advertisement daemon).
• Lower interface: It has a fixed IPv6 address and has a radvd to announce the prefix subnetwork to the Mobile Hosts that come to this subnetwork (if they are Base Stations).

The radvd (Router Advertisement daemon) sends periodically packets informing about its subnetwork prefix. A Mobile Host that receives these messages can automatically configure its IPv6 address and attach to this subnetwork. An example message sent by a radvd is:

	Router advertisement from fe80::250:4ff:fe47:d29a (hoplimit 255)
        AdvCurHopLimit: 64
        AdvManagedFlag: off
        AdvOtherConfigFlag: off
        AdvHomeAgentFlag: off
        AdvReachableTime: 0
        AdvRetransTimer: 0
        Prefix fec0:0:0:1::/64
                AdvValidLifetime: 2592000
                AdvPreferredLifetime: 604800
                AdvOnLink: on
                AdvAutonomous: on
                AdvRouterAddr: off
        AdvSourceLLAddress: 00 50 04 47 D2 9A

This message means that it has been sent by a host with fe80::250:4ff:fe47:d29a IPv6 address and it advertises that the subnetwork prefix is fec0:0:0:1::/64.

The configuration file (in /etc/radvd.conf) for this message is the next:

	interface eth0
        {
                AdvSendAdvert on;
                MaxRtrAdvInterval 10;
                #AdvSourceLLAddress off;
                prefix fec0:0:0:1::/64
                {
                        AdvOnLink on;
                        AdvAutonomous on;
                };
        };

When a Mobile Host receives a Router Advertisement, it automatically configures an adequated IPv6 address for this subnetwork. It takes the subnetwork prefix and adds its MAC address. For example, a host with MAC address 00:50:DA:4F:A7:87 and the previous Router Advertisement obtains the IPv6 address fec0::1:250:daff:fe4f:a787.

To configured the fixed IPv6 address you have to specify them in the /etc/network/interfaces file. You sould add lines like these (for example, for the subnetwork 4):

	iface eth2 inet6 static
        address fec0::5:202:a5ff:fe6e:5209
        netmask 64