20.4. Router Advertisement Daemon (radvd)

20.4.1.1. Simple configuration

Radvd's config file is normally /etc/radvd.conf. An simple example looks like following:

interface eth0 { 
        AdvSendAdvert on;
        MinRtrAdvInterval 3; 
        MaxRtrAdvInterval 10;
        prefix 3ffe:ffff:0100:f101::/64 { 
                AdvOnLink on; 
                AdvAutonomous on; 
                AdvRouterAddr on; 
        };
};
    

This results on client side in

# ip -6 addr show eth0 
3: eth0: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast qlen 100 
    inet6 3ffe:ffff:100:f101:2e0:12ff:fe34:1234/64 scope global dynamic 
       valid_lft 2591992sec preferred_lft 604792sec 
    inet6 fe80::2e0:12ff:fe34:1234/10 scope link
    

Because no lifetime was defined, a very high value was used.

20.4.1.2. Special 6to4 configuration

Version since 0.6.2pl3 support the automatic (re)-generation of the prefix depending on an IPv4 address of a specified interface. This can be used to distribute advertisements in a LAN after the 6to4 tunneling has changed. Mostly used behind a dynamic dial-on-demand Linux router. Because of the sure shorter lifetime of such prefix (after each dial-up, another prefix is valid), the lifetime configured to minimal values:

interface eth0 { 
        AdvSendAdvert on;
        MinRtrAdvInterval 3; 
        MaxRtrAdvInterval 10;
        prefix 0:0:0:f101::/64 { 
                AdvOnLink off; 
                AdvAutonomous on; 
                AdvRouterAddr on; 
                Base6to4Interface ppp0;
                AdvPreferredLifetime 20; 
                AdvValidLifetime 30;
        };
};
    

This results on client side in (assuming, ppp0 has currently 1.2.3.4 as local IPv4 address):

# /sbin/ip -6 addr show eth0 
3: eth0: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast qlen 100 
   inet6 2002:0102:0304:f101:2e0:12ff:fe34:1234/64 scope global dynamic 
      valid_lft 22sec preferred_lft 12sec
   inet6 fe80::2e0:12ff:fe34:1234/10 scope link
    

Because a small lifetime was defined, such prefix will be thrown away quickly, if no related advertisement was received.

Additional note: if you do not used special 6to4 support in initscripts, you have to setup a special route on the internal interface on the router, otherwise you will get some backrouting problems. for the example showh here:

# /sbin/ip -6 route add 2002:0102:0304:f101::/64 dev eth0 metric 1
    

This route needs to be replaced every time the prefix changes, which is the case after a new IPv4 address was assigned to the dial-up interface.