IPv6 Server: Router Advertisement Daemon (radvd)

Daemon router advertisement sangat bermanfaat di LAN, terutama jika client yang ada bisa di konfigurasi secara automatis. Daemon itu sendiri harus di jalankan di router Linux yang merupakan default gateway IPv6. Perlu di catat bahwa belum tentu gateway IPv6 adalah gateway IPv4 juga.

Kita dapat menentukan beberapa informasi dan flag yang harus di bawa di advertisement. Yang banyak digunakan adalah:

• Prefix (needed)
• Lifetime dari prefix
• Banyaknya pengiriman advertisement (optional)

Sesudah di konfigurasi dengan benar, daemon akan mengirimkan advertisement melalui interface yang di tentukan dan client "semoga" menerima-nya dan mengkonfigurasi adddress secara automatis dengan prefix yang di terima dan route default.

Konfigurasi radvd

Konfigurasi Sederhana

File konfigurasi Radvd biasa /etc/radvd.conf. Contoh sederhana sekali adalah sebagai berikut:

interface eth0 { 
        AdvSendAdvert on;
        MinRtrAdvInterval 3; 
        MaxRtrAdvInterval 10;
        prefix 2001:0db8:0100:f101::/64 { 
                AdvOnLink on; 
                AdvAutonomous on; 
                AdvRouterAddr on; 
        };
};

Hasil yang akan di peroleh di sisi client adalah:

# ip -6 addr show eth0 

3: eth0: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast qlen 100 
    inet6 2001:0db8:100:f101:2e0:12ff:fe34:1234/64 scope global dynamic 
       valid_lft 2591992sec preferred_lft 604792sec 
    inet6 fe80::2e0:12ff:fe34:1234/10 scope link

Jika tidak ada lifetime yang di definisikan, maka nilai yang sangat tinggi yang akan di gunakan.

Konfigurasi khusus 6to4

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.

22.4.2. Debugging

A program called “radvdump” can help you looking into sent or received advertisements. Simple to use:

# radvdump 
Router advertisement from fe80::280:c8ff:feb9:cef9 (hoplimit 255) 
        AdvCurHopLimit: 64 
        AdvManagedFlag: off 
        AdvOtherConfigFlag: off 
        AdvHomeAgentFlag: off 
        AdvReachableTime: 0 
        AdvRetransTimer: 0 
        Prefix 2002:0102:0304:f101::/64 
                AdvValidLifetime: 30 
                AdvPreferredLifetime: 20 
                AdvOnLink: off 
                AdvAutonomous: on 
                AdvRouterAddr: on 
        Prefix 2001:0db8:100:f101::/64 
                AdvValidLifetime: 2592000 
                AdvPreferredLifetime: 604800 
                AdvOnLink: on 
                AdvAutonomous: on 
                AdvRouterAddr: on 
        AdvSourceLLAddress: 00 80 12 34 56 78

Output shows you each advertisement package in readable format. You should see your configured values here again, if not, perhaps it's not your radvd which sends the advertisement...look for another router on the link (and take the LLAddress, which is the MAC address for tracing).