IPv6 AUtoConfiguration: Stateful auto-configuration menggunakan Router Advertisement Daemon (radvd)

router advertisement daemon sangat bermanfaat di LAN, terutama jika client harus auto-configure. Daemon itu sendiri harus jalan di linux dengan default IPv6 gateway router. Perlu di catat bahwa tidak ada keharusan RAdvD ini merupakan gateway default IPv4 juga, oleh karena itu perhatikan baik-baik siapa yang mengirimkan router advertisement di LAN.

Kita dapat memberikan beberapa informasi dan flag yang dikirim dalam advertisement. Yang umum dikirim adalah

• Prefix (ini di perlukan)
• Waktu hidup dari prefix
• Banyaknya pengiriman advertisement (bukan keharusan)

Setelah konfigurasi yang benar, maka daemon akan mengirimkan advertisement melalui interface yang di tentukan dan client semoga akan menerima advertisement tersebut dan kan secara automatis mengkonfigurasi alamat dengan prefix dan route default yang di advertise.

Mengkonfigurasi radvd

Konfigurasi Sederhana

File konfigurasi radvd biasanya /etc/radvd.conf. Contoh sederhana adalah sebagai berikut:

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

Hasil disisi cliet 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

Karena tidak ada lifetime yang diset, nilai yang sangat tinggi akan digunakan.

Konfigurasi khusus untuk 6to4

Sejak versi 0.6.2pl3 mendukung automatic (re)-generation dari prefix tergantung pada address IPv4 di interface. Ini dapat digunakan untuk mendistribusikan advertisement di LAN sesudah tunnel 6to4 berubah. Ini biasanya digunakan di belakang dynamic dial-on-demand Linux router. Karena lifetime prefix seperti itu sangat pendek (setiap dial-up, prefix lain yang valid), maka lifetime biasanya di konfigurasi dengan nilai yang sangat minimal.

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).