IPv6 Address : Panjang Prefix untuk Routing
Sumber: http://tldp.org/HOWTO/Linux+IPv6-HOWTO/x684.html
Pada awal proses disain, sebetulnya direncanakan untuk menggunakan pendekatan routing yang betul-betul berjenjang untuk bisa mengurangi tabel routing semaksimal mungkin. Alasannya, karena jumlah entri routing IPv4 di core router > 104 ribu (Mei 2001), dengan cara tersebut mengurangi kebutuhan memory di router untuk menyimpan tabel routing dan menaikan kecepatan (dengan sedikit entri maka lebih mempercepat proses pencarian).
Todays view is that routing will be mostly hierarchically designed for networks with only one service provider. With more than one ISP connections, this is not possible, and subject to an issue named multi-homing (infos on multi-homing: drafts-ietf-multi6-*,IPv6 Multihoming Solutions).
Panjang Prefix (juga dikenal sebagai netmask)
Similar to IPv4, the routable network path for routing to take place. Because standard netmask notation for 128 bits doesn't look nice, designers employed the IPv4 Classless Inter Domain Routing (CIDR, RFC 1519 / Classless Inter-Domain Routing) scheme, which specifies the number of bits of the IP address to be used for routing. It is also called the "slash" notation.
An example:
2001:0db8:100:1:2:3:4:5/48
This notation will be expanded:
Network:
2001:0db8:0100:0000:0000:0000:0000:0000
Netmask:
ffff:ffff:ffff:0000:0000:0000:0000:0000
3.4.2. Matching a route
Under normal circumstances (no QoS), a lookup in a routing table results in the route with the most significant number of address bits being selected. In other words, the route with the biggest prefix length matches first.
For example if a routing table shows following entries (list is not complete):
2001:0db8:100::/48 :: U 1 0 0 sit1 2000::/3 ::192.88.99.1 UG 1 0 0 tun6to4
Shown destination addresses of IPv6 packets will be routed through shown device
2001:0db8:100:1:2:3:4:5/48 -> routed through device sit1 2001:0db8:200:1:2:3:4:5/48 -> routed through device tun6to4