Datasheet

“main” (Installation and Administration) — 2004/6/25 — 13:29 — page 425 — #451
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21
Linux in the Network
21.2.2 The IPv6 Address System
As mentioned, the current IP protocol is lacking in two important aspects:
there is an increasing shortage of IP addresses and configuring the net-
work and maintaining the routing tables is becoming a more complex and
burdensome task. IPv6 solves the first problem by expanding the address
space to 128 bits. The second one is countered by introducing a hierarchi-
cal address structure, combined with sophisticated techniques to allocate
network addresses, as well as multihoming (the ability to allocate several
addresses to one device, giving access to several networks).
When dealing with IPv6, it is useful to know about three different types of
addresses:
Unicast Addresses of this type are associated with exactly one network
interface. Packets with such an address are delivered to only one des-
tination. Accordingly, unicast addresses are used to transfer packets
to individual hosts on the local network or the Internet.
Multicast Addresses of this type relate to a group of network interfaces.
Packets with such an address are delivered to all destinations that
belong to the group. Multicast addresses are mainly used by certain
network services to communicate with certain groups of hosts in a
well-directed manner.
Anycast Addresses of this type are related to a group of interfaces. Pack-
ets with such an address are delivered to the member of the group
that is closest to the sender, according to the principles of the underly-
ing routing protocol. Anycast addresses are used to make it easier for
hosts to find out about servers offering certain services in the given
network area. All servers of the same type have the same anycast ad-
dress. Whenever a host requests a service, it receives a reply from the
server with the closest location, as determined by the routing proto-
col. If this server should fail for some reason, the protocol automati-
cally selects the second closest server, then the third one, and so forth.
Structure of an IPv6 Address
An IPv6 address is made up of eight four-digit fields, each of them repre-
senting sixteen bits, written in hexadecimal notation. They are also sep-
arated by colons (:). Any leading zero bytes within a given field may be
dropped, but zeros within the field or at its end may not. Another conven-
tion is that more than four consecutive zero bytes may be collapsed into a
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SUSE LINUX Enterprise Server