Datasheet

“main” (Installation and Administration) — 2004/6/25 — 13:29 — page 423 — #449

Linux in the Network

Under the current IPv4 protocol, DHCP or NAT (network address transla-

tion) are the typical mechanisms used to circumvent the potential address

shortage. Combined with the convention to keep private and public ad-

dress spaces separate, these methods can certainly mitigate the shortage.

The problem with them lies in their conﬁguration, which is a chore to set

up and a burden to maintain. To set up a host in an IPv4 network, you need

a number of address items, such as the host’s own IP address, the subnet-

mask, the gateway address, and maybe a name server address. All these

items need to be known and cannot be derived from somewhere else.

With IPv6, both the address shortage and the complicated conﬁguration

should be a thing of the past. The following sections tell more about the

improvements and beneﬁts brought by IPv6 and about the transition from

the old protocol to the new one.

21.2.1 Advantages of IPv6

The most important and most visible improvement brought by the new

protocol is the enormous expansion of the available address space. An IPv6

address is made up of 128 bit values instead of the traditional 32 bits. This

provides for as many as several quadrillion IP addresses.

However, IPv6 addresses are not only different from their predecessors

with regard to their length. They also have a different internal structure

that may contain more speciﬁc information about the systems and the

networks to which they belong. More details about this are found in Sec-

tion 21.2.2 on page 425.

The following is a list of some other advantages of the new protocol:

Autoconﬁguration IPv6 makes the network “plug and play” capable,

which means that a newly set up system integrates into the (local)

network without any manual conﬁguration. The new host uses its

autoconﬁg mechanism to derive its own address from the informa-

tion made available by the neighboring routers, relying on a proto-

col called the neighbor discovery (ND) protocol. This method does not

require any intervention on the administrator’s part and there is no

need to maintain a central server for address allocation — an addi-

tional advantage over IPv4, where automatic address allocation re-

quires a DHCP server.

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