The biggest problem in IPv4 is the lack of a big enough
address field, 32 bits, and its capability was not used very
efficiently.
| Address class |
Bits |
Number of nets |
Bits |
Addresses |
| A |
7 |
128 |
24 |
16 777 216 |
| B |
14 |
16 384 |
16 |
65 536 |
| C |
22 |
4 194 304 |
8 |
256 |
One B class net can be replaced by three C class nets if class B is
going to be "empty", but when one address is replaced by
three, the router's memory.
IPv6 in the contrary can support at least
10^12 nodes and 10^9 networks.
The routing algorithm have no knowledge how the
network has been made and can support all IPv4's routing algorithms,
and also support much larger number of hops then IPv4 (limit of 256).
IPv6 can handle different speed of networks, from
Extra Low Frequency networks to very high speed of 500Gbits/s.
IPv6 provide a security layer that places
"options" in separate extension headers while IPv4 does
not. The extension headers can be of arbitrary length and has no
limit to the amount of options that can be carried.
IPv6 has an anycast address that allows nodes to
control the path which their traffic flows, IPv4 does not.
IPv6 headers are extensible, the option in IPv4 is
not efficient to decode.
IPv6 connects to global internet using a combination
of it's global prefixes (see details in IPv6 Addressing) , while IPv4
manually renumbers to connect to the internet. IPv6 renumbers
automatically.
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