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IPv6 Address notation

Beware: this is only a comparaison between IPv4 and IPv6. If you don't know IPv4, go get documented about it !

One single IPv6 address

You know IPv4 notation ? It's a.b.c.d (ie. 62.4.20.185) - four numbes between 0 and 255, separated by points
These four numbers encode a 32 bits address
62.4.20.185 -> 3E-04-14-B9 -> 0x3e0414B9 (hex) 111110000001000001010010111001 (bin)

Now lets go to IPv6 notation. It's quite similar. This time it's not points but ':' that separate eight address blocks
and the digits are no longer decimal but hexadecimal (from 0 to f)
These 8 x 4 = 32 digits encode a 128 bits address
3ffe:80e8:00d8:0000:0000:0000:0000:0001 is a valid example

now for us humans, a more practical way to write these very long IP address has been created.

EVERY OPERATING SYSTEM WILL RECOGNISE THIS ABREVIATED NOTATION

1/ the zeros at the beginning of a block don't have to be written

3ffe:80e8:00d8:0000:0000:0000:0000:0001 -> 3ffe:80e8:d8:0:0:0:0:1

2/ when one or several fields are only zeros 3ffe:80e8:d8:0:0:0:0:1
it can be simply shuffled off:

3ffe:80e8:d8:0:0:0:0:1 -> 3ffe:80e8:d8::1

this also works at the end of an IP address

3ffe:80e8:d8:0:0:0:0:0 -> 3ffe:80e8:d8::

to avoid any ambiguous situation a '::' notation can appear only once in an address
the loopback interface (127.0.0.1 in v4) is 0:0:0:0:0:0:0:1, and therefore ::1

A network address

same as in IPv4 actually

the:ipv6:address::/prefixlen

eg. in v4

route: 195.74.192.0/19
descr: EuroNet Belgium

eg. in v6

inet6num: 3FFE:8100::/28
netname: EURONET-BE
descr: 6Bone pTLA

if that doesn't seem clear or you want to change something, don't hesitate, mail

Patrick Viet (pviet@delta6.net)