(usagi-users 02111) Re: multiproto bind() ?

["Eva M. Castro" <ecastro@xxxxxxxxxx>]

Abdul Basit wrote:

> i want to distinguish between clients coming to ipv4 or ipv6
> and print client address ? if i would get sa_family correct
> i can switch(family) { and case for AF_INET and AF_INET6 and
> use inet_ntop to print address ? but i am getting same family
> always (28c/bsd and 10c/linux --> AF_INET6)
>
> any hints?

When an IPv4 client connects to your server, the connection is established
using an IPv4-mapped IPv6 address, for instance, if your IPv4 client
is running at host using a.b.c.d IPv4 address, the IPv4-mapped IPv6
address will be:
::FFFF:a.b.c.d

Then, your IPv6 server will always use IPv6 addresses,
IPv6 addresses when connections come from IPv6 hosts and
IPv4-mapped IPv6 addresses when connections come from IPv4 hosts.
This is the reason you always print AF_INET6.

You can see how it works:
http://jungla.dit.upm.es/~ecastro/IPv6-web/ipv6.html
in the figure "IPv6 server on dual stack".

There is a macro definition to check if an address is IPv4-mapped IPv6
address:

IN6_IS_ADDR_V4MAPPED

Using this macro you can check if the client connections come from
IPv4 or IPv6 host.

I hope it helps,

eva