TCP/IP library?

Is there any free software C++ library that:

1) Can listen on a socket creating a thread for each
socket accepted, so that the socket is automagickly closed when
the thread exits.
2) handle IPv6 vs IPv4 issues transparently.
3) Have a well designed API.
4) be as portable as possible, but definitely run on Linux?

Thank You.

--
Paul Elliott 1(512)837-1096
(E-Mail Removed) PMB 181, 11900 Metric Blvd Suite J
http://www.io.com/~pelliott/pme/ Austin TX 78758-3117