List of ipv6 support for Tcl.
Unix: http://www.unnumbered.net/~umeno/etc/tclIPv6patch.html also ceptcl provides ipv6 among other protocols.
Windows: http://sf.net/projects/iocpsock
This [L1 ] thread hints at a couple of the challenges in getting Tcl's high-level socket programming interface right.
Stu 2009-06-17 I noticed that Ceptcl wasn't mentioned in that thread, I wonder why. I'd post this to the thread itself but my 'net conn's sporadic lately.