Usage of IPv6 on OS X

[drunkenfreak]

Hi,

I'm using quite a while IPv6 on Mac OS X (Lion newest updates). My new server also got IPv6 and now I can really start playing around with it and mentioned some really strange things:

- IMAP and SMTP doesn't work with Mail.app if IPv4 is enabled
- HTTP on a IPv6 enabled site is using v6 and v4 on the same request some parts are downloaded with v6 and other parts with v4 (no ads, just the website, monitored with Wireshark).
- most CLI-Tools (ssh, rsync...) doesn't use v6 if the option isn't explicitly applied. On my homenetwork as well as on the internet
- each time a new v6-address from the pool and one static v6-address, but this should just be the privacy flag in the implementation

What ist wrong with the IPv6 stack in OS X? Shouldn't v6 preferred if it is available?

[kcochran]

Lion enables what is often termed "Happy Eyeballs" for anything using the higher level networking functions (CFStreamSocket and higher).  Basically, it'll try v4 and v6 at the same time, and whatever responds first will be tried first the next time.