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www.sixxs.net not accessible via firefox+6to4
[us] Stuart D Gathman on Friday, 22 July 2011 17:35:57
At home, I have 6to4 configured for IP6. Firefox browses ipv6.google.com with no problem, and tcpdump confirms exchange takes place via IPv6. However, www.sixxs.net is loaded as IPv4. The ShowIP firefox addon shows the IPv6 IP, but sixxs.net shows IPv4 at the bottom, and tcpdump confirms that the exchange takes place via IPv4. At the office, we have a sixxs.net tunnel in addition to 6to4. When I set my IPv6 gateway to the 6to4 gateway, I get the same problem. When I set it to the sixxs gateway server, firefox loads sixxs.net via IPv6. To compound the mystery, wget -6 loads www.sixxs.net just fine. elinks loads www.sixxs.net via IPv4 - but loads ipv6.google.com via IPv6. Theories that the facts have shot down: 1) sixxs.net rejects 6to4 connections (works with wget) 2) firefox disables IPv6 when only 6to4 is available (works with ipv6.google.com) At this point, my theory is that when the local IP6 is 6to4, then firefox prefers IPv4 addresses (but uses IP6 when no IPv4 is available).
www.sixxs.net not accessible via firefox+6to4
[ch] Jeroen Massar SixXS Staff on Friday, 22 July 2011 17:43:03
The ShowIP firefox addon shows the IPv6 IP
Because ShowIP simply does a DNS lookup and nothing else. It is pretty useless tool anyway as a lot of sites get a lot of their resources from other hosts.
1) sixxs.net rejects 6to4 connections (works with wget)
Nonsense, why would we bother filtering that out there? And anyway, as you stated tcpdump does not show that you are making IPv6 connections at all.
2) firefox disables IPv6 when only 6to4 is available (works with ipv6.google.com)
Please read RFC3484 which states things about address selection. It depends quite a bit on the operating system (which you forgot to mention the one you have) what happens, but according to RFC3484 6to4 is a last resort and if a destination has both IPv6 + IPv4, but the source is 6to4 then IPv4 should be used, because, why tunnel if you are using IPv4 anyway? Try http://www.ipv6.sixxs.net as that should work as it only has an AAAA record. You also might want to read up on why various people in the IETF are discussing getting 6to4 set to historic and even going as far as disabling it altogether. Generally it has more problems than the benefits you will get from it.
www.sixxs.net not accessible via firefox+6to4
[us] Stuart D Gathman on Friday, 22 July 2011 18:01:39
Thank you for confirming my theory with the RFC reference. So I was right, firefox *is* preferring IPv4 when the gateway is 6to4 - and this is according to RFC.
www.sixxs.net not accessible via firefox+6to4
[ch] Jeroen Massar SixXS Staff on Friday, 22 July 2011 19:40:52
Depending on the OS and then the tool (as it then depends on if it uses getaddrinfo(AF_UNSPEC) or does separate requests for IPv6 + IPv4 which some tools does). No idea what firefox does, especially as it changes per version.
www.sixxs.net not accessible via firefox+6to4
[cz] Ruslan Marchenko on Friday, 22 July 2011 20:34:00
My FF5.0@Win7x64 prefers AAAA to A.
www.sixxs.net not accessible via firefox+6to4
[cz] Ruslan Marchenko on Saturday, 23 July 2011 22:18:08
FF5@UbuntuNattyx64 as well
www.sixxs.net not accessible via firefox+6to4
[us] Stuart D Gathman on Saturday, 23 July 2011 22:24:01
I have firefox-3.6.18 ... should have mentioned that.
www.sixxs.net not accessible via firefox+6to4
[de] Matthias Versen on Tuesday, 26 July 2011 23:56:16
Gecko is using whatever getaddrinfo hands back and it doesn't make a conscious decision to "favor" one or the other. It seems that in the case of 6to4 the OS hands back an A record as first result while the OS hands back an AAAA record as first result with a "real" ipv6 connection. This is known to be done on purpose by miredo as example. Another feature is in the nightly builds: Gecko switches back to IPv4 if the IPv6 connection is 300ms slower than the IPv4 connection. * Gecko is the rendering engine that does all the html parsing, layout, networking, images...
www.sixxs.net not accessible via firefox+6to4
[ch] Jeroen Massar SixXS Staff on Wednesday, 27 July 2011 09:49:22
It seems that in the case of 6to4 the OS hands back an A record as first result while the OS hands
back an AAAA record as first result with a "real" ipv6 connection. This is known to be done on
purpose by miredo as example.
That is what RFC3484 defines ;)

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