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IPv6, IPv4 address priority question

Started by tjj70302, January 10, 2010, 06:53:17 AM

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hi, all

i am completely new to the world of ipv6, just successfully set up a tunnel thru HE. please bear with me if the question is noob.

for some reasons, i didn't use the "Anycasted IPv6 Caching Nameserver" and i can still browse http://ipv6.google.com, so i suppose the original DNS server i use, which is opendns.com is capable of resolving the IPv6 address.

here comes the question, i know ipv6.google.com only has a IPv6 address, so i can't browse it before i setup a tunnel. but for some sites which have both IPv4 and IPv6 address, which IP address will be resolved at a higher priority? or if both addresses are resolved and returned to my computer, is there a mechanism to control which ip address my computer to choose?

thanks in advance



It's decided by the OS...what OS are you running?


ipv6.google.com will return IPv6 addresses, where google.com normally will not, unless the name server is "whitelisted" by google, which he's anycasted server is.  So using ipv6.google.com will give you IPv6 regardless, and if you use the anycasted server, you'll get ipv6 where available just going to google.com or <xyz>.google.com

The application and OS make the decision on what address to use.  Unix Linux, there's the "ip addrlabel" and gai.conf file setups which determine how to preference things, along with anything the application may do.  Under windows it's the "netsh int ipv6 int show/set prefixpolicy" I believe, plus anything that application may do.

In general, both linux and windows in applications like web browsers will prefer an IPv6 address unless it's a 6to4 or Teredo address, in which case it will prefer IPv4.

Also, I should say I've tried to change the default preferences under windows while using Teredo for by modifying the "prefixpolicy" but it seemed not to make a difference (I must be doing something wrong or missing something, or it's simply hard coded into the OS or applications I tried).


thanks jimb, it's pretty clearly explained.

i mainly use the Mac OSX, and i tried a little bit yesterday after i posted this question, it seems that Safari would prefer ipv6 address without any configuration.

but still, it will be fun to check and play around with "ip addrlabel" and "gai.conf" you mentioned, it is a good startpoint.


If you install the "ShowIP" addon for Firefox, you get a green IPv6 address or a red IPv4 address in your status bar.


As has been often stated, ShowIP is a dns tool, not a connectivity one. Its not an indicator you're actually connecting to a site via IPv6 :)


Is there any way to get Firefox to admit what IP address it obtained a page from?


"Netstat -a" will show you what connections your OS has made, but I don't know of a way to tie that to a specific program


Quote from: kriteknetworks on January 26, 2010, 07:38:45 AM
As has been often stated, ShowIP is a dns tool, not a connectivity one. Its not an indicator you're actually connecting to a site via IPv6 :)
It does seem to make an effort to figure out which one you're actually connecting to.  At least with me it usually does a good job of it unless you pull the rug out from under it.  :P


This seems silly to me. Firefox knows what it connected to, doesn't it? It should be possible to make it spit that information out.


Quote from: bombcar on January 26, 2010, 05:15:13 PM
This seems silly to me. Firefox knows what it connected to, doesn't it? It should be possible to make it spit that information out.
Yes.  But the question is, do plugins have access to this information?

Another problem would be, when you go to a web page, the page often opens a bunch of connections to load images, ads, whatever.  So the plugin would somehow have to differentiate between these and the URL connection.  This could likely be done by resolving the DNS of the URL and cross referencing it to the connection information (presuming it's available to the plugin).

It could also possibly call a system function to get a "netstat" style list and cross reference it with the FF PID & DNS answers, it would work, but it might be a bit slow.



Hi 2 all

Please help me to setup ipv6 priority in windows 7.

in this page i see Top Websites Running IPv6,
for example , tribune.com 2002:a3c0:1712::a3c0:1712
i can ping it (by ipv6), but if i visit this site by dns name, in my dns cache i see ipv4.

how i can raise the priority to ipv6 using?

sorry for my english  ;)


If you do a "ping -6 sitename" does it resolve?

Is your DNS server IPV6 capable?


i have written that if i do a "ping -6 sitename" it was pinged and resolved normally some times ago, but now it is down.
it was resolved only by ipv4... strange

Now I can normally ping some others sites, for example tokyotosho.info 2001:470:dc56:b00::25:1
C:\Windows\system32>ping tokyotosho.info

Pinging tokyotosho.info [2001:470:dc56:b00::25:1] with 32 bytes of data:
Reply from 2001:470:dc56:b00::25:1: time=77ms
Reply from 2001:470:dc56:b00::25:1: time=89ms
Reply from 2001:470:dc56:b00::25:1: time=78ms
Reply from 2001:470:dc56:b00::25:1: time=79ms

.. and it is resolve normally in ipv4 and ipv6, but how can i recognize, which protocol (ipv4 or ipv6) was used by my browser (ie or firefox), when i go to this sites by url? and where i can adjust priority of ip protocols using?

p.s. i do not know about my dns server, i use tunnel through HE