939553 - DNS errors lead Firefox to believe that only IPv6 websites are available.

Status: RESOLVED DUPLICATE of bug 939318

(Core :: Networking: DNS, defect)

Description

[Xuân Baldauf]

User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:25.0) Gecko/20100101 Firefox/25.0 (Beta/Release)
Build ID: 2013102400

Steps to reproduce:

1. My client computer has only IPv4 connectivity (the OS is IPv6 enabled, but the router only delivers IPv4 addresses).
2. I attempted to access a website which has both IPv4 and IPv6 DNS records (both A and AAAA) (e.g. http://www.google.com/)
3. Due to network communication errors, the A DNS reply did not reach the client computer (and thus the browser).
4. The AAAA DNS reply actually did reach the client computer (and thus the browser).
5. Because the client computer has no IPv6 connectivity, the connection attempt to connect to the IPv6 address failed immediately.
6. Because all connection methods (TCP over IPv4 as well as TCP over IPv6) were exhausted, Firefox displayed that the website (http://www.google.com/) was not reachable.
7. I tried again by attempting to reload the website (Ctrl+R)


Actual results:

The website (http://www.google.com/) was reported as not reachable.
This, however, is not true.


Expected results:

At least once Firefox detected that the website was not reachable by IPv6, Firefox should have noticed that not having an A DNS record for the IPv4 address of the website was due to a temporary error, and try again resolving the A DNS record. If Firefox had tried again, then it would have succeeded in receiving a A DNS record and thus would have succeeded in connecting to the website.

Comment 1

[Dave Fennell]

I got really stuck with what I believe is the same issue. I have ipv6 disabled on my desktop machine via a kernel parameter because it was causing problems with something in the past:

GRUB_CMDLINE_LINUX="ipv6.disable=1"

Firefox was refusing to access certain aliased domains, even thought the dns could resolve them correctly (to an ipv4 address). Once I enabled ipv6 they started working even though as far as I can tell they are not even ipv6 addresses.  It looks like Firefox does not check for system ipv6 support but depends upon it.  I have had this setup for some time but never really had any problems until Firefox 26.

Comment 2

[Xuân Baldauf]

I had this problem again. It happens when I roam into a WiFi network which actually has IPv6 enabled (and thus has an IPv6 default route) and _then_ roam into another WiFi network which actually has IPv6 not enabled (and thus does not have an IPv6 default route).

I would suspect this code line http://mxr.mozilla.org/mozilla-release/source/netwerk/protocol/http/nsHttpConnectionMgr.cpp#2738

tmpFlags |= nsISocketTransport::DISABLE_IPV4;

as the culprit of this bug.