Firefox Loses DNS in F10 (also: UDP checksum errors for DNS queries)

[Andre Costa]

Hi,

On Mon, Dec 1, 2008 at 20:51, Andre Costa <blueser at gmail.com> wrote:

> Hi,
>
> On Mon, Dec 1, 2008 at 13:19, Tom Horsley <tom.horsley at att.net> wrote:
>
>> On Mon, 01 Dec 2008 09:45:22 -0500
>> Richard Heck <rgheck at comcast.net> wrote:
>>
>> >
>> > I've been seeing a weird problem on F10 in Firefox on a fresh install
>> > onto my daughter's machine. Frequently, after using Firefox for a bit,
>> > it seems to lose its ability to do DNS lookups. Every URL reports not
>> > found. Shutting it down and reopening solves the problem. So it's just
>> > Firefox, not the whole system. Any ideas?
>>
>> I see a comcast.net in your address, which probably means this is the
>> problem:
>>
>> https://bugzilla.redhat.com/show_bug.cgi?id=459756
>>
>> It is random, but because you use firefox more, you see it more there.
>>
>> I got rid of the problem by running named as a local dns cache and
>> starting it with the -4 option so it only does IPv4 requests.
>>
>
> That's weird, I've been seing this a lot too. I use dnsmasq as my local DNS
> cache, but Firefox keeps asking over and over again for the same addresses
> (I mean it keeps displaying "Locating xxx" when xxx has just been accessed,
> which means it's on dnsmasq's cache).
>
> I already have "network.dns.disableIPv6" set to true on FF's configuration,
> and I added "install ipv6 /bin/true" to /etc/modprobe.conf to disable ipv6.
>
> So, could this be indeed a Firefox bug? (doesn't seem so, but...)
>
> Regards,
>
> Andre
>

I got some additional info: it seems all cached replies to DNS queries are
being sent with wrong UDP checksum. Also, outbound queries are also going
with wrong checksum.

I ran wireshark to analyze DNS traffic and 100% of the replies from
127.0.0.1 (dnsmasq) report incorrect checksum, and wireshark even suggests
"maybe caused by UDP checksum offload?". All outbound queries (when dnsmaq
doesn't have an address and relays the query to the external servers) also
show the same problem.

It doesn't seem to be a dnsmasq problem, because queries sent by 'dig' for
example also have wrong checksum. Could this be a problem at a lower level
(such as the kernel driver for my ethernet controller)? Actually, is this a
problem at all or can I safely ignore this?

(my ethernet controller is an onboard Intel 82566 DC-2 Gigabit)

Can someone else also run wireshark to see if they're getting checksum
errors as well?

Regards,

Andre
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