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Hi,<br>
<br>
I have noticed lately on several machines using the local cable ISP
in my neck of the woods, that using the DHCP supplied DNS servers
from my ISP is significantly slower than using a global DNS service
like OpenDNS. With that in mind I configured the Linux box I use at
home to use OpenDNS. It was working great, until I decided to fix it
by adding DNSMASQ as a local caching server to lighten the load. It
works fine most of the time, but sometimes I get intermittent
failures to resolve names. At first I just noticed delays getting to
some websites, and occasionally it would fail entirely. At times
though it became unacceptable and failed a lot. So, I started
testing name resolution in a shell using the "host" command, and
found that it did indeed sometimes give me a ";; connection timed
out; no servers could be reached" error. When I specifically ask the
host command to query the OpenDNS server directly, bypassing
DNSMASQ, it never fails and is always very fast.<br>
<br>
I got really curious about this and captured some packets with
Wireshark. First of a host query going through DNSMASQ that failed,
and then one going directly to the DNS server. I did indeed get no
reply back on the query that failed. The only difference I could
find between the packets being sent to OpenDNS by DNSMASQ, and those
going direclty from the OS to OpenDNS, is that the queries that
failed from DNSMASQ had the DF (don't fragment) bit set. Now it is
quite possible I'm missing something here, but it occurs to me that
my using DNS servers half way across the internet, rather than right
down the street at the local ISP, could be causing packets with the
DF bit set to get dropped. Is there any way to tell DNSMASQ to not
set the DF bit? Can anyone think of another reason why this is
failing for me?<br>
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<i><b>Regards,<br>
Stuart<br>
<br>
<br>
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