[Dnsmasq-discuss] ssl.google-analytics.com doesnt like to be cached?

[Simon Kelley]

koko wrote:
> rasz at capek:/etc$ sudo tcpdump -i eth0 udp dst port 53 or udp src port 53
> 
> open this:
> http://www.adhocelectronics.com/Products/XTend-PKG-Radio-Modems-900MHz-1W
> 
> 
> 19:32:09.749449 IP 82-mi3-3.acn.waw.pl.2334 >
> patyczak1.aster.pl.domain:  53777+ AAAA? www.adhocelectronics.com.
> (42)
> 19:32:10.820178 IP patyczak1.aster.pl.domain >
> 82-mi3-3.acn.waw.pl.2334:  53777 1/0/0 CNAME[|domain]
> 19:32:10.914475 IP 82-mi3-3.acn.waw.pl.2334 >
> patyczak1.aster.pl.domain:  1154+ A? www.adhocelectronics.com. (42)
> 19:32:11.129926 IP patyczak1.aster.pl.domain >
> 82-mi3-3.acn.waw.pl.2334:  1154 2/0/0 CNAME[|domain]
> 19:32:24.797908 IP 82-mi3-3.acn.waw.pl.2334 >
> patyczak1.aster.pl.domain:  21805+ AAAA? ssl.google-analytics.com.
> (42)
> 19:32:24.896106 IP patyczak1.aster.pl.domain >
> 82-mi3-3.acn.waw.pl.2334:  21805 1/0/0 CNAME[|domain]
> 19:32:40.240099 IP 82-mi3-3.acn.waw.pl.2334 >
> patyczak1.aster.pl.domain:  45922+ AAAA? ssl.google-analytics.com.
> (42)
> 19:32:40.429649 IP patyczak1.aster.pl.domain >
> 82-mi3-3.acn.waw.pl.2334:  45922 1/0/0 CNAME[|domain]
> 
> 
> reload page, and again
> 
> 
> 19:37:18.645708 IP 82-mi3-3.acn.waw.pl.2334 >
> patyczak1.aster.pl.domain:  52312+ AAAA? ssl.google-analytics.com.
> (42)
> 19:37:18.706598 IP 82-mi3-3.acn.waw.pl.2334 >
> patyczak1.aster.pl.domain:  37353+ PTR? 211.39.76.212.in-addr.arpa.
> (44)
> 19:37:18.714008 IP patyczak1.aster.pl.domain >
> 82-mi3-3.acn.waw.pl.2334:  37353 1/0/0 (76)
> 19:37:18.770070 IP 82-mi3-3.acn.waw.pl.2334 >
> patyczak1.aster.pl.domain:  44107+ PTR? 82.134.210.82.in-addr.arpa.
> (44)
> 19:37:18.843731 IP patyczak1.aster.pl.domain >
> 82-mi3-3.acn.waw.pl.2334:  44107 1/0/0 (77)
> 19:37:19.418428 IP patyczak1.aster.pl.domain >
> 82-mi3-3.acn.waw.pl.2334:  52312 1/0/0 CNAME[|domain]
> 
> 
> rasz at capek:/etc$ grep <hosts ssl.google-analytics.com
> 127.0.0.1       ssl.google-analytics.com
> 
> go to http://ssl.google-analytics.com/ and its nicely cached ..., go
> to 
> http://www.adhocelectronics.com/Products/XTend-PKG-Radio-Modems-900MHz-1W
> again and it will ask the dns again. What is going on? What am I
> missing?
> 

Looking more closely at the data dump, almost all of the repeated 
queries are for AAAA records, ie IPv6. I guess that your web-browser has 
IPv6 enabled, and is trying IPv6 first. In an ideal world, dnsmasq would 
cache the negative replies to AAAA queries, it would know that 
ssl.google.analytics doesn't have an IPv6 address, and not send the 
query upstream each time. It can't always do this: if the upstream 
server doesn't include SOA records then dnsmasq doesn't have enough 
information for negative caching.

The best solution might be to disable IPv6 either in the browser or in 
the kernel.


Cheers,

Simon.