[Server-devel] [Sugar-devel] Notes on service discovery XS/XO

[Iñaki Arenaza]

Martin Langhoff <martin.langhoff at gmail.com> writes:

>> also note that this will require that you run some sort of DNS cache on the
>
> The standard dns resolver libs on linux (part of glibc?) caches
> alright. All platforms I know cache things alright, and it's fairly
> serious bug if your OS doesn't.

I'm afraid that's not always true. Running Debian Lenny here without
nscd, configured to query an external DNS server (I normally run bind
locally, but I changed resolv.conf for the tests and stopped bind).

I've used tcpdump to dump DNS traffic while running 'ping -n
some.valid.dns.name -c 3'. Everytime I re-launch the ping command, a new
query is sent out. If I remove the '-n' in the ping command, a reverse
query is sent for each iteration of the ping (to print the remote end
name).

Even installing and enabling nscd doesn't seem to change that (nscd
doesn't cache hosts queries on Debian, see Debian bug #335476).

I've tried other things like telneting to an external host and firefox
browsing the same page repeatedly (closing firefox between request so
firefox internal caches don't play tricks on me), and it seems
consistent.

So at least in Debian, glibc doesn't seem to cache DNS queries by
default.
 
Iñaki.

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