[Freeswitch-users] info about sofia sip dns cache and graylisting?

[Michel Brabants]

Hello all,

we have a problem with a 1.4-version of Freeswitch that FS goes to 100%
cpu. The problem has been traced to a dns-cache-problem. The dns-cache
contains srv-records, which should have 2 a-records, but they have 100's of
a-records, which are mostly the same (some with a different priority). This
causes FS do to a lot of compares (to sort the records) and it goes to 100%
cpu in the end.
The priority almost never is the original priority, so I was thinking that
the cache is maybe growing because of graylisting of entries, causing the
priority to increase and the ttl to be reset.

The code is however very difficult to follow as it is all event-based and
part of big C-structs in sofia-sip. A bug in the gdb-debugger causing
static variables to be almost unreadable makes life not much easier. The
graylisting policy, as well as the dns cache policy is not really
documented as far as I can find, so any info about this would be great.

Anyway, my current thought is that the dns-cache is maybe growing, becuase
the graylisting-code sets the priority to a higher value and resets the ttl
to a certain value (no idea which one, but the default is 10 minutes and
the maximum a day). The srv-record-compare-function however checks also
using priority and weight and returns a negative response if they are
different. I would think that fs maybe then readds the original srv-records
(with priority 0) when it requeries the dns. Those entries will also
increase in priority and ttl when they are added, causing the cache to keep
growing ...
Nscd is also being used for dns-caching, which doesn't help, but I'm not
sure if that is the problem as sofia_dig seems to return valid values
(except maybe ttl).


 I would think that ttl is never touched and that the cached is cleared
when the ttl expires, but I have no idea when the dns-cache is cleared in
FS...

I know this is maybe a lot of text, but any info on this topic (sofia dns
cache) is welcome.

Thanks,

Michel
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