request drops in BIND?

[Barry Margolin]

In article <c7o2j0$845$1 at sf1.isc.org>,
 KyoungSoo Park <kyoungso at cs.princeton.edu> wrote:

> Hi BIND hackers(or anyone interested in BIND's performance),
> 
> To know BIND's reliability & performance, I tested BIND 9.2.3 by sending 
> burst requests and
> seeing how many actually get back.
> When I did 200 requests of a single local domain name(the result should 
> be cached in the BIND) at the same time,
> I see about 20 - 22 responses are usually missing.
> 
> The BIND server that I configured is for testing only, so there is no 
> user except for me.
> I wonder why it starts failing to respond at the burst request rate 178 
> requests/sec.
> When I looked through tcpdump, then it seems the BIND gets all requests, but
> it seems it's dropping requests inside the server.

Are you sure about that?  It could be getting dropped in the UDP stack 
*after* tcpdump has reported that the packet was received.  You should 
enable BIND's debugging -- if it intentionally drops a request, I would 
expect it to log a debugging message.

When we were having performance problems on our caching nameservers, we 
noticed that queries to the virtual address that we publicized to our 
customers would frequently time out, but queries sent to the server's 
"real" address would have no problems.  So the problem was that the 
per-socket buffer was overflowing (BIND uses a separate UDP socket for 
each of the server's addresses).

-- 
Barry Margolin, barmar at alum.mit.edu
Arlington, MA
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