Great Suggestion for the DNS problem...?

Mikael Abrahamsson swmike at
Tue Jul 29 16:21:49 UTC 2008

On Tue, 29 Jul 2008, Steven M. Bellovin wrote:

> In this situation, UDP uses one query packet and one reply.  TCP uses 3
> to set up the connection, a query, a reply, and three to tear down the
> connection.  *Plus* the name server will have to keep state for
> every client, plus TIMEWAIT state, etc.  (Exercise left to TCP geek
> readers: how few packets can you do this in?  For example -- send the
> query with the SYN+ACK, send client FIN with the query, send server FIN
> with the answer?  Bonus points for not leaving the server's side in
> TIMEWAIT.  Exercise for implementers: how sane can your stack be if
> you're going to support that?)

The bittorrent tracker guys seem to run into problems at around 30kk 
tracker requests per second (TCP), and they say it's mostly setup/teardown 
(sy usage in vmstat), the tracker hash lookup doesn't take that much.

They're trying to move to UDP, currently their workload is approx 5% UDP.

I guess TCP DNS workload would be similar in characteristics.

Mikael Abrahamsson    email: swmike at

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