connect() returns EADDRINUSE during massive host->host conn rate

Ivan Voras ivoras at
Wed Nov 28 10:39:44 PST 2007

Jan Srzednicki wrote:
> Hello,
> I have a pair of hosts. One of them performs a massive amount of
> TCP connections to the other one, all to the same port. This setup
> mostly works fine, but from time to time (that varies, from once a
> minute to one a half an hour), the connect(2) syscall fails with 
> EADDRINUSE. The connection rate tops to 50 connection
> initiations/second.

This looks like the old (and probably well known) problem "ab" has.
("ab" is "apache benchmark", a utility which is bundled with apache and
which does repeated connections to the specified address, does
transactions and computes some statistics). AFAIK this behaviour was
present since at least 5.2, maybe earlier. No known fixes.

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