I set the connection timeout parameter to 0 to disable connection timeouts on the server.

This seems to have been the cause of all the connection "closed error 11 (Resource temporarily unavailable)" errors, which were in turn probably the cause of MacOS X boxes not being able to authenticate properly. The previous setting was 10 seconds, and the average idle time for connections that ended with this error was between 9 and 10 seconds (sometimes greater than that, but if we're talking about an alarm that a thread sets, then it could very well be greater, or it could also be that some sort of keepalive traffic had been sent but not logged in the access log).

Tue Jun 17 14:20

We haven't had any more errors in the LDAP logs and MacOS X logons are working consistently now.