Problems can arise if a firewall is placed between WebSphere Portal Server and the chosen LDAP directory server. Under such circumstances, authentication can appear to stall after a long period of inactivity. This typically manifests itself in the morning after a night of inactivity,whereupon users may wait up to 30 minutes before authenticating into the Portal solution (unless the Portal is restarted or the LDAP Reuse Connection parameter is disabled from the WebSphere administrative console and WMM connection pooling mechanism is disabled).
After this initial period, subsequent users are authenticated in the normal fashion.
The origin of this problem is not with WebSphere Portal Server or the underlying WebSphere Application Server instance, but with the firewall idle timeout. System Administrators should ensure that the tcp_keepidle system setting on each of the servers is smaller than the firewall idle timeout. Failing this, when a client is left to idle for longer than the firewall idle timeout, a communications error will be encountered. Usually, a keepAlive packet is sent according to the tcp setting of tcp_keepidle.