(Fri May 23 00:30:33 2014) [sssd] [service_send_ping] (4): Pinging LDAP

(Fri May 23 00:30:33 2014) [sssd] [service_send_ping] (4): Pinging nss

(Fri May 23 00:30:33 2014) [sssd] [service_send_ping] (4): Pinging pam

(Fri May 23 00:30:33 2014) [sssd] [ping_check] (4): Service LDAP replied to ping

(Fri May 23 00:30:33 2014) [sssd] [ping_check] (4): Service pam replied to ping

(Fri May 23 00:30:33 2014) [sssd] [ping_check] (4): Service nss replied to ping

I see that based on timeout setting, there is 10 secs timeout setting. What exactly does Pinging LDAP do? because i dont see any packets coming thru the line using tcpdump from the hosts listed in the URI. 

Thanks