nss_ldap and ping not working

I found out that the nss_ldap queries works with
    getent hosts xyz
but not with
    ping xyz

ping (and e.g. traceroute) hangs somewhere within
ldap_init
( libnss_ldap with debugging stops after: "nss_ldap: ==> ldap_init" )
and futex
( strace stops at "futex(0x375a8c, FUTEX_WAIT, 2, NULL" )

This is the same for known and unknown hosts.

Other programs work just fine: telnet rsh arping ssh ...
(but ssh outputs a warning "socket: Address family not supported by protocol" )

regards,
Herbert Gasiorowski
http://www.mathematik.uni-marburg.de/~gasi/