PHP Warning: ldap_bind(): Unable to bind to server: Can't contact LDAP server

Had this error on RHEL7 ( CentOS7 ) due to SELinux restricting ports HTTPD can use.

LDAP ports 389 and 636 are not on the default allow list, you can unblock with:

setsebool -P httpd_can_network_connect 1

You can test for the restriction by trying a socket to the LDAP server:

fsockopen('LDAP-Server-IP', 389);

It will give 'Permission Denied' showing it's blocked and not a credentials issue.

Also check your SELinux audit log file for other things being blocked.

Connect opens the session. Bind is what actually authenticates you. Thus you connected but did not login with valid credentials.