PHP LDAP 连接无法联系 LDAP 服务器

我有一个正在迁移的外部 Web 服务器。我正在尝试通过LDAP对内部服务器上的活动目录进行身份验证。我能够使用相同的代码从旧服务器(Ubuntu 8(连接和进行身份验证，但无法在新服务器(Redhat 7(上进行身份验证。

外部服务器当前运行的是 PHP 5.4.16 的 Redhat 7，并启用了 LDAP 支持 (php-ldap(。

内部服务器目前是带有LDAP和Active Directory的Windows Server 2008盒子。

下面的代码是我正在使用的当前PHP，它能够在旧服务器上连接，但在新服务器上出现问题。它基本上使用 PHP LDAP 连接字符串并尝试绑定。我已将一些个人信息替换为标识符。(用户名，子域名等(

<?php
$adServer = "ldaps://subdomain.domain.edu";
$ldap = ldap_connect($adServer);
$username = 'USERNAME';
$password = 'PASS';
$ldaprdn = 'DOMAIN' . "''" . $username;
ldap_set_option($ldap, LDAP_OPT_PROTOCOL_VERSION, 3);
ldap_set_option($ldap, LDAP_OPT_REFERRALS, 0);
$bind = @ldap_bind($ldap, $ldaprdn, $password);

if ($bind) {
    $filter="(sAMAccountName=$username)";
    $result = ldap_search($ldap,"dc=subdomain,dc=domain,dc=edu",$filter);
    ldap_sort($ldap,$result,"sn");
    $info = ldap_get_entries($ldap, $result);
    for ($i=0; $i<$info["count"]; $i++)
    {
        if($info['count'] > 1)
            break;
        echo "<p>You are accessing <strong> ". $info[$i]["sn"][0] .", " . $info[$i]["givenname"][0] ."</strong><br /> (" . $info[$i]["samaccountname"][0] .")</p>'n";
        echo '<pre>';
        var_dump($info);
        echo '</pre>';
        $userDn = $info[$i]["distinguishedname"][0];
    }
    @ldap_close($ldap);
} else {
    $msg = "Invalid email address / password";
    echo $msg;
}
?>

在新服务器上，我可以使用以下ldapsearch命令很好地连接到ldap服务器：

ldapsearch -x -LLL -h sub-domain.domain.edu -D 'CN=DOMAIN'USERNAME' -w 'PASS' -b "dc=subdomain,dc=domain,dc=edu" -s sub "(objectClass=user)" givenName

这是我的ldap.conf文件(/etc/openldap/ldap.conf，新服务器(

#
# LDAP Defaults
#
# See ldap.conf(5) for details
# This file should be world readable but not world writable.
#BASE   dc=example,dc=com
#URI    ldap://ldap.example.com ldap://ldap-master.example.com:666
#SIZELIMIT      12
#TIMELIMIT      15
#DEREF          never
#TLS_CACERTDIR  /etc/openldap/certs
# Turning this off breaks GSSAPI used with krb5 when rdns = false
SASL_NOCANON    on
TLS_REQCERT never

这是我在错误日志(新服务器(中得到的内容：

ldap_create
ldap_url_parse_ext(ldaps://subdomain.domain.edu)
ldap_bind_s
ldap_simple_bind_s
ldap_sasl_bind_s
ldap_sasl_bind
ldap_send_initial_request
ldap_new_connection 1 1 0
ldap_int_open_connection
ldap_connect_to_host: TCP subdomain.domain.edu:636
ldap_new_socket: 10
ldap_prepare_socket: 10
ldap_connect_to_host: Trying XXX.18X.XX.19:636
ldap_pvt_connect: fd: 10 tm: -1 async: 0
attempting to connect:
connect errno: 13
ldap_close_socket: 10
ldap_new_socket: 10
ldap_prepare_socket: 10
ldap_connect_to_host: Trying XXX.18X.XX.24:636
ldap_pvt_connect: fd: 10 tm: -1 async: 0
attempting to connect:
connect errno: 13
ldap_close_socket: 10
ldap_new_socket: 10
ldap_prepare_socket: 10
ldap_connect_to_host: Trying XXX.18X.XX.41:636
ldap_pvt_connect: fd: 10 tm: -1 async: 0
attempting to connect:
connect errno: 13
ldap_close_socket: 10
ldap_new_socket: 10
ldap_prepare_socket: 10
ldap_connect_to_host: Trying 2002:XXXX:XXXX::XXXX:XXXX 636
ldap_pvt_connect: fd: 10 tm: -1 async: 0
attempting to connect:
connect errno: 13
ldap_close_socket: 10
ldap_err2string
[Mon Feb 23 15:20:28.689775 2015] [:error] [pid 12299] [client 10.25.XX.XX:53630] PHP Warning:  ldap_bind(): Unable to bind to server: Can't contact LDAP server in /var/www/html/index2.php on line 19