Using iRedMail And OpenVPN For Virtual Email Hosting And VPN Services, With Central Authentication Against OpenLDAP (CentOS 5.4)

iRedMail is a shell script that lets you quickly deploy a full-featured mail solution in less than 2 minutes. iRedMail supports both OpenLDAP and MySQL as backends for storing virtual domains and users.

This tutorial shows you how to integrate OpenVPN into iredmail's ldap backend on CentOS 5.x, Let openvpn auth OpenLDAP，passwords will be stored in ldap and you can change the password though webmail.

This tutorial is based on CentOS 5.4, so I suggest set up a minimum CentOS 5.4 system, install iredmail 0.6 and choose openldap as the backend, as shown in these tutorials:

• iRedMail: Mail Server With LDAP, Postfix, RoundCube/SquirrelMail, Dovecot, ClamAV, SpamAssassin, Amavisd (Debian 5.0.1)
• iRedMail: Build A Full-Featured Mail Server With LDAP, Postfix, RoundCube, Dovecot, ClamAV,SpamAssassin, DKIM, SPF On CentOS 5.x

1 Install OpenVPN

Use the EPEL yum repository to install OpenVPN.

rpm -Uhv http://download.fedora.redhat.com/pub/epel/5/i386/epel-release-5-3.noarch.rpm # <-- For i386
rpm -Uhv http://download.fedora.redhat.com/pub/epel/5/x86_64/epel-release-5-3.noarch.rpm # <-- For x86_64

Install OpenVPN and ldap support:

yum install openvpn openvpn-auth-ldap
chkconfig openvpn on

Install dnsmasq - to forward DNS traffic through the VPN you will need to install the dnsmasq package:

yum install dnsmasq
/etc/init.d/dnsmasq start
chkconfig dnsmasq on

2 easy-rsa

The OpenVPN package provides a set of encryption-related tools called "easy-rsa". These scripts are located by default in the /usr/share/doc/openvpn/examples/easy-rsa/ directory. However, in order to function properly, these scripts should be located in the /etc/openvpn directory. We also need to copy the Openvpn config example file to /etc/openvpn.

cp -R /usr/share/openvpn/easy-rsa/ /etc/openvpn

Configure Public Key Infrastructure Variables

Before we can generate the public key infrastructure for OpenVPN we must configure a few variables that the easy-rsa scripts will use to generate the scripts. These variables are set near the end of the /etc/openvpn/easy-rsa/2.0/vars file. Here is an example of the relevant values:

Edit /etc/openvpn/easy-rsa/2.0/vars:

export KEY_COUNTRY="CN" export KEY_PROVINCE="BJ" export KEY_CITY="BeiJing" export KEY_ORG="iredmail" export KEY_EMAIL="www@example.com"

Initialize the Public Key Infrastructure (PKI)

Issue the following commands in sequence to internalize the certificate authority and the public key infrastructure:

cd /etc/openvpn/easy-rsa/2.0/
chmod +rwx *
source ./vars
./clean-all
./pkitool --initca

Generate Certificates

With the certificate authority generated you can generate the private key for the server. This script will also prompt you for additional information. By default, the Common Name for this key will be "server". You can change these values in cases where it makes sense to use alternate values. To accomplish this, issue the following command:

./pkitool --server server

Generate Diffie Hellman Parameters Link

The "Diffie Hellman Parameters" govern the method of key exchange and authentication used by the OpenVPN server. Issue the following command to generate these parameters:

./build-dh

Relocate Secure Keys

The keys and certificates for the server need to be relocated to the /etc/openvpn directory so the OpenVPN server process can access them. These files are:

• ca.crt
• ca.key
• dh1024.pem
• server.crt
• server.key

cp keys/{ca.crt,ca.key,server.crt,server.key,dh1024.pem} /etc/openvpn/

These files no need leave your server. Maintaining integrity and control over these files is of the utmost importance to the integrity of your server. If you ever need to move or back up these keys, ensure that they're encrypted and secured.

3 Configure OpenVPN support LDAP auth

Find cn=vmail password

The vmail password was randomly created during iredmail install. You can find the password in /etc/postfix/ldap_virtual_mailbox_domains.cf:

cat /etc/postfix/ldap_virtual_mailbox_domains.cf

bind_dn = cn=vmail,dc=example,dc=com bind_pw = InYTi8qGjamTb6Me2ESwbb6rxQUs5y #cn=vmail password

Configure LDAP auth in /etc/openvpn/auth/ldap.conf

# LDAP server URL

URL             ldap://localhost

# Bind DN (If your LDAP server doesn't support anonymous binds)

BindDN                cn=vmail,dc=example,dc=com

# Bind Password cn=vmail password

Password      InYTi8qGjamTb6Me2ESwbb6rxQUs5y

# Network timeout (in seconds)

Timeout         15

# Base DN

BaseDN          "o=domains,dc=example,dc=com"

# User Search Filter

SearchFilter    "(&(objectClass=mailUser)(accountStatus=active)(enabledService=vpn))"

# Require Group Membership

RequireGroup    false

4 Configuring OpenVPN

We'll now need to configure our server file. There is an example file in /usr/share/doc/openvpn-2.1.1/examples/sample-config-files. Issue the following sequence of commands to retrieve the example configuration files and move them to the required directories:

cp /usr/share/doc/openvpn-2.1.1/sample-config-files/server.conf /etc/openvpn/

Now edit /etc/openvpn/server.conf:

push "redirect-gateway def1" push "dhcp-option DNS 10.8.0.1" plugin /usr/lib/openvpn/plugin/lib/openvpn-auth-ldap.so /etc/openvpn/auth/ldap.conf client-cert-not-required

5 Enable VPN service for mail user

Use phpLDAPadmin or other tools to add sample LDAP attributes and values for existing mail users.

Log into phpLDAPadmin:

Find the existing mail user www@example.com:

Enable the VPN service for the user www@example.com:

6 Enable IP forward and config iptables

Edit the /etc/sysctl.conf file to modify the following line to ensure that your system is able to forward IPv4 traffic:

net.ipv4.ip_forward = 1

Issue the following command to configure iptables to properly forward traffic through the VPN:

echo 1 > /proc/sys/net/ipv4/ip_forward

Edit the /etc/sysconfig/iptables file and add the below. Open port 1194.

#openvpn

-A INPUT -p udp -m multiport --dport 1194 -j ACCEPT

Issue the following commands to set this variable for the current session:

iptables -A FORWARD -m state --state RELATED,ESTABLISHED -j ACCEPT
iptables -A FORWARD -s 10.8.0.0/24 -j ACCEPT
iptables -A FORWARD -j REJECT
iptables -t nat -A POSTROUTING -s 10.8.0.0/24 -o eth0 -j MASQUERADE

Before continuing, insert these iptables rules into your system's /etc/rc.local file to ensure that theses iptables rules will be recreated following your next reboot cycle:

#!/bin/sh

#

# [...]

#

iptables -A FORWARD -m state --state RELATED,ESTABLISHED -j ACCEPT

iptables -A FORWARD -s 10.8.0.0/24 -j ACCEPT

iptables -A FORWARD -j REJECT

iptables -t nat -A POSTROUTING -s 10.8.0.0/24 -o eth0 -j MASQUERADE

touch /var/lock/subsys/local

7 Restart related services

We need to restart all related services to make the new configuration work:

/etc/init.d/ldap restart
/etc/init.d/openvpn restart
/etc/init.d/iptables restart

8 Client setting

cp /usr/share/doc/openvpn-2.1.1/sample-config-files/client.conf /etc/openvpn/easy-rsa/2.0/keys/client.ovpn
cd /etc/openvpn/easy-rsa/2.0/keys

Edit the client.ovpn file to modify the following line:

# Add the vpn server remote mail.example.com 1194 #Comment out the below two line #cert client.crt #key client.key #Add thes line at the botton auth-user-pass

Copy the client.ovpn and ca.crt file to your client system. Also you can use mutt to send the files to your mailbox. You can log in to your email account and download the files.

yum -y install mutt zip
cd /etc/openvpn/easy-rsa/2.0/keys
zip config.zip client.ovpn ca.crt
mutt -s "OpenVPN client config files" -a /etc/openvpn/easy-rsa/2.0/keys/config.zip www@example.com < /usr/share/doc/openvpn-2.1.1/README

Installing OpenVPN GUI On Windows XP / Vista

Download the client software here: http://www.openvpn.se/development.html. The tested version is OpenVPN 2.1_beta7 & OpenVPN GUI 1.0.3, it works on Vista. After the installation, put the client.ovpn and ca.crt file to C:\Program Files\OpenVPN\config.

Now you can use the account www@example.com to connect to the vpn.

9 Troubleshooting

Enable logging in ldap:

vi /etc/ldap/slapd.conf

loglevel 256 # <-- change from 0 to 256

Enable the Openvpn log:

Issue the following commands to create log files and set the right permissions:

touch /var/log/openvpn.log
touch /var/log/openvpn-status.log
chown nobody.nobody /var/log/openvpn.log
chown nobody.nobody /var/log/openvpn-status.log

Edit /etc/openvpn/server.conf:

user nobody group nobody status /var/log/openvpn-status.log log /var/log/openvpn.log

Monitor the log:

tail -0f /var/log/openldap.log

Apr 4 22:45:17 centos54 slapd[6622]: conn=0 fd=14 ACCEPT from IP=127.0.0.1:35456 (IP=0.0.0.0:389)
Apr 4 22:45:17 centos54 slapd[6622]: conn=0 op=0 BIND dn="cn=vmail,dc=example,dc=com" method=128
Apr 4 22:45:17 centos54 slapd[6622]: conn=0 op=0 BIND dn="cn=vmail,dc=example,dc=com" mech=SIMPLE ssf=0
Apr 4 22:45:17 centos54 slapd[6622]: conn=0 op=0 RESULT tag=97 err=0 text=
Apr 4 22:45:17 centos54 slapd[6622]: conn=0 op=1 SRCH base="o=domains,dc=example,dc=com"
scope=2 deref=0 filter="(&(objectClass=mailUser)(accountStatus=active)(enabledService=vpn))"
Apr 4 22:45:17 centos54 slapd[6622]: conn=1 fd=18 ACCEPT from IP=127.0.0.1:35457 (IP=0.0.0.0:389)
Apr 4 22:45:17 centos54 slapd[6622]: conn=0 op=1 SEARCH RESULT tag=101 err=0 nentries=1 text=
Apr 4 22:45:17 centos54 slapd[6622]: conn=1 op=0 BIND dn="cn=vmail,dc=example,dc=com" method=128
Apr 4 22:45:17 centos54 slapd[6622]: conn=1 op=0 BIND dn="cn=vmail,dc=example,dc=com" mech=SIMPLE ssf=0
Apr 4 22:45:17 centos54 slapd[6622]: conn=1 op=0 RESULT tag=97 err=0 text=
Apr 4 22:45:17 centos54 slapd[6622]: conn=1 op=1 BIND anonymous mech=implicit ssf=0
Apr 4 22:45:17 centos54 slapd[6622]: conn=1 op=1 BIND dn="mail=www@example.com,
ou=Users,domainName=example.com,o=domains,dc=example,dc=com" method=128
Apr 4 22:45:17 centos54 slapd[6622]: conn=1 op=1 BIND dn="mail=www@example.com,
ou=Users,domainName=example.com,o=domains,dc=example,dc=com" mech=SIMPLE ssf=0
Apr 4 22:45:17 centos54 slapd[6622]: conn=1 op=1 RESULT tag=97 err=0 text=
Apr 4 22:45:17 centos54 slapd[6622]: conn=0 op=2 UNBIND
Apr 4 22:45:17 centos54 slapd[6622]: conn=1 op=2 UNBIND
Apr 4 22:45:17 centos54 slapd[6622]: conn=1 fd=18 closed
Apr 4 22:45:17 centos54 slapd[6622]: conn=2 fd=18 ACCEPT from IP=127.0.0.1:35458 (IP=0.0.0.0:389)
Apr 4 22:45:17 centos54 slapd[6622]: conn=2 op=0 BIND dn="cn=vmail,dc=example,dc=com" method=128
Apr 4 22:45:17 centos54 slapd[6622]: conn=2 op=0 BIND dn="cn=vmail,dc=example,dc=com" mech=SIMPLE ssf=0
Apr 4 22:45:17 centos54 slapd[6622]: conn=0 fd=14 closed
Apr 4 22:45:17 centos54 slapd[6622]: conn=2 op=0 RESULT tag=97 err=0 text=
Apr 4 22:45:17 centos54 slapd[6622]: conn=2 op=1 SRCH base="o=domains,dc=example,dc=com"
scope=2 deref=0 filter="(&(objectClass=mailUser)(accountStatus=active)(enabledService=vpn))"
Apr 4 22:45:17 centos54 slapd[6622]: conn=2 op=1 SEARCH RESULT tag=101 err=0 nentries=1 text=
Apr 4 22:45:17 centos54 slapd[6622]: conn=2 op=2 UNBIND
Apr 4 22:45:17 centos54 slapd[6622]: conn=2 fd=18 closed

tail -0f /var/log/openvpn.log

Sun Apr 4 22:47:01 2010 MULTI: multi_create_instance called
Sun Apr 4 22:47:01 2010 192.168.1.147:51240 Re-using SSL/TLS context
Sun Apr 4 22:47:01 2010 192.168.1.147:51240 LZO compression initialized
Sun Apr 4 22:47:01 2010 192.168.1.147:51240 Control Channel MTU parms [ L:1542 D:138 EF:38 EB:0 ET:0 EL:0 ]
Sun Apr 4 22:47:01 2010 192.168.1.147:51240 Data Channel MTU parms [ L:1542 D:1450 EF:42 EB:135 ET:0 EL:0 AF:3/1 ]
Sun Apr 4 22:47:01 2010 192.168.1.147:51240 Local Options hash (VER=V4): '530fdded'
Sun Apr 4 22:47:01 2010 192.168.1.147:51240 Expected Remote Options hash (VER=V4): '41690919'
Sun Apr 4 22:47:01 2010 192.168.1.147:51240 TLS: Initial packet from 192.168.1.147:51240, sid=01b29dca a4554de8
Sun Apr 4 22:47:01 2010 192.168.1.147:51240 PLUGIN_CALL:
POST /usr/lib/openvpn/plugin/lib/openvpn-auth-ldap.so/PLUGIN_AUTH_USER_PASS_VERIFY status=0
Sun Apr 4 22:47:01 2010 192.168.1.147:51240 TLS: Username/Password authentication succeeded for username 'www@example.com'
Sun Apr 4 22:47:01 2010 192.168.1.147:51240 Data Channel Encrypt: Cipher 'BF-CBC' initialized with 128 bit key
Sun Apr 4 22:47:01 2010 192.168.1.147:51240 Data Channel Encrypt: Using 160 bit message hash 'SHA1' for HMAC authentication
Sun Apr 4 22:47:01 2010 192.168.1.147:51240 Data Channel Decrypt: Cipher 'BF-CBC' initialized with 128 bit key
Sun Apr 4 22:47:01 2010 192.168.1.147:51240 Data Channel Decrypt: Using 160 bit message hash 'SHA1' for HMAC authentication
Sun Apr 4 22:47:01 2010 192.168.1.147:51240 Control Channel: TLSv1, cipher TLSv1/SSLv3 DHE-RSA-AES256-SHA
Sun Apr 4 22:47:01 2010 192.168.1.147:51240 [] Peer Connection Initiated with 192.168.1.147:51240
Sun Apr 4 22:47:01 2010 192.168.1.147:51240 PLUGIN_CALL:
POST /usr/lib/openvpn/plugin/lib/openvpn-auth-ldap.so/PLUGIN_CLIENT_CONNECT status=0
Sun Apr 4 22:47:01 2010 192.168.1.147:51240 MULTI: Learn: 10.8.0.14 -> 192.168.1.147:51240
Sun Apr 4 22:47:01 2010 192.168.1.147:51240 MULTI: primary virtual IP for 192.168.1.147:51240: 10.8.0.14
Sun Apr 4 22:47:02 2010 192.168.1.147:51240 PUSH: Received control message: 'PUSH_REQUEST'
Sun Apr 4 22:47:02 2010 192.168.1.147:51240 SENT CONTROL [UNDEF]:
'PUSH_REPLY,redirect-gateway def1,dhcp-option DNS 10.8.0.1,route 10.8.0.1,
topology net30,ping 10,ping-restart 120,ifconfig 10.8.0.14 10.8.0.13' (status=1)
Sun Apr 4 22:47:13 2010 192.168.1.147:51240 Authenticate/Decrypt
packet error: bad packet ID (may be a replay): [ #1 ] -- see the man page entry for
--no-replay and --replay-window for more info or silence this warning with --mute-replay-warnings

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