Hướng dẫn cấu hình OpenVPN Client to Site xác thưc qua token.

[Voyage]

Mình mới tìm hiểu về OpenVPN trên Ubuntu nên muốn đưa ra để mọi người có thể góp ý, bổ sung nhằm giúp mình và mọi người hiểu hơn về giải pháp này.

Đầu tiên mình xin đưa ra nhận xét của mình về OpenVPN: đơn giản, nhiều tùy chọn bảo mật cao, cộng đồng sử dụng lớn. Không chỉ đơn giản khi cấu hình mạng, mà còn rất linh hoạt với nhiều tùy chọn có sẵn trong file cấu hình VPN. Bạn cũng có thể lựa nhiều thuật toán mã hóa, tất cả các thuật toán mã hóa có thể được kiểm tra qua command: "openvpn --show-ciphers". Ngoài ra OpenVPN còn cho phép lựa chọn phương thức xác thực, ví dụ như dùng Cert tự sinh trên Server hoặc dùng Cert lưu trong token (cực kì bảo mật, cái này mình rất thích)...Và với cộng đồng tuyệt vời của OpenVPN, bất kì lỗi gì bạn gặp phải đều có thể nhận được sự giúp đỡ từ các thành viên trên diễn đàn.


Nếu bạn muốn hiểu hết các option có trong OpenVPN, hãy truy cập vào Website:
http://openvpn.net/index.php/open-source/documentation/howto.html


Hôm nay mình sẽ chia sẻ với mọi người bài lab dạng VPN Client-to-Site giúp người dùng có thể truy cập vào mạng nội bộ công ty từ Internet qua kết nối OpenVPN và sử dụng xác thực bằng token.
Mô hình mình chọn rất đơn giản như sau:
User----Internet-----Router-----OpenVPN Server---Local Network

1. Cấu hình trên Server: (chạy Linux, mình chọn Ubuntu)

Cài đặt: apt-get install openvpn
Lấy file cấu hình mẫu: /usr/share/doc/openvpn/examples/sample-config-files/server.conf.gz
Sửa file cấu hình có dạng như sau:
​

[INDENT]# Which local IP address should OpenVPN
# listen on? (optional)
;local a.b.c.d


# Which TCP/UDP port should OpenVPN listen on?
# If you want to run multiple OpenVPN instances
# on the same machine, use a different port
# number for each one.  You will need to
# open up this port on your firewall.

port 1195

# TCP or UDP server?[/INDENT]
[INDENT]proto tcp

# "dev tun" will create a routed IP tunnel,
# "dev tap" will create an ethernet tunnel.
# Use "dev tap0" if you are ethernet bridging
# and have precreated a tap0 virtual interface
# and bridged it with your ethernet interface.
# If you want to control access policies
# over the VPN, you must create firewall
# rules for the the TUN/TAP interface.
# On non-Windows systems, you can give
# an explicit unit number, such as tun0.
# On Windows, use "dev-node" for this.
# On most systems, the VPN will not function
# unless you partially or fully disable
# the firewall for the TUN/TAP interface
dev tun

[/INDENT]
[INDENT]
# Windows needs the TAP-Win32 adapter name
# from the Network Connections panel if you
# have more than one.  On XP SP2 or higher,
# you may need to selectively disable the
# Windows firewall for the TAP adapter.
# Non-Windows systems usually don't need this.
[/INDENT]
[INDENT]dev-node VPN

# SSL/TLS root certificate (ca), certificate
# (cert), and private key (key).  Each client
# and the server must have their own cert and
# key file.  The server and all clients will
# use the same ca file.
#
# See the "easy-rsa" directory for a series
# of scripts for generating RSA certificates
# and private keys.  Remember to use
# a unique Common Name for the server
# and each of the client certificates.
#
# Any X509 key management system can be used.
# OpenVPN can also use a PKCS #12 formatted key file
# (see "pkcs12" directive in man page).
[/INDENT]
[INDENT]ca /etc/openvpn/csuser/CAChain.pem[/INDENT]
[INDENT]cert /etc/openvpn/csuser/OpenVPN.pem
[/INDENT]
[INDENT]key /etc/openvpn/csuser/OpenVPN.pem # This file should be kept secret

# Diffie hellman parameters.
# Generate your own with:
#   openssl dhparam -out dh1024.pem 1024
# Substitute 2048 for 1024 if you are using
# 2048 bit keys.
dh /etc/openvpn/csuser/dh1024.pem

# Configure server mode and supply a VPN subnet
# for OpenVPN to draw client addresses from.
# The server will take 10.8.0.1 for itself,
# the rest will be made available to clients.
# Each client will be able to reach the server
# on 10.8.0.1. Comment this line out if you are
# ethernet bridging. See the man page for more info.
[/INDENT]
[INDENT]server 10.8.0.0 255.255.0.0

# Maintain a record of client  virtual IP address
# associations in this file.  If OpenVPN goes down or
# is restarted, reconnecting clients can be assigned
# the same virtual IP address from the pool that was
# previously assigned.
[/INDENT]
[INDENT]ifconfig-pool-persist ipp.txt

[/INDENT]
[INDENT]# Configure server mode for ethernet bridging.
# You must first use your OS's bridging capability
# to bridge the TAP interface with the ethernet
# NIC interface.  Then you must manually set the
# IP/netmask on the bridge interface, here we
# assume 10.8.0.4/255.255.255.0.  Finally we
# must set aside an IP range in this subnet
# (start=10.8.0.50 end=10.8.0.100) to allocate
# to connecting clients.  Leave this line commented
# out unless you are ethernet bridging.
;server-bridge 10.8.0.4 255.255.255.0 10.8.0.50 10.8.0.100

# Configure server mode for ethernet bridging
# using a DHCP-proxy, where clients talk
# to the OpenVPN server-side DHCP server
# to receive their IP address allocation
# and DNS server addresses.  You must first use
# your OS's bridging capability to bridge the TAP
# interface with the ethernet NIC interface.
# Note: this mode only works on clients (such as
# Windows), where the client-side TAP adapter is
# bound to a DHCP client.
;server-bridge

# Push routes to the client to allow it
# to reach other private subnets behind
# the server.  Remember that these
# private subnets will also need
# to know to route the OpenVPN client
# address pool (10.8.0.0/255.255.255.0)
# back to the OpenVPN server.


push "route 192.168.0.0 255.255.0.0"

# To assign specific IP addresses to specific
# clients or if a connecting client has a private
# subnet behind it that should also have VPN access,
# use the subdirectory "ccd" for client-specific
# configuration files (see man page for more info).

# EXAMPLE: Suppose the client
# having the certificate common name "Thelonious"
# also has a small subnet behind his connecting
# machine, such as 192.168.40.128/255.255.255.248.
# First, uncomment out these lines:

[/INDENT]
[INDENT]client-config-dir ccdcsuser[/INDENT]
[INDENT]ccd-exclusive

# EXAMPLE: Suppose you want to give
# Thelonious a fixed VPN IP address of 10.9.0.1.
# First uncomment out these lines:
;client-config-dir ccd
;route 10.9.0.0 255.255.255.252
# Then add this line to ccd/Thelonious:
#   ifconfig-push 10.9.0.1 10.9.0.2


# Suppose that you want to enable different
# firewall access policies for different groups
# of clients.  There are two methods:
# (1) Run multiple OpenVPN daemons, one for each
#     group, and firewall the TUN/TAP interface
#     for each group/daemon appropriately.
# (2) (Advanced) Create a script to dynamically
#     modify the firewall in response to access
#     from different clients.  See man
#     page for more info on learn-address script.
;learn-address ./script


# If enabled, this directive will configure
# all clients to redirect their default
# network gateway through the VPN, causing
# all IP traffic such as web browsing and
# and DNS lookups to go through the VPN
# (The OpenVPN server machine may need to NAT
# or bridge the TUN/TAP interface to the internet
# in order for this to work properly).
;push "redirect-gateway def1 bypass-dhcp"


# Certain Windows-specific network settings
# can be pushed to clients, such as DNS
# or WINS server addresses.  CAVEAT:
# http://openvpn.net/faq.html#dhcpcaveats
# The addresses below refer to the public
# DNS servers provided by opendns.com.
push "dhcp-option DNS 192.168.10.123"
;push "dhcp-option DNS 208.67.220.220"


# Uncomment this directive to allow different
# clients to be able to "see" each other.
# By default, clients will only see the server.
# To force clients to only see the server, you
# will also need to appropriately firewall the
# server's TUN/TAP interface.
;client-to-client


# Uncomment this directive if multiple clients
# might connect with the same certificate/key
# files or common names.  This is recommended
# only for testing purposes.  For production use,
# each client should have its own certificate/key
# pair.
#
# IF YOU HAVE NOT GENERATED INDIVIDUAL
# CERTIFICATE/KEY PAIRS FOR EACH CLIENT,
# EACH HAVING ITS OWN UNIQUE "COMMON NAME",
# UNCOMMENT THIS LINE OUT.
;duplicate-cn


# The keepalive directive causes ping-like
# messages to be sent back and forth over
# the link so that each side knows when
# the other side has gone down.
# Ping every 10 seconds, assume that remote
# peer is down if no ping received during
# a 120 second time period.
keepalive 10 120


# For extra security beyond that provided
# by SSL/TLS, create an "HMAC firewall"
# to help block DoS attacks and UDP port flooding.
#
# Generate with:
#   openvpn --genkey --secret ta.key
#
# The server and each client must have
# a copy of this key.
# The second parameter should be '0'
# on the server and '1' on the clients.
;tls-auth ta.key 0 # This file is secret
# Select a cryptographic cipher.
# This config item must be copied to
# the client config file as well.
;cipher BF-CBC        # Blowfish (default)
;cipher AES-128-CBC   # AES
cipher DES-EDE3-CBC  # Triple-DES


# Enable compression on the VPN link.
# If you enable it here, you must also
# enable it in the client config file.








[/INDENT]
[INDENT]comp-lzo

# The maximum number of concurrently connected
# clients we want to allow.
max-clients 300
[/INDENT]
[INDENT]
[/INDENT]
[INDENT]# It's a good idea to reduce the OpenVPN
# daemon's privileges after initialization.
#
# You can uncomment this out on
# non-Windows systems.
user nobody[/INDENT]
[INDENT]group nogroup[/INDENT]
[INDENT]
#Check Serial in token via script
tls-verify verify-cn

# The persist options will try to avoid
# accessing certain resources on restart
# that may no longer be accessible because
# of the privilege downgrade.
persist-key
[/INDENT]
[INDENT]persist-tun

# Output a short status file showing
# current connections, truncated
# and rewritten every minute.
# By default, log messages will go to the syslog (or
# on Windows, if running as a service, they will go to
# the "\Program Files\OpenVPN\log" directory).
# Use log or log-append to override this default.
# "log" will truncate the log file on OpenVPN startup,
# while "log-append" will append to it.  Use one
# or the other (but not both).

[/INDENT]
[INDENT]log        /etc/openvpn/vpncsuser.log[/INDENT]
[INDENT]log-append  openvpn-server.log

status status.log 5
status-version 2[/INDENT]
[INDENT]
# Set the appropriate level of log
# file verbosity.
#
# 0 is silent, except for fatal errors
# 4 is reasonable for general usage
# 5 and 6 can help to debug connection problems
# 9 is extremely verbose
verb 4
[/INDENT]

Chú ý: Phải mở Port 1195 trên Firewall, với mô hình trên thì cần mở Port trên chính Server VPN.​

Mọi người nên đọc tất cả các dòng comment trong file cấu hình để hiểu các option trong file cấu hình nhé

​

1. Cấu hình Router: NAT Port 1195 của Server VPN để Client có thể kết nối VPN tới Server.
2. Cấu hình Client có dạng:

# Specify that we are a client and that we
# will be pulling certain config file directives
# from the server.
client

# Use the same setting as you are using on
# the server.
# On most systems, the VPN will not function
# unless you partially or fully disable
# the firewall for the TUN/TAP interface.
;dev tap
dev tun

# Windows needs the TAP-Win32 adapter name
# from the Network Connections panel
# if you have more than one.  On XP SP2,
# you may need to disable the firewall
# for the TAP adapter.
dev-node VPN

# Are we connecting to a TCP or
# UDP server?  Use the same setting as
# on the server.
;proto udp

proto tcp

# The hostname/IP and port of the server.
# You can have multiple remote entries
# to load balance between the servers.
remote [IP Public hoặc domain của Server VPN] 1195

# Choose a random host from the remote
# list for load-balancing.  Otherwise
# try hosts in the order specified.
;remote-random

# Keep trying indefinitely to resolve the
# host name of the OpenVPN server.  Very useful
# on machines which are not permanently connected
# to the internet such as laptops.

resolv-retry infinite

# Most clients don't need to bind to
# a specific local port number.
nobind

# Downgrade privileges after initialization (non-Windows only)
;user nobody
;group nobody

# Try to preserve some state across restarts.

# If you are connecting through an
# HTTP proxy to reach the actual OpenVPN
# server, put the proxy server/IP and
# port number here.  See the man page
# if your proxy server requires
# authentication.
;http-proxy-retry # retry on connection failures
;http-proxy [proxy server] [proxy port #]


# Wireless networks often produce a lot
# of duplicate packets.  Set this flag
# to silence duplicate packet warnings.
;mute-replay-warnings




persist-key
persist-tun

# SSL/TLS parms.
# See the server config file for more
# description.  It's best to use
# a separate .crt/.key file pair
# for each client.  A single ca
# file can be used for all clients.

ca "C:\\Program Files\\OpenVPN\\config\\CAChain.pem"

# Verify server certificate by checking
# that the certicate has the nsCertType
# field set to "server".  This is an
# important precaution to protect against
# a potential attack discussed here:
#  http://openvpn.net/howto.html#mitm
#
# To use this feature, you will need to generate
# your server certificates with the nsCertType
# field set to "server".  The build-key-server
# script in the easy-rsa folder will do this

# If a tls-auth key is used on the server
# then every client must also have the key.
;tls-auth ta.key 1


# Select a cryptographic cipher.
# If the cipher option is used on the server
# then you must also specify it here.

cipher DES-EDE3-CBC  # Triple-DES

# Enable compression on the VPN link.
# Don't enable this unless it is also
# enabled in the server config file.
comp-lzo

# Set log file verbosity.
verb 3


route-method exe
route-delay 5 30
tap-sleep 5[INDENT]
[/INDENT]
pkcs11-providers "C:\\Windows\\System32\\eToken.dll"
pkcs11-id 
'Aladdin\x20Knowledge\x20Systems\x20Ltd\x2E/eToken/006b53f3/eToken/44393535424236302D46453938******************************************'

Vậy là việc cấu hình đã hoàn thiện, mọi người cần chú ý tới cấu hình mạng trong những mô hình phức tạp, nhiều thiết bị định tuyển.


​

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AD cho em hỏi, em đã setup được openvpn server và kết nối từ client thành công trên window, ad có thể tư vấn giúp em cách sử dụng thêm google authentication để xác thực 2 yếu tố cho openVPN server này được không ạ ? Em cảm ơn