前回はインストールから証明書の作成までを行いました。
今回は、設定ファイルについてです。

サーバ設定ファイル

サーバ側の設定ファイルを作成します。

C:\\Program Files\\OpenVPN\\sample-config 以下に設定のサンプルファイルがあります。
そこにあるserver.ovpnというサーバ用のサンプルファイルをC:\\Program Files\\OpenVPN\\config以下にコピーします。

このサンプルファイルを元に、設定を行います。
赤字が変更を加えた箇所です

---------------
#################################################
# Sample OpenVPN 2.0 config file for　　　　　　#
# multi-client server.　　　　　　　　　　　　　#
#　　　　　　　　　　　　　　　　　　　　　　　 #
# This file is for the server side #
# of a many-clients <-> one-server #
# OpenVPN configuration. #
# #
# OpenVPN also supports #
# single-machine <-> single-machine #
# configurations (See the Examples page #
# on the web site for more info). #
# #
# This config should work on Windows #
# or Linux/BSD systems. Remember on #
# Windows to quote pathnames and use #
# double backslashes, e.g.: #
# \"C:\\\\Program Files\\\\OpenVPN\\\\config\\\\foo.key\" #
# #
# Comments are preceded with \'#\' or \';\' #
#################################################

# 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 1194

# TCP or UDP server?
;proto tcp
proto udp


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


# \"dev tun\" will create a routed IP tunnel,
# \"dev tap\" will create an ethernet tunnel.
# Use \"dev tap\" if you are ethernet bridging.
# 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 tap
;dev tun

# 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.
;dev-node MyTap
dev-node tap-1

# 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).
ca ca.crt
cert server.crt
key server.key # 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 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.
server 10.8.0.0 255.255.255.0

# 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.
ifconfig-pool-persist ipp.txt

# 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

# 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 192.168.10.0 255.255.255.0\"
;push \"route 192.168.20.0 255.255.255.0\"

# 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:
;client-config-dir ccd
;route 192.168.40.128 255.255.255.248
# Then create a file ccd/Thelonious with this line:
# iroute 192.168.40.128 255.255.255.248
# This will allow Thelonious\' private subnet to
# access the VPN. This example will only work
# if you are routing, not bridging, i.e. you are
# using \"dev tun\" and \"server\" directives.

# 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
# the TUN/TAP interface to the internet in
# order for this to work properly).
# CAVEAT: May break client\'s network config if
# client\'s local DHCP server packets get routed
# through the tunnel. Solution: make sure
# client\'s local DHCP server is reachable via
# a more specific route than the default route
# of 0.0.0.0/0.0.0.0.
;push \"redirect-gateway\"

# Certain Windows-specific network settings
# can be pushed to clients, such as DNS
# or WINS server addresses. CAVEAT:
# http://openvpn.net/faq.html#dhcpcaveats
;push \"dhcp-option DNS 10.8.0.1\"
;push \"dhcp-option WINS 10.8.0.1\"

# 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.
comp-lzo

# The maximum number of concurrently connected
# clients we want to allow.
;max-clients 100

# 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
;group nobody

# 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
persist-tun

# Output a short status file showing
# current connections, truncated
# and rewritten every minute.
status openvpn-status.log

# 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).
;log openvpn.log
;log-append openvpn.log

# 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 3

# Silence repeating messages. At most 20
# sequential messages of the same message
# category will be output to the log.
;mute 20

---------------
設定ファイルのダウンロード
以上の箇所を変更するだけで

使用プロトコル：UDP
ポート番号：1194
10.8.0.0/255.255.255.0 のサブネット
圧縮、Blowfish暗号、TLS認証等を有効にしたVPNが出来上がります。

詳細な設定項目はOpenVPN HOWTOで確認してください。


クライアント設定ファイル

クライアントPCで使用する設定ファイルを作成します。

クライアントPCの C:\\Program Files\\OpenVPN\\sample-config 以下に
設定のサンプルファイルがあります。
そこにclient.ovpnというクライアント用のサンプルファイルがあるのでC:\\Program Files\\OpenVPN\\config以下にコピーします。

このサンプルファイルを元に、設定を行います。
赤字が変更を加えた箇所です


##############################################
# Sample client-side OpenVPN 2.0 config file #
# for connecting to multi-client server. #
# #
# This configuration can be used by multiple #
# clients, however each client should have #
# its own cert and key files. #
# #
# On Windows, you might want to rename this #
# file so it has a .ovpn extension #
##############################################

# Specify that we are a client and that we
# will be pulling certain config file directives
# from the server.
tls-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 MyTap
dev-node tap-1

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

#OpenVPNが提供するDHCPサーバからIPアドレスの設定を受信
pull
float

# The hostname/IP and port of the server.
# You can have multiple remote entries
# to load balance between the servers.
remote 接続先サーバのホスト名（DDNS名） 1194
;remote my-server-2 1194

# 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.
persist-key
persist-tun

# 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

# 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 ca.crt
cert クライアント名.crt
key クライアント名.key


# 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.
ns-cert-type server

# 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 x
cipher BF-CBC

# 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

# Silence repeating messages
;mute 20

---------------------------
設定ファイルのダウンロード
以上で設定ファイルの記述は終了です。


証明書ファイルの配置

前回作成した証明書や鍵ファイルは、設定ファイルと同じディレクトリに置き直す必要があります。

作成した証明書はC:\\Program Files\\OpenVPN\\easy-rsa\\keys に
保存されてあるのでそこからC:\\Program Files\\OpenVPN\\config 以下に
コピーします。

サーバ側で必要なファイルは
ca.crt, server.crt, server.key, dh1024.pem, ta.keyの5つです。

クライアント側で必要なファイルは
ca.crt, クライアント名.crt, クライアント名.key, ta.keyの4つです。

クライアントに証明書を送る際には、USBメモリを利用するなどの安全な手段を利用してください。

サーバの自動起動の設定

コマンドプロンプトを起動し、
cd C:\\Program Files\\OpenVPN\\config と入力します。
openvpn server.ovpn を実行し、エラーが出ないことを確認してからF4キーを押して、コマンドプロンプトを終了します。

コントロールパネルから → 管理ツール → サービス と移動し
OpenVPN Serviceを探します。



スタートアップの種類を自動に変更すると、再起動時に自動でOpenVPNサービスが開始されます。

ブロードバンドルータなどの設定

外部ネットワークから接続を受け付けるためには
ブロードバンドルータなどの設定を変更して外部から来たUDPプロトコルの1194番ポートあてパケットが、サーバPCに届くようにポート転送設定する必要があります。

詳細はブロードバンドルータなどのマニュアルを参照してください。

クライアントの接続

C:\\Program Files\\OpenVPN\\config以下に
設定ファイルと証明書類が保存されていれば、タスクバーにある
OpenVPNのGUIクライアントをダブルクリックするだけでサーバに接続ができます。切断するときは右クリックをしてDisconnectを選択します。


VPNセッションの完成

以上で設定が全て完了しました。
今回の設定では
サーバにはIPアドレス 10.8.0.1が
クライアントにはIPアドレス 10.8.0.2が
割り当てられています。
クライアントのIPアドレス割り当て状況は
サーバのC:\\Program Files\\OpenVPN\\config\\ipp.txt で確認できます。

また、コマンドプロンプトでpingを行って、両方の接続の確認をしてください。

サーバ側のネットワーク共有フォルダを利用したいときには



このように入力すると利用できます。

今回の設定では、デフォルトゲートウェイやDNS情報等の書き換えを
行わないので、純粋にサーバPCへの安全なコネクションとして利用でき、
出先からの接続が便利になります。

複数のクライアントからサーバへ接続を行いたい時には、クライアントごとに証明書や鍵を作成して、クライアント用の接続設定を行ってください。