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openvpn on centos7

bantana
1 July 2015

introduction

design

network topology:

internet ---- openvpn server ---10.8.2.0/24--- idc localnet
     |
     |(10.9.1.0/24)
     |
vpn clients

从network topology上看vpn client和openvpn server之间建立一个虚拟网段(10.9.1.0/24), 然后这个openvpn做为一个路由器,把10.8.2.0/24的网段和10.9.1.0/24的虚拟网段连接起来。

1. 用户需要异地登陆访问openvpn主机并建立一个虚拟网络;

2. idc内网只有内网ip的主机需要访问外网,同时内网tcp/ip数据包需要经过internet网络也需要做ip masq;

install

在centos7上安装openvpn需要安装epel-release库包

$ sudo yum -y install epel-release

然后需要安装openvpn包和easy-rsa用来管理证书的包

$ sudo yum -y install openvpn easy-rsa

config

# Which local IP address should OpenVPN
# listen on? (optional)
;local a.b.c.d
local 111.111.111.111

# 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

# "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 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

# 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 /etc/openvpn/keys/ca.crt
cert /etc/openvpn/keys/vpn.crt
key /etc/openvpn/keys/vpn.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 /etc/openvpn/keys/dh2048.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 10.9.1.0 255.255.255.0

# 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

# 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 192.168.1.0 255.255.255.0"
push "route 192.168.1.0 255.255.255.0"
push "route 192.168.2.0 255.255.255.0"
push "route 192.168.3.0 255.255.255.0"

# 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
route 192.168.1.0 255.255.255.0
route 192.168.2.0 255.255.255.0
route 192.168.3.0 255.255.255.0
;route 10.8.2.0 255.255.255.0

# 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
# or bridge the TUN/TAP interface to the internet
# in order for this to work properly).
;push "redirect-gateway def1 bypass-dhcp"
;push "redirect-gateway def1 bypass-dhcp"
;push "redirect-gateway def1"

# 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 202.106.0.20"
push "dhcp-option DNS 208.67.222.222"
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.
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

crl-verify /etc/openvpn/keys/crl.pem

下面重点提几个配置参数:

监听的ip:

local 111.111.111.111

监听的端口:

port 1194

使用udp协议:

proto udp

使用routed ip tunnel:

dev tun

证书:

ca /etc/openvpn/keys/ca.crt
cert /etc/openvpn/keys/vpn.crt
key /etc/openvpn/keys/vpn.key  # This file should be kept secret

Diffie hellman parameters:

dh /etc/openvpn/keys/dh2048.pem

vpn server 和 client之间的vpn subnet:

server 10.9.1.0 255.255.255.0

指定ip pool分配的ip对应表:

ifconfig-pool-persist ipp.txt

证书吊销状态, 后面会讲到如何生成:

crl-verify /etc/openvpn/keys/crl.pem

/etc/openvpn/ipp.txt

arrietty,10.9.1.4
zhaomm,10.9.1.8
chenmm,10.9.1.12
zhaoxm,10.9.1.16
gs3,10.9.1.20
gs2,10.9.1.24

每个ip tunnel需要消耗2个ip。

utun0: flags=8051<UP,POINTOPOINT,RUNNING,MULTICAST> mtu 1500
  inet 10.9.1.18 --> 10.9.1.17 netmask 0xffffffff

但从ipp.txt中看每次一个用户登录间隔4个ip。

certification

证书管理需要用到easy-rsa包

$ cp -rf /usr/share/easy-rsa/2.0 /etc/openvpn/easy-rsa

$ cd /etc/openvpn/easy-rsa

$ cp openssl-1.0.0.cnf openssl.cnf

根据你的情况修改下面几个参数:

$ vi vars

export KEY_COUNTRY="CN"
export KEY_PROVINCE="GD"
export KEY_CITY="SZ"
export KEY_ORG="aozsky"
export KEY_EMAIL="b@giiso.com"
export KEY_OU="server"

# X509 Subject Field
export KEY_NAME="EasyRSA"

做好上面的准备后,就可以开始管理证书了。

首次使用:

source ./vars
./clean-all    -> 这个会清除所有的证书和文件
./build-dh     -> 建立Diffie hellman文件
./pkitool --initca
./pkitool --server myserver
./pkitool client1
./pkitool --pass client2

上述命令会生成一个目录

/etc/openvpn/easy-rsa/keys

把这个目录link到/etc/openvpn/keys

$ cd /etc/openvpn
$ ln -s /etc/openvpn/easy-rsa/keys
生成一个test client,然后吊销:

 ./pkitool test
 ./revoke-full test

这个会生成下面的证书吊销状态文件:

/etc/openvpn/keys/crl.pem

以后管理的时候:

source ./vars
./pkitool client2

开启ip forward;

# sysctl -w net.ipv4.ip_forward=1

$ vi /etc/sysctl.conf

net.ipv4.ip_forward = 1

firewalld

firewall-cmd --list-all
firewall-cmd --add-masquerade

firewall-cmd --permanent --add-masquerade
firewall-cmd --query-masquerade
yes

other design

增加多个idc,或者office内网zone

挖坑,以后填。

其他的方案补充:

faq: