前言
以前连接回公司，经常都是使用 OpenVPN、PPTP、L2TP 什么的，感觉不是很难用，但也说不上很好用。但是因为大家都知道的原因，在 iOS 上 OpenVPN 基本上无法正常下载，这对于公司员工来说就比较麻烦了，因为并不是每个人都需要科学上网的。后来无意中发现了 OpenConnect VPN Server，感觉还不错，后来就用到公司网络上了。使用过一段时间，就考虑把家里的 OpenWrt 也装一个，这样外出的时候连回家里管理 NAS 也方便些，便有了此文。
前期准备
- 首先，你得有个刷了 OpenWrt 的路由器，版本Chaos Calmer 15.05
- 自己配置好 DDNS 等服务器。
- （可选）花钱或者免费弄一个服务器 SSL/TLS 证书
开工
安装 ocserv 和 ddns
我是命令行粉丝，所以大部分工作在 Terminal 下完成。
opkg update opkg install luci-app-ocserv opkg install luci-app-ddns
装好后的效果如下：安装 Web 界面的ocserv和ddns，其实装ddns并不是为了真正的动态域名，而是ocserv的脚本会检测系统中是否有ddns，如果有的话，ocserv的配置脚本会自动把动态域名设置为true，如果喜欢自己改脚本的，也可以不装ddns，这样可以解决点空间。
修改配置文件
安装好后，系统会自动生成以下 7 个文件：
/etc/ocserv/ca.pem /etc/ocserv/ca-key.pem /etc/ocserv/server-cert.pem /etc/ocserv/server-key.pem /etc/ocserv/ocserv.conf.template /etc/ocserv/pki/ca.tmpl /etc/ocserv/pki/server.tmpl
一般来说 CA 相关的可以不用管，如果你找了如 StartSSL 签了免费的证书的话，用他们签名过的公私钥替换server-cert.pem和server-key.pem就好了。其中ca.pem是服务器的 CA 证书，ca-key.pem是私钥，server-cert.pem是服务器证书，server-key.pem是服务器私钥。
接下来修改模板文件ocserv.conf.template，这个可以在命令行中用 Vim 操作，也可以在 Web 界面来操作，比如：
以下为使用「证书」方式来进行身份验证的，所以直接忽略系统默认的plain认证方式，如果使用该方式可以参考文章最后的参考文献。最终的配置文件如下：
# User authentication method. Could be set multiple times and in that case
# all should succeed.
# Options: certificate, pam.
auth = "certificate"
#auth = "pam"
# The gid-min option is used by auto-select-group option, in order to
# select the minimum group ID.
#auth = "pam[gid-min=1000]"
# The plain option requires specifying a password file which contains
# entries of the following format.
# "username:groupname:encoded-password"
# One entry must be listed per line, and 'ocpasswd' can be used
# to generate password entries.
#auth = "|AUTH|"
# A banner to be displayed on clients
#banner = "Welcome to OpenWRT"
#isolate-workers = true
# When the server has a dynamic DNS address (that may change),
# should set that to true to ask the client to resolve again on
# reconnects.
listen-host-is-dyndns = |DYNDNS|
# Use listen-host to limit to specific IPs or to the IPs of a provided
# hostname.
#listen-host = [IP|HOSTNAME]
# Limit the number of clients. Unset or set to zero for unlimited.
#max-clients = 1024
max-clients = |MAX_CLIENTS|
# Limit the number of client connections to one every X milliseconds
# (X is the provided value). Set to zero for no limit.
rate-limit-ms = 100
# Limit the number of identical clients (i.e., users connecting
# multiple times). Unset or set to zero for unlimited.
max-same-clients = |MAX_SAME|
# TCP and UDP port number
tcp-port = |PORT|
|UDP|udp-port = |PORT|
# Stats report time. The number of seconds after which each
# worker process will report its usage statistics (number of
# bytes transferred etc). This is useful when accounting like
# radius is in use.
#stats-report-time = 360
# Keepalive in seconds
keepalive = 32400
# Dead peer detection in seconds.
dpd = |DPD|
# Dead peer detection for mobile clients. The needs to
# be much higher to prevent such clients being awaken too
# often by the DPD messages, and save battery.
# (clients that send the X-AnyConnect-Identifier-DeviceType)
#mobile-dpd = 1800
# MTU discovery (DPD must be enabled)
try-mtu-discovery = false
# The key and the certificates of the server
# The key may be a file, or any URL supported by GnuTLS (e.g.,
# tpmkey:uuid=xxxxxxx-xxxx-xxxx-xxxx-xxxxxxxx;storage=user
# or pkcs11:object=my-vpn-key;object-type=private)
#
# There may be multiple certificate and key pairs and each key
# should correspond to the preceding certificate.
server-cert = /etc/ocserv/server-cert.pem
server-key = /etc/ocserv/server-key.pem
# Diffie-Hellman parameters. Only needed if you require support
# for the DHE ciphersuites (by default this server supports ECDHE).
# Can be generated using:
# certtool --generate-dh-params --outfile /path/to/dh.pem
#dh-params = /path/to/dh.pem
# If you have a certificate from a CA that provides an OCSP
# service you may provide a fresh OCSP status response within
# the TLS handshake. That will prevent the client from connecting
# independently on the OCSP server.
# You can update this response periodically using:
# ocsptool --ask --load-cert=your_cert --load-issuer=your_ca --outfile response
# Make sure that you replace the following file in an atomic way.
#ocsp-response = /path/to/ocsp.der
# In case PKCS #11 or TPM keys are used the PINs should be available
# in files. The srk-pin-file is applicable to TPM keys only, and is the
# storage root key.
#pin-file = /path/to/pin.txt
#srk-pin-file = /path/to/srkpin.txt
# The Certificate Authority that will be used to verify
# client certificates (public keys) if certificate authentication
# is set.
ca-cert = /etc/ocserv/ca.pem
# The object identifier that will be used to read the user ID in the client
# certificate. The object identifier should be part of the certificate's DN
# Useful OIDs are:
# CN = 2.5.4.3, UID = 0.9.2342.19200300.100.1.1
cert-user-oid = 2.5.4.3
# The object identifier that will be used to read the user group in the
# client certificate. The object identifier should be part of the certificate's
# DN. Useful OIDs are:
# OU (organizational unit) = 2.5.4.11
#cert-group-oid = 2.5.4.11
# The revocation list of the certificates issued by the 'ca-cert' above.
#crl = /etc/ocserv/crl.pem
# Uncomment this to enable compression negotiation (LZS, LZ4).
|COMPRESSION|compression = true
# GnuTLS priority string
tls-priorities = "NORMAL:%SERVER_PRECEDENCE:%COMPAT:-VERS-SSL3.0"
# To enforce perfect forward secrecy (PFS) on the main channel.
#tls-priorities = "NORMAL:%SERVER_PRECEDENCE:%COMPAT:-VERS-SSL3.0:-RSA"
# The time (in seconds) that a client is allowed to stay connected prior
# to authentication
auth-timeout = 40
# The time (in seconds) that a client is allowed to stay idle (no traffic)
# before being disconnected. Unset to disable.
#idle-timeout = 1200
# The time (in seconds) that a mobile client is allowed to stay idle (no
# traffic) before being disconnected. Unset to disable.
#mobile-idle-timeout = 2400
# The time (in seconds) that a client is not allowed to reconnect after
# a failed authentication attempt.
min-reauth-time = 360
# Banning clients in ocserv works with a point system. IP addresses
# that get a score over that configured number are banned for
# min-reauth-time seconds. By default a wrong password attempt is 10 points,
# a KKDCP POST is 1 point, and a connection is 1 point. Note that
# due to difference processes being involved the count of points
# will not be real-time precise.
#
# Score banning cannot be reliably used when receiving proxied connections
# locally from an HTTP server (i.e., when listen-clear-file is used).
#
# Set to zero to disable.
max-ban-score = 50
# The time (in seconds) that all score kept for a client is reset.
ban-reset-time = 300
# In case you'd like to change the default points.
#ban-points-wrong-password = 10
#ban-points-connection = 1
#ban-points-kkdcp = 1
# Cookie timeout (in seconds)
# which he can reconnect. That cookie will be invalided if not
# used within this timeout value. On a user disconnection, that
# cookie will also be active for this time amount prior to be
# invalid. That should allow a reasonable amount of time for roaming
# between different networks.
cookie-timeout = 300
# Whether roaming is allowed, i.e., if true a cookie is
# restricted to a single IP address and cannot be re-used
# from a different IP.
deny-roaming = false
# ReKey time (in seconds)
# ocserv will ask the client to refresh keys periodically once
# this amount of seconds is elapsed. Set to zero to disable.
rekey-time = 172800
# ReKey method
# Valid options: ssl, new-tunnel
# ssl: Will perform an efficient rehandshake on the channel allowing
# a seamless connection during rekey.
# new-tunnel: Will instruct the client to discard and re-establish the channel.
# Use this option only if the connecting clients have issues with the ssl
# option.
rekey-method = ssl
# Script to call when a client connects and obtains an IP
# Parameters are passed on the environment.
# REASON, USERNAME, GROUPNAME, HOSTNAME (the hostname selected by client),
# DEVICE, IP_REAL (the real IP of the client), IP_LOCAL (the local IP
# in the P-t-P connection), IP_REMOTE (the VPN IP of the client),
# ID (a unique numeric ID); REASON may be "connect" or "disconnect".
# These scripts are not needed if you have setup an interface for all vpns+
# devices.
#connect-script = /usr/bin/ocserv-script
#disconnect-script = /usr/bin/ocserv-script
# UTMP
use-utmp = false
# Whether to enable support for the occtl tool (i.e., either through D-BUS,
# or via a unix socket).
use-occtl = true
# socket file used for IPC with occtl. You only need to set that,
# if you use more than a single servers.
occtl-socket-file = /var/run/occtl.socket
# PID file. It can be overriden in the command line.
pid-file = /var/run/ocserv.pid
# The default server directory. Does not require any devices present.
chroot-dir = /var/lib/ocserv
# socket file used for IPC, will be appended with .PID
# It must be accessible within the chroot environment (if any)
#socket-file = /var/run/ocserv-socket
socket-file = ocserv-socket
# The user the worker processes will be run as. It should be
# unique (no other services run as this user).
run-as-user = ocserv
run-as-group = ocserv
# Set the protocol-defined priority (SO_PRIORITY) for packets to
# be sent. That is a number from 0 to 6 with 0 being the lowest
# priority. Alternatively this can be used to set the IP Type-
# Of-Service, by setting it to a hexadecimal number (e.g., 0x20).
# This can be set per user/group or globally.
#net-priority = 3
# Set the VPN worker process into a specific cgroup. This is Linux
# specific and can be set per user/group or globally.
#cgroup = "cpuset,cpu:test"
#
# Network settings
#
# The name of the tun device
device = vpns
# Whether the generated IPs will be predictable, i.e., IP stays the
# same for the same user when possible.
predictable-ips = |PREDICTABLE_IPS|
# The default domain to be advertised
|ENABLE_DEFAULT_DOMAIN|default-domain = |DEFAULT_DOMAIN|
# The pool of addresses that leases will be given from.
ipv4-network = |IPV4ADDR|
ipv4-netmask = |NETMASK|
# The advertized DNS server. Use multiple lines for
# multiple servers.
# dns = fc00::4be0
#dns = 192.168.1.2
# The NBNS server (if any)
#nbns = 192.168.1.3
# The IPv6 subnet that leases will be given from.
|ENABLE_IPV6|ipv6-network = |IPV6ADDR|
|ENABLE_IPV6|ipv6-prefix = |IPV6PREFIX|
# The domains over which the provided DNS should be used. Use
# multiple lines for multiple domains.
#split-dns = example.com
# Prior to leasing any IP from the pool ping it to verify that
# it is not in use by another (unrelated to this server) host.
ping-leases = false
# Unset to assign the default MTU of the device
# mtu =
# Unset to enable bandwidth restrictions (in bytes/sec). The
# setting here is global, but can also be set per user or per group.
#rx-data-per-sec = 40000
#tx-data-per-sec = 40000
# The number of packets (of MTU size) that are available in
# the output buffer. The default is low to improve latency.
# Setting it higher will improve throughput.
#output-buffer = 10
# Routes to be forwarded to the client. If you need the
# client to forward routes to the server, you may use the
# config-per-user/group or even connect and disconnect scripts.
#
# To set the server as the default gateway for the client just
# comment out all routes from the server.
#route = 192.168.1.0/255.255.255.0
#route = 192.168.5.0/255.255.255.0
#route = fef4:db8:1000:1001::/64
# Configuration files that will be applied per user connection or
# per group. Each file name on these directories must match the username
# or the groupname.
# The options allowed in the configuration files are dns, nbns,
# ipv?-network, ipv4-netmask, ipv6-prefix, rx/tx-per-sec, iroute, route,
# net-priority and cgroup.
#
# Note that the 'iroute' option allows to add routes on the server
# based on a user or group. The syntax depends on the input accepted
# by the commands route-add-cmd and route-del-cmd (see below).
config-per-user = /etc/ocserv/config-per-user/
config-per-group = /etc/ocserv/config-per-group/
# When config-per-xxx is specified and there is no group or user that
# matches, then utilize the following configuration.
#default-user-config = /etc/ocserv/defaults/user.conf
#default-group-config = /etc/ocserv/defaults/group.conf
# Groups that a client is allowed to select from.
# A client may belong in multiple groups, and in certain use-cases
# it is needed to switch between them. For these cases the client can
# select prior to authentication. Add multiple entries for multiple groups.
#select-group = group1
#select-group = group2[My group 2]
#select-group = tost[The tost group]
# The name of the group that if selected it would allow to use
# the assigned by default group.
#default-select-group = DEFAULT
# Instead of specifying manually all the allowed groups, you may instruct
# ocserv to scan all available groups and include the full list. That
# option is only functional on plain authentication.
#auto-select-group = true
# The system command to use to setup a route. %{R} will be replaced with the
# route/mask and %{D} with the (tun) device.
#
# The following example is from linux systems. %{R} should be something
# like 192.168.2.0/24
route-add-cmd = "/sbin/route add -net %{R} dev %{D}"
route-del-cmd = "/sbin/route del -net %{R} dev %{D}"
# This option allows to forward a proxy. The special strings '%{U}'
# and '%{G}', if present will be replaced by the username and group name.
#proxy-url = http://example.com/
#proxy-url = http://example.com/%{U}/%{G}/hello
#
# The following options are for (experimental) AnyConnect client
# compatibility.
# Client profile xml. A sample file exists in doc/profile.xml.
# This file must be accessible from inside the worker's chroot.
# It is not used by the openconnect client.
#user-profile = profile.xml
# Binary files that may be downloaded by the CISCO client. Must
# be within any chroot environment.
#binary-files = /path/to/binaries
# Unless set to false it is required for clients to present their
# certificate even if they are authenticating via a previously granted
# cookie and complete their authentication in the same TCP connection.
# Legacy CISCO clients do not do that, and thus this option should be
# set for them.
cisco-client-compat = |CISCO_COMPAT|
#Advanced options
# Option to allow sending arbitrary custom headers to the client after
# authentication and prior to VPN tunnel establishment.
#custom-header = "X-My-Header: hi there"
主要的改动点：
- 认证方式修改为 certificate
- 禁用 banner
- 打开 ca-cert
- 将 cert-user-oid 修改为 CN (2.5.4.3) 识别
当ocserv服务启动的时候，会自动生成/var/etc/ocserv.conf文件作为最终的配置文件。
设置路由表、转发规则和端口映射
修改完配置文件以后，我们还需要设置路由表。因为我不需要 OpenWrt 代理所有流量，仅仅需要可以访问到内网，所以我只做了一个路由表，就是我的内网网段，如下图：
接下来添加自定义防火墙，或修改 firewall 文件/etc/firewall.user，增加如下内容：
iptables -A input_rule -i vpns+ -j ACCEPT iptables -A forwarding_rule -i vpns+ -j ACCEPT iptables -A forwarding_rule -o vpns+ -j ACCEPT iptables -A output_rule -o vpns+ -j ACCEPT
添加防火墙规则后重启服务。
最后 在防火墙-添加通信规则，ocserv安装后默认使用4443端口，如图：
启动 ocserv 服务
/etc/init.d/ocserv enable /etc/init.d/ocserv start
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这个命令很简单，另外，也可以在 luci 中选择Enable server来打开ocserv服务。然而，在你重启后，ocserv服务从来就没有自动启动过！！！所以，我们还得做些 tweaking。
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在/etc/rc.local文件的exit前面增加两行：
/etc/init.d/ocserv restart sleep 5
同时创建一个/root/ocservup.sh脚本，防止ocserv进程意外被杀：
#!/bin/sh killall -0 ocserv 2> /dev/null if [ $? != 0 ] then logger \"$0: Starting ocserv ...\" /usr/sbin/ocserv -c /var/etc/ocserv.conf else logger \"$0: ocserv already running: $(pidof ocserv)\" fi
记得执行chmod +x /root/ocservup.sh给该脚本添加可执行属性。然后把该脚本添加到crontab中：
3 */2 * * * /root/ocservup.sh
至此，整个配置完成，可以重启试试。
参考文献
