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    六步搞定centos 6下l2tp + ipsec VPN服务器配置

    centos admin 6494浏览 0评论

    近年来最累的一次折腾。有必要好好记录一下。跟了网上N个教程，有好几个都走不通。最后自己彻底整理了一次。把自己的经验和配置分享出来。

    首先隆重感谢一下至今素未谋面的老熊，真是好人啊。06年的时候就在plesk服务器换ip的事上，帮了我好大的忙。没想到这次在我卡在第6步，最绝望的时候，这只熊的婀娜身影再一次出现在了我的生活中。还在漆黑的深夜中陪伴在我的身边。以下隆重公布一下他的QQ，造福广大网友！QQ: 499******* （后几位号码，为符合当地莫名其妙的“相关法规”，被系统自动屏蔽。。。）

    其次要感谢老熊的同事，百忙中写好的防火墙规则，让我10分钟之内，就被兴奋得昏了头的我，给无情覆盖了。以至于下次人家重写之后，很自觉的在/root下给留了个备份。zan


    1. 先安装openswan

    yum install -y ppp iptables make gcc gmp-devel xmlto bison flex xmlto libpcap-devel lsof
    wget http://download.openswan.org/openswan/openswan-2.6.38.tar.gz
    tar zxvf openswan-2.6.38.tar.gz
    cd openswan-2.6.38
    make programs install



    gkp说“安装 openswan，记得别用2.6.26，宁可用2.6.24。他和xl2tpd存在严重兼容性bug”


    2. 安装xl2tpd

    在centos 6官方的yum源中，没有这个软件包。需要安装fedora的epel源。

    rpm -Uvh http://mirrors.ustc.edu.cn/fedora/epel/6/x86_64/epel-release-6-7.noarch.rpm
    #CentOS 5用这个地址：  rpm -Uvh http://mirrors.ustc.edu.cn/fedora/epel/5/i386/epel-release-5-4.noarch.rpm
    yum install xl2tpd -y



    如果上面这个安装地址如果不对了。参照这个fedora epel的faq页（https://fedoraproject.org/wiki/EPEL/FAQ/zh-cn#How_can_I_install_the_packages_from_the_EPEL_software_repository.3F）

    安装其他一些linux软件源，参照这页：http://www.esojourn.org/blog/post/repo-sources.php


    编辑 /etc/ipsec.conf 注意$esojourn.org替换成你机器的ip。这个IP应该是你的公网IP，不是本机内网IP。

    # /etc/ipsec.conf – Openswan IPsec configuration file

    # This file:  /usr/local/share/doc/openswan/ipsec.conf-sample
    #
    # Manual:     ipsec.conf.5

    version 2.0     # conforms to second version of ipsec.conf specification

    # basic configuration
    config setup
    # Do not set debug options to debug configuration issues!
    # plutodebug / klipsdebug = “all”, “none” or a combation from below:
    # “raw crypt parsing emitting control klips pfkey natt x509 dpd private”
    # eg:
    # plutodebug=”control parsing”
    # Again: only enable plutodebug or klipsdebug when asked by a developer
    #
    # enable to get logs per-peer
    # plutoopts=”–perpeerlog”
    #

    # Enable core dumps (might require system changes, like ulimit -C)
    # This is required for abrtd to work properly
    # Note: incorrect SElinux policies might prevent pluto writing the core
    dumpdir=/var/run/pluto/
    #
    # NAT-TRAVERSAL support, see README.NAT-Traversal
    nat_traversal=yes
    # exclude networks used on server side by adding %v4:!a.b.c.0/24
    # It seems that T-Mobile in the US and Rogers/Fido in Canada are
    # using 25/8 as “private” address space on their 3G network.
    # This range has not been announced via BGP (at least upto 2010-12-21)
    virtual_private=%v4:10.0.0.0/8,%v4:192.168.0.0/16,%v4:172.16.0.0/12,%v4:25.0.0.0/8,%v6:fd00::/8,%v6:fe80::/10
    # OE is now off by default. Uncomment and change to on, to enable.
    oe=off
    # which IPsec stack to use. auto will try netkey, then klips then mast

    protostack=netkey
    #这里注释说可以用auto，但实际上不行。还得老老实实写netkey

    # Use this to log to a file, or disable logging on embedded systems (like openwrt)
    #plutostderrlog=/dev/null

    # Add connections here

    # sample VPN connection
    # for more examples, see /etc/ipsec.d/examples/
    #conn sample
    #               # Left security gateway, subnet behind it, nexthop toward right.
    #               left=10.0.0.1
    #               leftsubnet=172.16.0.0/24
    #               leftnexthop=10.22.33.44
    #               # Right security gateway, subnet behind it, nexthop toward left.
    #               right=10.12.12.1
    #               rightsubnet=192.168.0.0/24
    #               rightnexthop=10.101.102.103
    #               # To authorize this connection, but not actually start it,
    #               # at startup, uncomment this.
    #               #auto=add

    conn L2TP-PSK-NAT
    rightsubnet=vhost:%priv
    also=L2TP-PSK-noNAT

    conn L2TP-PSK-noNAT
    authby=secret
    pfs=no
    auto=add
    keyingtries=3
    rekey=no
    ikelifetime=8h
    keylife=1h
    type=transport
    left=$esojourn.org  #这里写公网IP，没固定IP的就到花生壳弄个动态域名解析。
    leftid=$esojourn.org
    leftprotoport=17/1701
    right=%any


    修改ipsec密钥

    vi  /etc/ipsec.secrets

    www.esojourn.org %any: PSK “myps”
    #www.esojourn.org改成公网ip，没固定IP的，就到花生壳弄个动态域名解析。http://www.oray.com/peanuthull/
    #myps改成密码



    3. 修改/etc/sysctl.conf，开启路由功能

    vi /etc/sysctl.conf


    星云说：
    将下面两项找到：

    net.ipv4.ip_forward = 0
    net.ipv4.conf.default.rp_filter = 1


    改为：

    net.ipv4.ip_forward = 1
    net.ipv4.conf.default.rp_filter = 0


    之后先让修改后的配置生效，再测试一下，

    sysctl -p
    service ipsec start
    ipsec verify



    如果行了就这样了，但实际上，我反复测试之后，干脆在sysctl.conf最下面，加了这一段。加好后别忘了再sysctl -p一下。

    #added for xl2tpd
    net.ipv4.ip_forward = 1
    net.ipv4.conf.default.rp_filter = 0
    net.ipv4.conf.all.send_redirects = 0
    net.ipv4.conf.default.send_redirects = 0
    net.ipv4.conf.all.log_martians = 0
    net.ipv4.conf.default.log_martians = 0
    net.ipv4.conf.default.accept_source_route = 0
    net.ipv4.conf.all.accept_redirects = 0
    net.ipv4.conf.default.accept_redirects = 0
    net.ipv4.icmp_ignore_bogus_error_responses = 1



    如果ipsec verify返回这样，就可以了。

    Checking your system to see if IPsec got installed and started correctly:
    Version check and ipsec on-path                                 [OK]
    Linux Openswan U2.6.24/K2.6.32.16-linode28 (netkey)
    Checking for IPsec support in kernel                            [OK]
    NETKEY detected, testing for disabled ICMP send_redirects       [OK]
    NETKEY detected, testing for disabled ICMP accept_redirects     [OK]
    Checking for RSA private key (/etc/ipsec.secrets)               [OK]
    Checking that pluto is running                                  [OK]
    Pluto listening for IKE on udp 500                              [OK]
    Pluto listening for NAT-T on udp 4500                           [OK]
    Two or more interfaces found, checking IP forwarding            [OK]
    Checking NAT and MASQUERADEing
    Checking for ‘ip’ command                                       [OK]
    Checking for ‘iptables’ command                                 [OK]
    Opportunistic Encryption Support                                [DISABLED]



    我的经验中，这里可能会出这么几个故障：
    第一：

    SAref kernel support                                           [N/A]


    这样的话， /etc/xl2tpd/xl2tpd.conf这个文件里

    [global]
    ipsec saref = no



    第二：

    Two or more interfaces found, checking IP forwarding            [FAILED]
    Checking NAT and MASQUERADEing                                  [OK]

    ip转发检查失败。

    Paul和Steve说：只要 cat /proc/sys/net/ipv4/ip_forward 返回结果是1就没事。这个我已经证实了。

    第三：返回结果里，就没有Two or more interfaces found, checking IP forwarding和Checking NAT and MASQUERADEing这两项。碰上这个我也没办法了。重装了系统，又瞎折腾一通之后就好了。

    [ 2012-7-6 ]
    第四：更新加入一个新的情况

    Checking for IPsec support in kernel                            [OK]
    SAref kernel support                                           [N/A]
    NETKEY:  Testing XFRM related proc values                      [OK]
    [OK]
    [FAILED]

    Please enable /proc/sys/net/core/xfrm_larval_drop
    or NETKEY will cause non-POSIX compliant long time-outs

    Checking that pluto is running                                  [OK]


    出这毛病，照着说明，

    echo 1 > /proc/sys/net/core/xfrm_larval_drop
    vi /etc/bashrc


    然后把“echo 1 > /proc/sys/net/core/xfrm_larval_drop”这句加进去。以后每次开机自动执行一下。

    4. 编辑 /etc/xl2tpd/xl2tpd.conf
    vi /etc/xl2tpd/xl2tpd.conf

    ; This is a minimal sample xl2tpd configuration file for use
    ; with L2TP over IPsec.
    ;
    ; The idea is to provide an L2TP daemon to which remote Windows L2TP/IPsec
    ; clients connect. In this example, the internal (protected) network
    ; is 192.168.1.0/24.  A special IP range within this network is reserved
    ; for the remote clients: 192.168.1.128/25
    ; (i.e. 192.168.1.128 … 192.168.1.254)
    ;
    ; The listen-addr parameter can be used if you want to bind the L2TP daemon
    ; to a specific IP address instead of to all interfaces. For instance,
    ; you could bind it to the interface of the internal LAN (e.g. 192.168.1.98
    ; in the example below). Yet another IP address (local ip, e.g. 192.168.1.99)
    ; will be used by xl2tpd as its address on pppX interfaces.

    [global]
    listen-addr = esojourn.org
    ;这里写内网IP。或者加;注释掉也问题不大。
    ;
    ; requires openswan-2.5.18 or higher – Also does not yet work in combination
    ; with kernel mode l2tp as present in linux 2.6.23+
    ; ipsec saref = yes
    ipsec saref = no
    ;这里一般都让写yes，但如果刚才你的ipsec verify中，有报SAref kernel support[N/A]的话，这里就写no。

    ; Use refinfo of 22 if using an SAref kernel patch based on openswan 2.6.35 or
    ;  when using any of the SAref kernel patches for kernels up to 2.6.35.
    ; ipsec refinfo = 30
    ;
    ; forceuserspace = yes
    ;
    ; debug tunnel = yes

    [lns default]
    ip range = 192.168.7.128-192.168.7.254
    ;这里写vpn client的ip段
    local ip = 192.168.7.1

    require chap = yes
    refuse pap = yes
    require authentication = yes
    name = LinuxVPNserver
    ppp debug = yes
    pppoptfile = /etc/ppp/options.xl2tpd
    length bit = yes



    5. 修改 /etc/ppp/options.xl2tpd

    vi /etc/ppp/options.xl2tpd

    require-mschap-v2
    ipcp-accept-local
    ipcp-accept-remote
    ms-dns  8.8.4.4
    ms-dns  8.8.8.8
    noccp
    auth
    crtscts
    idle 1800
    mtu 1410
    mru 1410
    nodefaultroute
    debug
    lock
    proxyarp
    connect-delay 5000



    vi /etc/ppp/chap-secrets

    #文件格式
    # user server password ip
    username * userpass * #改成你的用户名 密码



    6. 最关键的iptables配置
    做完上面这堆步骤之后，客户端建个连接就可以验证进入vpn主机了。但是无法访问内外网。我就是在这里卡了一个多星期。网上的资料，有的没说这一步。有的说了也没说全。我发个权威的吧。

    iptables -t nat -A POSTROUTING -s 192.168.7.0/24 -o eth0 -j MASQUERADE
    iptables -I FORWARD -s 192.168.7.0/24 -j ACCEPT
    iptables -I FORWARD -d 192.168.7.0/24 -j ACCEPT
    iptables-save
    service iptables restart


    192.168.7.0/24根据实际情况替换。

    vi /etc/sysconfig/iptables 看到的应该是类似这样。
    最上面先是nat规则，下面是filter规则。
    下面filter表里，先把VPN要用到的udp端口1701，500，4500都打开。要用openvp的话，还要开1194。
    另外filter表里，一定要有FORWARD规则。这点在网上好几个教程里都没说！坑死人。

    #下面规则做参考啊，新手别完全照抄。
    *nat
    :PREROUTING ACCEPT [39:3503]
    :POSTROUTING ACCEPT [0:0]
    :OUTPUT ACCEPT [0:0]
    -A POSTROUTING -s 192.168.7.0/24 -o eth0 -j MASQUERADE
    COMMIT
    # Completed on Thu Jun 28 15:50:40 2012
    # Generated by iptables-save v1.4.7 on Thu Jun 28 15:50:40 2012
    *filter
    :INPUT ACCEPT [0:0]
    :FORWARD ACCEPT [0:0]
    :OUTPUT ACCEPT [121:13264]
    -A INPUT -m state –state RELATED,ESTABLISHED -j ACCEPT
    -A INPUT -p icmp -j ACCEPT
    -A INPUT -i lo -j ACCEPT
    -A INPUT -p tcp -m state –state NEW -m tcp –dport 22 -j ACCEPT
    -A INPUT -p tcp -m state –state NEW -m tcp –dport 80 -j ACCEPT
    -A INPUT -p tcp -m state –state NEW -m tcp –dport 53 -j ACCEPT
    -A INPUT -p udp -m state –state NEW -m udp –dport 53 -j ACCEPT
    -A INPUT -p tcp -m state –state NEW -m tcp –dport 1194 -j ACCEPT
    -A INPUT -p udp -m state –state NEW -m udp –dport 1701 -j ACCEPT
    -A INPUT -p udp -m state –state NEW -m udp –dport 500 -j ACCEPT
    -A INPUT -p udp -m state –state NEW -m udp –dport 4500 -j ACCEPT

    -A INPUT -j REJECT –reject-with icmp-host-prohibited
    -A FORWARD -d 192.168.7.0/24 -j ACCEPT
    -A FORWARD -s 192.168.7.0/24 -j ACCEPT
    -A FORWARD -j REJECT –reject-with icmp-host-prohibited
    COMMIT
    # Completed on Thu Jun 28 15:50:40 2012



    最后

    service xl2tpd restart
    service iptables restart
    chkconfig xl2tpd on
    chkconfig iptables on
    chkconfig ipsec on

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