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安装tunctl用于新建TAP/TUN设备，TAP为以太网设备，TUN为网络层设备。

yum install tunctl
#debian下为uml-utilities

Client配置：

tunctl -t tap1
ifconfig tap4 192.168.1.1 netmask 255.255.255.0 up

Server配置：

tunctl -t tap2
ifconfig tap2 192.168.1.2 netmask 255.255.255.0 up
echo "PermitTunnel yes" >> /etc/ssh/sshd_config

Client发起SSH Tunnel连接：

ssh -N -f -o Tunnel=ethernet -w 1:2 remote-host
#-w local tap id:remote tap id

OpenWRT安装PPPoe服务器，当客户端连接或断开时通过ip-down.d/ip-up.d执行ROS命令，ROS需配置使用SSH Key验证。
当系统拨号断开时停止PPPoe：

mkdir /etc/ppp/ip-down.d
cat >/etc/ppp/ip-down.d/pppoe-down.sh << EOF
#!/bin/sh
ssh admin@192.168.1.21 "/interface pppoe-client disable pppoe-out1"
EOF
chmod +x /etc/ppp/ip-down.d/pppoe-down.sh 

当连接系统拨号连接时开启PPPoe：

mkdir /etc/ppp/ip-up.d
cat >/etc/ppp/ip-up.d/pppoe-up.sh << EOF
#!/bin/sh
ssh admin@192.168.1.21 "/interface pppoe-client enable pppoe-out1"
EOF
chmod +x /etc/ppp/ip-up.d/pppoe-up.sh 

2015.03.17更新：
ros重新拨号只需enable就行，无需先disable：

ssh admin@192.168.1.21 "/interface pppoe-client enable pppoe-out1"

OpenWRT更新到14.07安装的pppoe不执行ip-down.d或up目录下脚本，需添加相应脚本，PPPD连接时会执行此脚本：

cat >/etc/ppp/ip-up << EOF
#!/bin/sh
[ -d /etc/ppp/ip-up.d ] && {
        for SCRIPT in /etc/ppp/ip-up.d/*
        do
                [ -x "$SCRIPT" ] && "$SCRIPT" "$@"
        done
}
EOF
chmod +x /etc/ppp/ip-up

首先生成SSH key：

ssh-keygen -t dsa

复制SSH Key到ROS：

scp ~/.ssh/id_dsa.pub admin@192.168.1.21:

登录到ROS导入SSH Key：

user ssh-keys import public-key-file=id_dsa.pub user=admin 

然后就可免验证登录ROS了：

ssh admin@192.168.1.21

Xshell是Windows下功能强大的SSH管理软件，家庭及学生用户可免费使用，Xshell最近更新增加了官方中文版。
Xsehll最近更新：

Xshell 4 Build 0123, Feb 05, 2013

        FIX: Resource cleanup, minor bug fixes, feature update

Xshell 4 Build 0122, Jan 29, 2013

        ADD: French, German, Japanese, Spanish, Simplified Chinese, Traditional Chinese UI
        ADD: Use user defined string for keep alive
        FIX: Only the last tab can be reconnected when network goes down
        FIX: Transferring large data via serial crashes Xshell
        FIX: Local shell command is not displayed properly in some languages
        FIX: Problem transferring large files via Zmodem
        FIX: Tab name changes to COM1
        FIX: Incorrect selection area when double clicked to make selection then moved mouse to change selection area
        FIX: Some meta keys send incorrect value
        FIX: Resource cleanup, minor bug fixes, feature update

Xshell4官方中文版效果图：

一客户联系说VPS在让其朋友安装Squid后SSH不能登录了，分析OpenSSH未正常启动，然后通过VNC终端使用用户提供的密码也不能登录，当时以为密码有误，不得已进入单用户模式重置密码，然后再次尝试登录依旧，不得已再次进入单用户模式查找原因，验证错误日记如下：

Dec 27 14:36:30 ONOVPS login: pam_securetty(login:auth): /etc/securetty is either world writable or not a normal file
Dec 27 14:36:35 ONOVPS login: FAILED LOGIN 1 FROM (null) FOR root, Authentication failure

可见是/etc/securetty文件或权限有问题，此文件可限制root登录的终端，正常权限600，查看权限：

ls -al /etc/securetty 
-rwxrwxrwx 1 root root 127 Mar  3  2011 /etc/securetty

重置权限正常登入VPS，启动SSH依旧提示权限有误，查看/etc/目录竟然都整成777权限了，那个郁闷呀。。。。