服务管理——telnet

矫情吗；* 2022-10-30 05:28 130阅读 0赞

## 一 telnet服务端和客户端 ##

什么是Telnet？

Telnet协议是TCP/IP协议族中的一员，是Internet远程登陆服务的标准协议和主要方式。它为用户提供了在本地计算机上完成远程主机工作的能力。在终端使用者的电脑上使用telnet程序，用它连接到服务器。终端使用者可以在telnet程序中输入命令，这些命令会在服务器上运行，就像直接在服务器的控制台上输入一样。可以在本地就能控制服务器。要开始一个telnet会话，必须输入用户名和密码来登录服务器。Telnet是常用的远程控制Web服务器的方法。

#Server01：安装telnet服务端
    [root@serv01 xinetd.d]# yum installtelnet-server* -y
    #开启服务
    [root@serv01 xinetd.d]# chkconfig telnet on
    #重启xinetd服务
    [root@serv01 xinetd.d]# /etc/init.d/xinetdrestart
    Stopping xinetd:                                          [  OK  ]
    Starting xinetd:                                          [  OK  ]
    #再次查看网络状态
    [root@serv01 xinetd.d]# netstat -langput |grep "telnet"
    tcp       0      0 192.168.1.11:23             192.168.1.12:57169          ESTABLISHED 2488/in.telnetd: 19
    [root@serv01 xinetd.d]# netstat -langput |grep "xin"
    tcp       0      0 :::22                       :::*                        LISTEN      2486/xinetd        
    tcp       0      0 :::23                       :::*                        LISTEN      2486/xinetd   
          
    #Server02：安装telnet客户端
    [root@serv02 .ssh]# yum install telnet -y
    #客户端通过telnet远程连接登录，注意一定要使用普通用户
    [root@serv02 .ssh]# telnet 192.168.1.11
    Trying 192.168.1.11...
    Connected to 192.168.1.11.
    Escape character is '^]'.
    Red Hat Enterprise Linux Server release 6.1(Santiago)
    Kernel 2.6.32-131.0.15.el6.x86_64 on anx86_64
    login: hongyi
    Password:
    Last login: Tue Aug  6 19:44:31 from 192.168.1.1
    [hongyi@serv01 ~]$

## 二 telnet的特性 ##

#明文传输，不允许root登录
    #telnet是明文传输，不允许root登录
    #我们往往使用普通用户登录，然后su -切换到root用户。
    [root@serv02 .ssh]# telnet 192.168.1.11
    Trying 192.168.1.11...
    Connected to 192.168.1.11.
    Escape character is '^]'.
    Red Hat Enterprise Linux Server release 6.1(Santiago)
    Kernel 2.6.32-131.0.15.el6.x86_64 on anx86_64
    login: root
    Password:
    Login incorrect
     
    [root@serv01 xinetd.d]# pwd
    /etc/xinetd.d
    [root@serv01 xinetd.d]# cat telnet
    # default: on
    # description: The telnet server servestelnet sessions; it uses \
    #     unencryptedusername/password pairs for authentication.
    service telnet
    {
           disable   = no
           flags             = REUSE
           socket_type  = stream       
           wait              = no
           user              = root
           server           = /usr/sbin/in.telnetd
           log_on_failure    += USERID
    }
          
    #service ssh：名字必须唯一，不要重复

## 三 telnet只允许某个IP或者某个网段访问（only\_from） ##

#编辑文件，只允许192.168.1.12访问
    [root@serv01 xinetd.d]# vim telnet
    [root@serv01 xinetd.d]# cat telnet
    # default: on
    # description: The telnet server servestelnet sessions; it uses \
    #     unencryptedusername/password pairs for authentication.
    service telnet
    {
           disable   = no
           flags             = REUSE
           socket_type  = stream       
           wait              = no
           user              = root
           server           = /usr/sbin/in.telnetd
           log_on_failure    += USERID
           only_from    = 192.168.1.12
    }
    #重启服务
    [root@serv01 xinetd.d]# /etc/init.d/xinetd restart
    Stopping xinetd:                                          [  OK  ]
    Starting xinetd:                                          [  OK  ]
     
    #serv02可以正常访问
    [root@serv02 .ssh]# telnet 192.168.1.11
    Trying 192.168.1.11...
    Connected to 192.168.1.11.
    Escape character is '^]'.
    Red Hat Enterprise Linux Server release 6.1(Santiago)
    Kernel 2.6.32-131.0.15.el6.x86_64 on anx86_64
    login: hongyi
    Password:
    Last login: Tue Aug  6 23:20:57 from 192.168.1.12
    [hongyi@serv01 ~]$ exit
    ogout
    Connection closed by foreign host.
    [root@serv02 .ssh]#
     
    #serv02不可以正常访问
    [root@serv03 .ssh]# yum install telnet -y
    [root@serv03 .ssh]# telnet 192.168.1.11
    Trying 192.168.1.11...
    Connected to 192.168.1.11.
    Escape character is '^]'.
    Connection closed by foreign host.
     
     
    192.168.1.0/24 172.16.1.0/24
    192.168.1.0/255.255.255.0 X
     
    access_times = 8:30-17:00

## 四 telnet不允许某个IP或者某个网段访问（no\_access） ##

#no_access
    [root@serv01 xinetd.d]# vim telnet
    [root@serv01 xinetd.d]# cat telnet
    # default: on
    # description: The telnet server servestelnet sessions; it uses \
    #     unencryptedusername/password pairs for authentication.
    service telnet
    {
           disable   = no
           flags             = REUSE
           socket_type  = stream       
           wait              = no
           user              = root
           server           = /usr/sbin/in.telnetd
           log_on_failure    += USERID
           no_access     = 192.168.1.12
    }
    [root@serv01 xinetd.d]# /etc/init.d/xinetdrestart
    Stopping xinetd:                                          [  OK  ]
    Starting xinetd:                                          [  OK  ]
     
    [root@serv02 .ssh]# telnet 192.168.1.11
    Trying 192.168.1.11...
    Connected to 192.168.1.11.
    Escape character is '^]'.
    Connection closed by foreign host.
     
    [root@serv03 .ssh]# telnet 192.168.1.11
    Trying 192.168.1.11...
    Connected to 192.168.1.11.
    Escape character is '^]'.
    Red Hat Enterprise Linux Server release 6.1(Santiago)
    Kernel 2.6.32-131.0.15.el6.x86_64 on anx86_64
    login: hongyi
    Password:
    Last login: Tue Aug  6 23:41:22 from 192.168.1.12
    [hongyi@serv01 ~]$
     
    #网段
     
    [root@serv01 xinetd.d]# vim telnet
    [root@serv01 xinetd.d]# cat telnet
    # default: on
    # description: The telnet server servestelnet sessions; it uses \
    #     unencryptedusername/password pairs for authentication.
    service telnet
    {
           disable   = no
           flags             = REUSE
           socket_type  = stream       
           wait              = no
           user              = root
           server           = /usr/sbin/in.telnetd
           log_on_failure    += USERID
           only_from    = 192.168.1.0/24
    }
    [root@serv01 xinetd.d]# /etc/init.d/xinetdrestart
    Stopping xinetd:                                          [  OK  ]
    Starting xinetd:                                          [  OK  ]
     
    [root@serv02 .ssh]# telnet 192.168.1.11
    Trying 192.168.1.11...
    Connected to 192.168.1.11.
    Escape character is '^]'.
    Red Hat Enterprise Linux Server release 6.1(Santiago)
    Kernel 2.6.32-131.0.15.el6.x86_64 on anx86_64
    login: hongyi
    Password:
    Last login: Tue Aug  6 23:46:23 from 192.168.1.13
    [hongyi@serv01 ~]$
     
    [root@serv03 .ssh]# telnet 192.168.1.11
    Trying 192.168.1.11...
    Connected to 192.168.1.11.
    Escape character is '^]'.
    Red Hat Enterprise Linux Server release 6.1(Santiago)
    Kernel 2.6.32-131.0.15.el6.x86_64 on anx86_64
    login: hongyi
    Password:
    Last login: Tue Aug  6 23:48:15 from 192.168.1.12
    [hongyi@serv01 ~]$

## 五 telnet允许或者禁止在某个时间段访问（access\_times、deny\_time） ##

#telnet允许或者禁止在某个时间段访问，可以通过access_times、deny_time参数控制。比如：
    #access_times 8:00-17:30
    #deny_time 15:00-17:30

## 六 参考资料 ##

[http://baike.baidu.com/view/44255.htm][http_baike.baidu.com_view_44255.htm]

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