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。
环境
- Cisco Packet Tracer 5.3
操作
操作：按照如图所示连接拓扑图
（1）配置PC IPPC0 设置 192.168.1.2/24 PC1 设置 192.168.1.3/24（2）配置交换机VLAN1 IP
/* part1 为vlan配置ip并开启vlan */ Switch>enable Switch#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Switch(config)#interface vlan 1 Switch(config-if)#ip address 192.168.1.1 255.255.255.0 Switch(config-if)#no shutdown %LINK-5-CHANGED: Interface Vlan1, changed state to up %LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan1, changed state to up Switch(config-if)# /* Part2 查看已配置的IP */ Switch(config-if)#^Z Switch# %SYS-5-CONFIG_I: Configured from console by console Switch#show running-config ... interface Vlan1 ip address 192.168.1.1 255.255.255.0 /* Part3 开启Vlan */ Switch#conf t Enter configuration commands, one per line. End with CNTL/Z. Switch(config)#interface vlan 1 Switch(config-if)#no shutdown /* Part4 查看Vlan状态 */ Switch(config-if)#^Z Switch# %SYS-5-CONFIG_I: Configured from console by console Switch#show interfaces vlan 1 Vlan1 is up, line protocol is up ...（3）配置交换机本地登录口令
/* Part 1 设置明文密码*/ Switch#conf t Enter configuration commands, one per line. End with CNTL/Z. Switch(config)#enable password 123 // 注：取消密码可用no enable password /* Part 2查看设置的密码 */ Switch(config)#^Z Switch# %SYS-5-CONFIG_I: Configured from console by console Switch#show running-config ... enable password 123 ...（4）配置交换机远程登陆及验证
Switch#conf t Enter configuration commands, one per line. End with CNTL/Z. Switch(config)#line vty 0 Switch(config-line)#password 123 //（Telnet密码为123） Switch(config-line)#login local //（login是开启远程登录密码验证，login local不但要求TELNET密码，还要求提供用户名） Switch(config-line)#（5）添加可远程登陆交换机的用户
/* Part 1 添加用户 */ Switch#conf t Enter configuration commands, one per line. End with CNTL/Z. Switch(config)#line vty 0 Switch(config-line)#password 123 Switch(config-line)#login local Switch(config-line)# Switch(config-line)#exit Switch(config)#username admin password admin /* Part 2 查看添加的用户 */ Switch(config)#exit Switch# %SYS-5-CONFIG_I: Configured from console by console Switch#show running-config ... username admin password 0 admin ...
（6）测试连接
// 在PC0的CMD中测试
/* Part 1 Ping交换机 */
PC>ping 192.168.1.1
Pinging 192.168.1.1 with 32 bytes of data:
Reply from 192.168.1.1: bytes=32 time=5ms TTL=255
Reply from 192.168.1.1: bytes=32 time=5ms TTL=255
Reply from 192.168.1.1: bytes=32 time=6ms TTL=255
Reply from 192.168.1.1: bytes=32 time=6ms TTL=255
Ping statistics for 192.168.1.1:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 5ms, Maximum = 6ms, Average = 5ms
/* Part 2 Telnet 连接交换机 */
PC>telnet 192.168.1.1
Trying 192.168.1.1 ...Open
User Access Verification
Username: admin
Password:
Switch>（7）配置多用户连接
// 在PC0连接的前提下，再使用PC1尝试连接
/* Part 1 PC1 Ping Switch */
PC>ping 192.168.1.1
Pinging 192.168.1.1 with 32 bytes of data:
Request timed out.
Reply from 192.168.1.1: bytes=32 time=6ms TTL=255
Reply from 192.168.1.1: bytes=32 time=6ms TTL=255
Reply from 192.168.1.1: bytes=32 time=5ms TTL=255
Ping statistics for 192.168.1.1:
Packets: Sent = 4, Received = 3, Lost = 1 (25% loss),
Approximate round trip times in milli-seconds:
Minimum = 5ms, Maximum = 6ms, Average = 5ms
/* Part 2 PC1 Telnet 连接Swithc */
PC>telnet 192.168.1.1
Trying 192.168.1.1 ...Open
[Connection to 192.168.1.1 closed by foreign host]
// 连接失败，因为交换机vty设置只能同时打开一个会话，下面设置一下，使两台PC可同时访问
/* Part 3 修改Tenlet配置 */
// 可直接在PC0直接进行
Switch#conf t
Enter configuration commands, one per line. End with CNTL/Z.
Switch(config)#line vty 0 1
Switch(config-line)#password 123
Switch(config-line)#^Z
/* Part 4 重新尝试Part 2 */
PC>telnet 192.168.1.1
Trying 192.168.1.1 ...Open
User Access Verification
Password:
Switch>
// 成功