我们将路由器的fa0/0ip：192.168.1.1，tftp的为192.168.1.2 ，从pc的超级终端进入路由器Terminal，就如我们在pc中开始---程序----附件---超级终端一样的。其实这个软件还是不错的，呵呵！在tftpserver中有很多关于路由器的ios的版本，我们可以进入超级终端之后用show version 查看版本,在这里我选择的是1841路由器敲入show version 之后我们可以看到：

Cisco IOS Software, 1841 Software (C1841-ADVIPSERVICESK9-M), Version 12.4(15)T1, RELEASE SOFTWARE (fc2)

Technical Support: http://www.cisco.com/techsupport

Copyright (c) 1986-2007 by Cisco Systems, Inc.

Compiled Wed 18-Jul-07 04:52 by pt_team

ROM: System Bootstrap, Version 12.3(8r)T8, RELEASE SOFTWARE (fc1)

System returned to ROM by power-on

System image file is "flash:c1841-advipservicesk9-mz.124-15.T1.bin"

这个flash是比较高点的版本了，可以模拟出vpn（我随后会把做好vpn与大家分享一下！）现在我要把它还原成低版本的。首先要确保tftp服务器与路由器能够ping通，然后我们升级ios了，具体如下：

首先进入特权模式Router#copy tftp: flash: （从tftp服务器上将ios拷贝到flash中）

Address or name of remote host []? 192.168.1.2（TFTP服务器的IP地址）

Source filename []? c1841-ipbase-mz.123-14.T7.bin（TFTP服务器上的原文件名）

Destination filename [c1841-advipservicesk9-mz.124-15.T1.bin]? c1841-ipbase-mz.123-14.T7.bin（路由器FLASH上的文件名）

Accessing tftp://192.168.1.2/c1841-ipbase-mz.123-14.T7.bin....

Loading c1841-ipbase-mz.123-14.T7.bin from 192.168.1.2: !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

[OK - 13832032 bytes]

13832032 bytes copied in 10.984 secs (86228 bytes/sec)

完成了然后我们show version 看看

Router#show flash: 

System flash directory:

File  Length   Name/status

  3   33591768 c1841-advipservicesk9-mz.124-15.T1.bin

  4   13832032 c1841-ipbase-mz.123-14.T7.bin

  2   28282    sigdef-category.xml

  1   227537   sigdef-default.xml

[47679619 bytes used, 16336765 available, 64016384 total]

63488K bytes of processor board System flash (Read/Write)

最后我们在全局模式中敲入

Router(config)#boot system flash c1841-ipbase-mz.123-14.T7.bin 

然后重启就行了

最后show version 看下

Router#show version 

Cisco IOS Software, 1841 Software (C1841-IPBASE-M), Version 12.3(14)T7, RELEASE SOFTWARE (fc2)

Technical Support: http://www.cisco.com/techsupport

Copyright (c) 1986-2006 by Cisco Systems, Inc.

Compiled Mon 15-May-06 14:54 by pt_team

ROM: System Bootstrap, Version 12.3(8r)T8, RELEASE SOFTWARE (fc1)

System returned to ROM by power-on

System image file is "flash:c1841-ipbase-mz.123-14.T7.bin"

我们可以将原来的ios删除掉,节省空间. 

以上就是ios的升级过程。