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Cisco IOS Cookbook, 2nd Edition by Ian Brown, Kevin Dooley

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Using the Small Servers

Problem

You want to enable or disable router services like finger, echo, and chargen.

Solution

The finger application provides a remote way of seeing who is logged into the router. You can enable it with the ip finger global configuration command:

Router1#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Router1(config)#ip finger
Router1#

Every Cisco router also has a set of small TCP and UDP server applications that are sometimes useful for test purposes:

Router1#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Router1(config)#service tcp-small-servers
Router1(config)#service udp-small-servers
Router1(config)#end
Router1#

Discussion

The finger command is a simple utility that allows you to do the equivalent of a show users command on a remote router. Unix computers generally have a standard finger program that you can run as follows:

Freebsd% finger @Router1
[Router1]

    Line       User       Host(s)              Idle       Location
  66 vty 0     kdooley    idle                 00:22:47 freebsd
  67 vty 1     ijbrown    idle                    1d07h freebsd
* 68 vty 2                idle                 00:00:00 freebsd

  Interface      User        Mode                     Idle     Peer Address

Freebsd%

But you can also use the Telnet program, and connect to TCP port 79 to access the finger server as well. You can do this from another router, for example:

Router2#telnet 10.1.1.2 finger Trying 10.1.1.2, 79 ... Open Line User Host(s) Idle Location 66 vty 0 kdooley idle 00:24:14 freebsd 67 vty 1 ijbrown idle 1d07h freebsd * 67 vty 1 idle 00:00:00 10.2.2.2 Interface ...

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