Cisco Discovery Protocol

Cisco Discovery Protocol

Router#sssshhohhowoowww ccccddpddppp Displays global CDP information (such as timers) Router#sssshhohhowoowww ccccddpddppp nnnneeieeigiiggghhhhbbobboroorrrssss Displays information about

neighbors

Router#sssshhohhowoowww ccccddpddppp nnnneeieeigiiggghhhhbbobboroorrrssss ddeddeeettttaaaaiiliilll Displays more detail about neighbor device

Router#sssshhohhowoowww ccccddpddppp eeeenntnntrttrrryyyy wwowwooorrrrdddd Displays information about device named word

Router#sssshhohhowoowww ccccddpddppp eeeenntnntrttrrryyyy **** Displays information about all devices

Router#sssshhohhowoowww ccccddpddppp iiiinntnntetteeerrrrffaffacaaccceeee Displays info about interfaces that have CDP running Router#sssshhohhowoowww ccccddpddppp iiiinntnntetteeerrrrffaffacaaccceeee x Displays info about specific

interface x running CDP Router#sssshhohhowoowww ccccddpddppp ttttrrarrafaafffffffiiciiccc Displays traffic info—packets

in/out/version

Router(config)#ccccddddpp pp hhhhoooolldlldtddtttiiiimmmmee xee Changes length of time to keep CDP packets

Router(config)#ccccddddpp pp ttttiiiimmemmereerrr x Changes how often CDP updates are sent

Router(config)#ccccddddpp pp rrrruuuunnnn Enables CDP globally (on by default)

Router(config)#nnnnoooo ccccddddpppp rrurruuunnnn Turns off CDP globally Router(config-if)#ccccddddpppp eeneennnaaaabbbbllelleee Enables CDP on a specific

interface

168 CDP

CAUTION: Although CDP is an excellent source of information to you the net-work administrator, is it a potential security risk if a hacker gains access to one of your systems. The information that you gain through CDP is also gained by the hacker.

After you have used CDP to gather your information in a production environ-ment, turn it off to thwart any bad people from using it for no good.

Router(config-if)#nnnnoooo ccdccdddpppp eeneennnaaaabbbbllelleee Turns off CDP on a specific interface

Router#cclcclelleeeaaaarrrr ccccddddpppp ccccoooouuuunntnntetteeerrrrssss Resets traffic counters to 0 Router#cclcclelleeeaaaarrrr ccccddddpppp ttttaaaabbbbllelleee Deletes the CDP table Router#ddeddebeebbbuuuugggg ccccddddpppp aaaaddddjjjjaacaacecceeennnnccccyyyy Monitors CDP neighbor

information

Router#ddeddebeebbbuuuugggg ccccddddpppp eeeevvvveeeenntnntsttsss Monitors all CDP events Router#ddeddebeebbbuuuugggg ccccddddpppp iiiipppp Monitors CDP events

specifically for IP

Router#ddeddebeebbbuuuugggg ccccddddpppp ppppaaaacccckkekketeetttssss Monitors CDP packet-related information

CHAPTER 19

Telnet

This chapter provides information and commands concerning the following topics:

• Using Telnet to remotely connect to other devices

Telnet

The following five commands all achieve the same result—the attempt to connect remotely to the router named paris at IP address 172.16.20.1.

Any of the preceding commands lead to the following configuration sequence:

Denver>tttteeleelnllnnneeeetttt ppppaaaarrrriisiisss Enter if ip host command was used previously to create a mapping of an IP address to the word paris

Denver>tttteeleelnllnnneeeetttt 111177772222..1..1611666....220220.00...1111

Denver>ppppaaraarirriiissss Enter if ip host command is using default port #

Denver>ccccoonoonnnnnnneeeecccctt tt ppppaaaarrirrisiisss Denver>1111772772.22...11116666..2..2220000....1111

Paris> As long as vty password is set.

See Caution following this table

Paris>eeeexxxxiitiittt Terminates the Telnet session Denver>

Paris>llllooooggoggouoouuutttt Terminates the Telnet session Denver>

Paris>

ÇÍ6

x

Suspends the Telnet session, but does not terminate it Denver>

170 Telnet

CAUTION: The following configuration creates a big security hole. Never use it in a live production environment. Use it in the lab only!

Denver>

®

paris Paris>

Denver>rrerreseesssuuuummmmeeee Resumes the connection to paris

Paris>

Denver>ddiddisiisssccccoooonnnnnnnneeeecccctt tt ppppaaaarrirrisiisss Terminates the session to paris Denver>

Denver#sshsshohhooowwww ssesseeessssssssiioiiooonnnnssss Displays connections you opened to other sites Denver#sshsshohhooowwww uusuussseeeerrrrssss Displays who is connected

remotely to you

Denver#cclcclelleeeaaaarrrr lllliiiinnnnee ee x Disconnects remote user connected to you on line x Line number is listed in the output gained from the show users command

Denver(config)#lllliiniinnneeee vvtvvtyttyyy 0000 4444

Denver(config-line) ssesseseesssssssiiiioonoonnn----lllliimiimimmiiitttt x Limits the number of simultaneous sessions per vty line to x amount

Denver(config)#lllliiniinnneeee vvtvvtyttyyy 0000 4444 .

Denver(config-line)#nnonno oo ppppaaaasssssssswwwwoooorrdrrddd Remote user is not challenged when Telnetting to this device Denver(config-line)#nnonno oo llllooooggiggiiinnnn Remote user moves straight to

user mode

Telnet 171

NOTE: A device must have two passwords for a remote user to be able to make changes to your configuration:

• Line vty password (or have it explicitly turned off; see previous Caution)

• Enable or enable secret password

Without the enable or enable secret password, a remote user will only be able to get to user mode, not to privileged mode. This is extra security.

CHAPTER 20