learn about other devices.ppt
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1Version 3.1
Module 4Learning About
Other Devices
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2Version 3.1
Cisco Discovery Protocol
A Layer 2 protocol
Obtains information about neighboring Ciscodevices(interfaces, model numbers)
CD !ill discover directly connected Cisco devicesregardless
of !hich Layer " and # protocol suite they run $uns over the %ubnet!or& Access rotocol (%'A)
CDv2 is most recent release
%tarts automatically !hen a device boots up enabled by
default ach Cisco device sendsperiodic advertisementsto multiple
routers (and listens for other messages)
nables net!or& administrators to access a summary of !hat
the configurations loo& li&e on other directly connected routers*
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3Version 3.1
show cdp neighborscommand
Device identifiers - the configured host name of the routerand domain name (if any).
ddress list - t least one !rotocol for "#MP$ u! to one
address for each !rotocol su!!orted.
Port identifier - %thernet &$ %thernet 1$ "erial &$ etc.
Ca!a'ilities list - does the device acts as a 'ridge as ell as
a router
Version - *nformation such as that !rovided 'y the local
command sho version.
Platform - +he device hardare !latform, for eam!le$ Cisco
&&&.
Router#show cdp neighbors (displays CDP updates)
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4Version 3.1
+y!e /ength Value (+/V)+L is simply a piece of information in a CD advertisement
Device *D *dentifies the device name
/ocal interface Contains a list of netor0 addresses of 'oth receivingand transmitting devices
Port *D *dentifies the !ort on hich the CDP !ac0et is sent
Ca!a'ilities Descri'es the devices ca!a'ility 2 i.e. 2 a sitch
Version "oftare release version on hich the device is running
Platform ardare !latform 2 i.e. 2 Cisco 5&&
*P #etor0 Prefi list of netor0 !refies to hich the sending devicecan forard *P !ac0ets
oldtime +he amount of time$ in seconds$ the device directs theneigh'or to hold a CDP advertisement 'efore discardingit
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5Version 3.1
CDP
-f an administrator needs CD information from a Cisco
router that is not directly, then a +elnet session can be
established to connect to another Cisco device that is
connected to the device he needs the information on*
'eeds CD info on this
router, he could telnet to
router above to run sho!
CD neighbors command
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6Version 3.1
CDP Commands
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7/217Version 3.1
%na'ling CDP on a 6outer
To enable CDP, use the
cdp run
global confguration
command. CDP is on by deault. Use the no
orm o
this command to disable CDP.
Router(config)#cdp run
+o enable Cisco Discovery rotocol (CD) on an interface,
use the cdp enableinterface configuration command* .se
the noform of this command to disable CD on an interface*
CD is enabled by default on all supported interfaces*
Router(config)#interface serial 0/0
Router(config-if)#cdp enable
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clear cd! counters
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Version 3.1
sho cd!
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Version 3.1
sho cd! entry
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Version 3.1
sho cd! interface
"tatus of the
carrier detect
signal
7ee!alive
messages
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Version 3.1
show cdp neighbors
Router#show cdp neighbors detail !ill
also give the IP addressof the neighboring Ciscodevice
7no this
out!ut8888
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Version 3.1
9ther cd! commands
show cdp traffic2 sho!s number of pac&ets sent and
received
cdp timer/ specifies ho! often the -O% sends CD
updates
debug cdp/ for debugging all aspects of cdp
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Version 3.1
+elnet
Part of +CP:*P
suite
6outers have ;
virtual terminal
sessions
Main use is
remote
connection to
netor0
devices
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15Version 3.1
%na'ling CDP on a 6outer
To initiate a Telnet session any o the ollowing
alternatives can be used:
Dener!connect paris
Dener!paris
Dener!""$"0%$"00$"&'
Dener!telnet ""$"0%$"00$"&'
Dener!telnet paris
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16Version 3.1
6eo!ening a sus!ended +elnet session
0ultiple +elnet sessions can be used and suspended by using
the Ctrl-"hift-5, then se1uence*
+hen the session can be resumed by using the nter &ey*
-f the nter &ey is used to resume the session, then Cisco -O%resumes the most recently suspended session*
ou can also use the resumecommand to start up a previous
session, but to do that you must &no! the connection -D*
+o get the connection -D, use the show sessions
command
first, so you can resume the correct session*
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17Version 3.1
6eo!ening a sus!ended +elnet session
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18Version 3.1
+hepingCommand
Ping is a 'asic *nternet !rogram that lets you verify that a!articular *nternet address eists and can acce!t re
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19Version 3.1
>hat Ping can tell you
ing places a uni1ue se1uence number on each pac&et ittransmits, and reports !hich se1uence numbers it receives
bac&* +hus, it can be determine if pac&ets have been dropped,
duplicated, or reordered*
ing places a timestamp in each pac&et, !hich is echoed bac&
and can easily be used to compute ho! long each pac&et
e3change too& / the $ound +rip +ime ($++)*
ing reports other -C0 messages that might other!ise get
buried in the system soft!are* -t reports, for e3ample, if a router
is declaring the target host unreachable*
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20Version 3.1
>hat Ping can not tell you
%ome routers may silently discard undeliverable pac&ets*Others may believe a pac&et has been transmitted successfully
!hen it has not been* (+his is especially common over
thernet, !hich does not provide lin&/layer ac&no!ledgments)
+herefore, ping may not al!ays provide reasons !hy pac&ets
go unans!ered*
ing can not tell you !hy a pac&et !as damaged, delayed, or
duplicated* -t can not tell you !here this happened either,
although you may be able to deduce it*
ing can not give you a blo!/by/blo! description of every host
that handled the pac&et and everything that happened at every
step of the !ay* -t is an unfortunate fact that no soft!are can
reliably provide this information for a +C4- net!or&*
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traceroute
traceroute is a utility that records the route through the*nternet 'eteen your com!uter and a s!ecified destination
com!uter
*t also calculates and dis!lays the amount of time each ho!
too0
traceroute tests each ste! (router) along the ay
*f one router in the !ath is unreacha'le$ three asteris0s (???)
ill 'e returned instead of the name of the router
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