Learning About Other Devices

1
Learning About Other Devices

• Module 4
• CCNA 2 - Version 3.0

2
Introduction to CDP

• Cisco Discovery Protocol (CDP)
• Layer 2 protocol
• connects lower physical media and upper network
  layer protocols
• used to obtain information about neighboring
  devices such as
• the types of devices connected
• the router interfaces they are connected to
• the interfaces used to make the connections
• the model numbers of the devices
• media and protocol independent
• runs on all Cisco equipment over the Subnetwork
  Access Protocol (SNAP)

3
CDP Introduction

• CDP starts up automatically
• Allows devices to detect neighboring devices that
  are also running CDP
• CDP runs over the data link layer and allows two
  systems to learn about each other, even if they
  are using different network layer protocols
• CDP Version 2 (CDPv2) is the most recent release
  of the protocol
• Cisco IOS (Release 12.0(3)T or later) supports
  CDPv2

4
CDP Introduction

• Each device configured for CDP sends periodic
  messages to multiple routers - known as
  advertisements
• Each device advertises at least one address at
  which it can receive Simple Network Management
  Protocol (SNMP) messages
• The advertisements also contain time-to-live or
  holdtime information, indicating the length of
  time that receiving devices should hold CDP
  information before discarding it

5
Information obtained from CDP

• CDP provides information about each CDP neighbor
  device by transmitting type length values (TLVs)
• TLVs are blocks of information embedded in CDP
  advertisements.
• TLVs displayed by the show cdp neighbors command
• Device ID
• Local Interface
• Holdtime
• Capability
• Platform
• Port ID
• VTP Management Domain Name (CDPv2 only)
• Native VLAN (CDPv2 only)
• Full/Half-Duplex (CDPv2 only)

6
CDP Commands

• cdp run
• used to enable CDP globally on the router
• By default, CDP is globally enabled
• Note Use the no cdp run command to disable CDP
  globally
• cdp enable
• used to enable CDP on a particular interface
• On Cisco IOS Release 10.3 or higher, CDP is
  enabled by default on all supported interfaces
• Note Use the no cdp enable command to disable
  CDP on an interface

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CDP Commands Show CDP Traffic and Clear CDP
Counters
Shows CDP counters
8
CDP Commands Show CDP
Shows advertisement info
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CDP Commands Show CDP Entry
Shows info about a specific neighbor
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CDP Commands Show CDP Interface
Shows info on interfaces in which CDP is enable
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CDP Commands Show CDP Neighbors
Displays info on the device thats been discovered
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Creating a Network MapUsing CDP

• Information gathered through CDP can be used to
  create a network map of the connected devices
• How do you find information about devices not
  directly connected?
• Telnet to connect to the neighbors
• Issue the show cdp neighbors command to discover
  what devices are connected to those neighbors

13
Troubleshooting CDP
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Telnet is

• Virtual terminal protocol - part of the TCP/IP
  protocol suite
• Main use is is for remote login capability
• Used to verify the application layer software
  between source and destination
• The most complete test mechanism
• Telnet functions at the application layer of the
  OSI model
• Telnet depends on TCP to guarantee the correct
  and orderly delivery of data between the client
  and server.
• A router can have up to 5 multiple simultaneous
  incoming Telnet sessions
• The range zero through four is used to specify
  five VTY or Telnet lines

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Initiating a Telnet Session

• To initiate a Telnet session any of the following
  alternatives can be used
• Denvergtconnect paris
• Denvergtparis
• Denvergt131.108.100.152
• Denvergttelnet paris
• This operation can be performed at either the
  user or privileged EXEC levels

16
Disconnecting and Suspending Telnet Sessions
Note The Telnet connection will terminate after
ten minutes of inactivity by default or when the
exit command at the EXEC prompt is entered
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Advanced Telnet Operations

• Several concurrent Telnet sessions can be open
  (2500 series is limited to 5)
• A user may switch back and forth between these
  sessions
• Ctrl-Shift-6, then x sequence suspends a session
• Pressing enter takes the user back to the most
  recently suspended Telnet session
• The resume command with a Connection ID goes to a
  specific suspended session
• The number of open sessions that are allowed at
  one time is defined by the session limit command

Suspends a Telnet session
Connection ID
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Other Connectivity Tests PING

• Echo protocols are used to test whether protocol
  packets are being routed
• The ping command sends a packet to the
  destination host and then waits for a reply
  packet from that host
• Results from this echo protocol can help
  evaluate
• the path-to-host reliability
• delays over the path
• whether the host can be reached or is functioning
• This operation can be performed at either the
  user or privileged EXEC modes

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Other Connectivity Tests PING

• The exclamation points (!) indicate each
  successful echo
• Periods (.) means the application on the router
  timed out waiting for a given packet echo from
  the ping target
• The ping user EXEC command can be used to
  diagnose basic network connectivity
• The command ping uses ICMP (Internet Control
  Message Protocol)

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Other Connectivity Tests Traceroute

• The traceroute command is the ideal tool for
  finding where data is being sent in a network
• traceroute tests each step along the way from
  source to destination
• This operation can be performed at either the
  user or privileged EXEC levels
• If one of these routers is unreachable, three
  asterisks () will be returned instead of the
  name of the router
• The traceroute command will continue attempting
  to reach the next step until the Ctrl-Shift-6
  escape sequence is used.

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Troubleshooting IP Addressing Issues

• Addressing problems are the most common problems
  that occur on IP networks. To perform
  address-related troubleshooting
• ping uses the ICMP protocol to verify the
  hardware connection and the IP address of the
  network layer. This is a basic testing mechanism
• telnet verifies the application layer software
  between source and destination. This is the most
  complete test mechanism available
• traceroute allows the location of failures in the
  path from the source to the destination. Trace
  uses Time to Live values to generate messages
  from each router along the path. 

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Learning About Other Devices
THE END

• Module 4
• CCNA 2 - Version 3.0