CCNA2

1
CCNA2

• Module 4

2
Discovering and Connecting to Neighbors

• Enable and disable CDP
• Use the show cdp neighbors command
• Determine which neighboring devices are connected
  to which local interfaces
• Gather network address information about
  neighboring devices using CDP

3
Discovering and Connecting to Neighbors

• Establish a Telnet connection
• Verify a Telnet connection
• Disconnect from a Telnet session
• Suspend a Telnet session
• Perform alternative connectivity tests
• Troubleshoot remote terminal connections

4
Discovering and Connecting to Neighbors

• Cisco Discovery Protocol (CDP) is a Layer 2
  protocol that connects lower physical media and
  upper network layer protocols
• CDP is used to obtain information about
  neighboring devices, such as the types of devices
  connected
• CDP is media and protocol independent, and runs
  on all Cisco equipment

5
Discovering and Connecting to Neighbors

• When a Cisco device boots up, CDP starts up
  automatically and allows the device to detect
  neighboring devices that are also running CDP
• It runs over the data link layer and allows two
  systems to learn about each other
• Each device configured for CDP sends periodic
  messages, known as advertisements, to multiple
  routers.

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Discovering and Connecting to Neighbors

• 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
• Additionally, each device listens to periodic CDP
  messages sent by others in order to learn about
  neighboring devices

7
Discovering and Connecting to Neighbors

• The primary use of CDP is to discover all Cisco
  devices that are directly connected to a local
  device
• Each router that is running CDP exchanges
  protocol information with its neighbors
• The administrator uses the show cdp neighbors
  command to display information about the networks
  directly connected to the router
• CDP provides information about each CDP neighbor
  device by transmitting type length values (TLVs),
  which are blocks of information embedded in CDP
  advertisements

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Discovering and Connecting to Neighbors
9
Discovering and Connecting to Neighbors

• Notice that the lowest router in the figure is
  not directly connected to the administrators
  console router. To obtain CDP information about
  this device, the administrator would need to
  Telnet to a router that is directly connected to
  this device.

10
Discovering and Connecting to Neighbors

• The following commands are used to implement,
  monitor, and maintain CDP information
• cdp run
• cdp enable
• clear cdp counters
• show cdp
• show cdp entry device-nameprotocol
  version
• show cdp interface type number
• show cdp neighbors type number detail

11
Discovering and Connecting to Neighbors

• The cdp run command is used to enable CDP
  globally on the router. By default, CDP is
  globally enabled. The cdp enable command is used
  to enable CDP on a particular interface
• CDP could be enabled on each of the devices
  interfaces by using the cdp enable command.

12
Discovering and Connecting to Neighbors

• Though a CDP frame can be small, it can retrieve
  a great deal of useful information about
  connected neighboring Cisco devices
• This information can be used to create a network
  map of the connected devices. Devices connected
  to neighboring devices can be discovered by using
  Telnet to connect to the neighbors, and using the
  show cdp neighbors command to discover what
  devices are connected to those neighbors.

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Discovering and Connecting to Neighbors

• To disable CDP at the global level, use the no
  CDP run command in global configuration mode.
  If CDP is disabled globally, individual
  interfaces cannot be enabled for CDP

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Discovering and Connecting to Neighbors
15
Discovering and Connecting to Neighbors

• Telnet is a virtual terminal protocol that is
  part of the TCP/IP protocol suite. It allows
  connections to be made to remote hosts.
• Telnet is an IOS EXEC command used to verify the
  application layer software between source and
  destination. This is the most complete test
  mechanism available.
• 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

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Discovering and Connecting to Neighbors

• A router can have multiple simultaneous incoming
  Telnet sessions. The range zero through four is
  used to specify five VTY or Telnet lines. These
  five incoming Telnet sessions could take place at
  one time.

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Discovering and Connecting to Neighbors
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Discovering and Connecting to Neighbors

• To initiate a Telnet session any of the following
  alternatives can be used
• Denvergtconnect parisDenvergtparisDenvergt131.108.1
  00.152Denvergttelnet paris

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Discovering and Connecting to Neighbors
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Discovering and Connecting to Neighbors
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Discovering and Connecting to Neighbors

• 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.

22
Discovering and Connecting to Neighbors

• 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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Discovering and Connecting to Neighbors

• The traceroute command is the ideal tool for
  finding where data is being sent in a network
• The traceroute command is similar to the ping
  command, except that instead of testing
  end-to-end connectivity, traceroute tests each
  step along the way.

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Discovering and Connecting to Neighbors
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Discovering and Connecting to Neighbors

• 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.