cdp traffic
  • show debugging
  • debug cdp adjacency
  • debug cdp events
  • debug cdp ip
  • debug cdp packets
  • cdp timer
  • cdp holdtime
  • show cdp
    • Lab Activity Lab Exercise: Using CDP Commands In this lab, the students will use CDP commands to obtain information about neighboring networks and devices. Lab Activity e-Lab Activity: Address Resolution Protocol In this lab, the students will use the show ARP command, which is another means of learning about neighboring devices. Lab Activity e-Lab Activity: CDP Neighbors In this lab, the students will use Cisco Discovery Protocol (CDP) commands. Web Links Configuring Cisco Discovery Protocol (CDP) http://www.cisco.com/en/US/products/sw/ iosswrel/ps1831/products_configuration_guide_ chapter09186a00800ca66d.html#xtocid7
    Content 4.2 Getting Information about Remote Devices 4.2.1 Telnet 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 provides a network terminal or remote login capability. 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. 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. It should be noted that verifying application layer connectivity is a byproduct of Telnet. The main use of Telnet is remote connection to network devices. Telnet is a simple and universal application program.
    Content 4.2 Getting Information about Remote Devices 4.2.2 Establishing and verifying a Telnet connection The Telnet IOS EXEC command allows a user to Telnet from one Cisco device to another. With Cisco's implementation of TCP/IP, it is not necessary to enter the command connect or telnet to establish a Telnet connection. The hostname or the IP address of the remote router may be entered. To end a Telnet session, use the EXEC commands exit or logout. To initiate a Telnet session any of the following alternatives can be used: Denver>connect paris
    Denver>paris
    Denver>131.108.100.152
    Denver>telnet paris A hostname table or access to DNS for Telnet must be present for a name to work. Otherwise, the IP address of the remote router must be entered. Telnet can be used to perform a test to determine whether or not a remote router can be accessed. As shown in Figure , if Telnet is used successfully to connect the York router to the Paris router, then a basic test of the network connection is successful. This operation can be performed at either the user or privileged EXEC levels. If remote access can be obtained through another router, then at least one TCP/IP application can reach the remote router. A successful Telnet connection indicates that the upper-layer application functions properly. If Telnet to one router can occur, but failure to another router occurs, it is likely that specific addressing, naming, or access permission problems caused the Telnet failure. It is possible that the problem exists on this router or on the router that failed as a Telnet target. In this case, the next step is to try ping, which is covered later in this lesson. Ping allows testing of end-to-end connections at the network layer. Once the Telnet is completed, log off the host. The Telnet connection will terminate after ten minutes of inactivity by default or when the exit command at the EXEC prompt is entered. Lab Activity Lab Exercise: Establishing and Verifying a Telnet Connection In this lab, the students will establish a Telnet connection to a remote router and verify that the application layer between source and destination is working properly. Web Links A Telnet Tutorial http://oregonstate.edu/aw/ tutorials/telnet/
    Content 4.2 Getting Information about Remote Devices 4.2.3 Disconnecting and suspending Telnet sessions One important feature of the Telnet command is the suspend feature. However, one potential problem exists when a Telnet session is suspended and the Enter key is pressed. Cisco IOS software resumes the connection to the most recently suspended Telnet connection. The Enter key is used frequently. With a suspended Telnet session, it is possible to reconnect to another router. This is dangerous when changes are made to the configuration or using EXEC commands. Always pay particular attention to what router is being used when utilizing the suspended Telnet feature.A session is suspended for a limited time, to resume a Telnet session that has been suspended, just press Enter. The command show sessions will show what Telnet sessions are taking place. The procedure for disconnecting a Telnet session is as follows: The procedure for suspending a Telnet session is as follows: Lab Activity Lab Exercise: Suspending and Disconnecting Telnet Sessions In this lab, the students will establish a Telnet session with a remote router and then suspend and re-establish a telnet session.
    Content 4.2 Getting Information about Remote Devices 4.2.4 Advanced Telnet operation There may be several concurrent Telnet sessions open. A user may switch back and forth between these sessions. The number of open sessions that are allowed at one time is defined by the session limit command.To switch between sessions by escaping one session and resuming a previously opened session, use the commands shown in Figure . A new connection can be made while at the EXEC prompt. The 2500 series routers are limited to five sessions. Multiple Telnet sessions can be used and suspended by using the Ctrl-Shift-6, then x sequence. The session can be resumed by using the Enter key. If the Enter key is used, the Cisco IOS Software resumes the connection to the most recently suspended Telnet connection. If the resume command is used it requires a connection ID. The connection ID is shown by using the show sessions command. Lab Activity Lab Exercise: Advanced Telnet Operations This lab is to use the telnet command to remotely access other routers.
    Content 4.2 Getting Information about Remote Devices 4.2.5 Alternative connectivity tests As an aid to diagnosing basic network connectivity, many network protocols support an echo protocol. 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, and whether the host can be reached or is functioning. This is a basic testing mechanism. This operation can be performed at either the user or privileged EXEC modes.The ping target 172.16.1.5 in Figure responded successfully to all five datagrams sent. The exclamation points (!) indicate each successful echo. If one or more periods (.) are received instead of exclamations on the display, 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).