1. 1 Version 3.1 Module 4 Learning About Other Devices

2. 2 Version 3.1 Cisco Discovery Protocol A Layer 2 protocol Obtains information about neighboring Cisco devices (interfaces, model numbers) CDP will discover directly connected Cisco devices regardless of which Layer 3 and 4 protocol suite they run Runs over the Subnetwork Access Protocol (SNAP) CDPv2 is most recent release Starts automatically when a device boots up – enabled by default Each Cisco device sends periodic advertisements to multiple routers (and listens for other messages) Enables network administrators to access a summary of what the configurations look like on other directly connected routers.

3. 3 Version 3.1 show cdp neighbors command  Device identifiers - the configured host name of the router and domain name (if any).  Address list - At least one protocol for SNMP, up to one address for each protocol supported.  Port identifier - Ethernet 0, Ethernet 1, Serial 0, etc.  Capabilities list - does the device acts as a bridge as well as a router?  Version - Information such as that provided by the local command show version.  Platform - The device hardware platform: for example, Cisco 7000. Router#show cdp neighbors (displays CDP updates)

4. 4 Version 3.1 Type Length Value (TLV) TLV is simply a piece of information in a CDP advertisement Device IDIdentifies the device name Local interfaceContains a list of network addresses of both receiving and transmitting devices Port IDIdentifies the port on which the CDP packet is sent CapabilitiesDescribes the device’s capability – i.e. – a switch VersionSoftware release version on which the device is running PlatformHardware platform – i.e. – Cisco 2600 IP Network PrefixA list of network prefixes to which the sending device can forward IP packets HoldtimeThe amount of time, in seconds, the device directs the neighbor to hold a CDP advertisement before discarding it

5. 5 Version 3.1 CDP If an administrator needs CDP information from a Cisco router that is not directly, then a Telnet session can be established to connect to another Cisco device that is connected to the device he needs the information on. Needs CDP info on this router, he could telnet to router above to run show CDP neighbors command

6. 6 Version 3.1 CDP Commands

7. 7 Version 3.1 Enabling CDP on a Router To enable CDP, use the cdp run global configuration command. CDP is on by default. Use the no form of this command to disable CDP. Router(config)#cdp run To enable Cisco Discovery Protocol (CDP) on an interface, use the cdp enable interface configuration command. Use the no form of this command to disable CDP on an interface. CDP is enabled by default on all supported interfaces. Router(config)#interface serial 0/0 Router(config-if)#cdp enable

8. 8 Version 3.1 clear cdp counters

9. 9 Version 3.1 show cdp

10. 10 Version 3.1 show cdp entry

11. 11 Version 3.1 show cdp interface Status of the carrier detect signal Keepalive messages

12. 12 Version 3.1 show cdp neighbors Router#show cdp neighbors detail will also give the IP address of the neighboring Cisco device Know this output!!!!

13. 13 Version 3.1 Other cdp commands show cdp traffic – shows number of packets sent and received cdp timer - specifies how often the IOS sends CDP updates debug cdp - for debugging all aspects of cdp

14. 14 Version 3.1 Telnet Part of TCP/IP suite Routers have 5 virtual terminal sessions Main use is remote connection to network devices

15. 15 Version 3.1 Enabling CDP on a Router 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 131.108.100.152 Denver>telnet paris

16. 16 Version 3.1 Reopening a suspended Telnet session Multiple Telnet sessions can be used and suspended by using the Ctrl-Shift-6, then x sequence. Then the session can be resumed by using the Enter key. If the Enter key is used to resume the session, then Cisco IOS resumes the most recently suspended session. You can also use the resume command to start up a previous session, but to do that you must know the connection ID. To get the connection ID, use the show sessions command first, so you can resume the correct session.

17. 17 Version 3.1 Reopening a suspended Telnet session

18. 18 Version 3.1 The ping Command Ping is a basic Internet program that lets you verify that a particular Internet address exists and can accept requests If, for example, a user cannot ping a host, then the user will be unable to use the File Transfer Protocol (FTP) to send files to that host Ping can also be used with a host that is operating to see how long it takes to get a response back

19. 19 Version 3.1 What Ping can tell you  Ping places a unique sequence number on each packet it transmits, and reports which sequence numbers it receives back. Thus, it can be determine if packets have been dropped, duplicated, or reordered.  Ping places a timestamp in each packet, which is echoed back and can easily be used to compute how long each packet exchange took - the Round Trip Time (RTT).  Ping reports other ICMP messages that might otherwise get buried in the system software. It reports, for example, if a router is declaring the target host unreachable.

20. 20 Version 3.1 What Ping can not tell you  Some routers may silently discard undeliverable packets. Others may believe a packet has been transmitted successfully when it has not been. (This is especially common over Ethernet, which does not provide link-layer acknowledgments) Therefore, ping may not always provide reasons why packets go unanswered.  Ping can not tell you why a packet was damaged, delayed, or duplicated. It can not tell you where this happened either, although you may be able to deduce it.  Ping can not give you a blow-by-blow description of every host that handled the packet and everything that happened at every step of the way. It is an unfortunate fact that no software can reliably provide this information for a TCP/IP network.

21. 21 Version 3.1 traceroute traceroute is a utility that records the route through the Internet between your computer and a specified destination computer It also calculates and displays the amount of time each hop took traceroute tests each step (router) along the way If one router in the path is unreachable, three asterisks (***) will be returned instead of the name of the router

22. 22 Version 3.1 Module 4 Learning About Other Devices END