CCNA 2 Module 4 Learning about Devices
Cisco Discovery Protocol (CDP) • Builds a basic picture of the network • Allows 2 systems to learn about each other • For neighbor discovery • Only shows information about directly connected neighbors • It is a layer 2 protocol • Connects physical media and network layer protocols • Media Independent • Different L1 media types (LAN, Frame Relay, ATM…) • Protocol independent • Can have different L3 protocols (TCP/IP,IPX, Apple Talk...) • Runs on all Cisco equipment over the Subnetwork Access Protocol (SNAP)
Most recent release is CDP Version 2 (CDPv2) • Starts up automatically on router bootup • Must be running on all the neighbourhood devices • Each device sends periodic messages (advertisements) to multiple directly connected routers running CDP • Each device advertises: • at least one address at which it can receive Simple Network Management Protocol (SNMP) messages. • “time-to-live” or holdtime information, indicating the length of time that receiving devices should hold CDP information before discarding it. • each device also listens to periodic CDP messages sent by others in order to learn about neighboring devices.
Information obtained with CDP • show cdp neighbors displays information about • Networks directly connected to the router • Each CDP neighbor device using type length values (TLVs) • Information embedded in advertisements • Device ID • Local Interface • Holdtime • Capability • Platform • Port ID • VTP Management Domain Name (CDPv2 only) • Native VLAN (CDPv2 only) • Full/Half-Duplex (CDPv2 only)
Cdp info can be used to create a network map of the connected devices
Implementation, monitoring, and maintenance of CDP Note - By default CDP is globally enabled
Disabling CDP • use the no CDP run command in global configuration mode • If CDP is disabled globally, individual interfaces cannot be enabled for CDP.
Telnet • Allows connections to be made to remote hosts • An IOS EXEC command used to verify the application layer software between source and destination • The most complete test of connectivity • Works at the Application layer (7) • You can have up to 5 Telnet sessions • 0 - 4
Establishing and verifying a Telnet connection • Router>connect/Telnet <hostname>Router>connect/Telnet<ip address>Router>exit/logout • A hostname table or access to DNS for Telnet must be present for a name to work • Can be performed at either the user or privileged EXEC levels
If you can Telnet to one router and not another problem may be • Specific addressing • Naming • Access permission • The Ping command will check for physical connection
Ping to Test Connectivity • Ping • Sends echo packet to destination host • Waits for an echo reply packet from that destination • Results from echo protocol can help evaluate • Path-to-host reliability • Delays over the path • Whether destination host can be reached • Is destination host functioning
Performed at either • User EXEC mode • Privileged EXEC mode • Ping uses ICMP echo request • “!” indicates a successful echo. • Periods (.) indicates router timed while waiting • “ * ”, no connection
Troubleshooting IP addressing issues • IP addressing is a big problem • ping verifies • Hardware connection • and IP address of the network layer • telnet verifies • Application layer software between source and destination • 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.