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CCNA 2 v3.1 Module 4

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CCNA 2

Module 4

Learning about Devices

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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)

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• 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.

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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)

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• Cdp info can be used to create a network map of the connected devices

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Implementation, monitoring, and maintenance of CDP

Note - By default CDP is globally enabled

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Disabling CDP

• 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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Troubleshooting CDP

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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

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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

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• 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

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Disconnecting and suspending Telnet sessions

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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

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• 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

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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

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• 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.