Sunday, January 21, 2018

IAM Search

Routers and Routing Basics - Learning About Other Devices

Who Else Is Out There?

• Cisco Discovery Protocol (CDP)

– Layer 2 protocol that transmits to discover information about directly connected Cisco devices.

– Media and protocol independent.

– Transmits type length values (TLVs) embedded in CDP advertisements over Subnetwork Access Protocol (SNAP)

• CDP is enabled by default in IOS 10.3 and later.


Discovering Your Network

• Router# show cdp neighbors

• CDPv1 available on IOS 10.3 to 12.0(3)T

– Includes reporting on device ID, what interface and port it’s directly connected to, capability, and platform.

• CDPv2 available from IOS 12.0(3)T and later

– Includes reporting on VTP management domain membership, native VLAN, and half/full duplex mode.

Take Command of CDP

• Router# show cdp entrycdp-device-name

• Router# show cdp traffic

Time to Test with Telnet

• CDP only gathers information about other devices

• Telnet allows us to establish virtual terminal sessions with other devices.

– Provides remote login capabilities on telnet-enabled devices via virtual terminal lines.

• Facilitates remote device management.

– Operates at Application Layer (OSI Layer 7)

• Most complete form of connection verification available.

Making the Connection?

• A successful telnet session to a remote router indicates functionality at all layers.

– Possible issues include access permissions, naming, logical addressing.

• Successful pingusing router name indicates name resolved correctly.

– Incorrect access permissions

• Successful ping using router logical address indicates functioning path determination.

– Incorrect entry in host name table.

• Consider using traceroute to test all hops between source and destination.

– Ping tests end-to-end connectivity.

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