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CCNA 2: Routers and Routing Basics v3.1 Instructor Guide – Module 4
Copyright
©
2004, Cisco Systems, Inc.
4.1.2 Information obtained with CDP
CDP is used to collect information about directly-connected devices. The types of information
it collects are referred to as Type Length Values (TLVs). This TI includes a table that defines
each TLV. Certain types of information are only included as a part of CDPv2. This information
is noted in the table.
The
show cdp neighbors
command displays CDP information collected by a device about
its neighbors. It can be issued at a console connected to a Cisco network device.
Demonstrate the
show cdp neighbors
command and the
show cdp neighbors
detail
command. Note that much of the information outlined in the table can only be seen if
the
detail
option is utilized. This command variation is seen in subsequent RIOs. Some
information is only displayed with CDPv2, which is implemented with IOS version 12.0(3)T.
Demonstrate how the
show cdp neighbors
command and its variations can be consoled
into a router that is connected to another router or a switch to show students the output.
The
show cdp neighbors
command allows students to perform the associated Flash e-
Lab.
TLV Definition
Device-ID TLV
Identifies the device name in the form of a
character string
Address TLV
Contains a list of network address of both
receiving and transmitting devices
Port-ID TLV
Identifies the port on which the CDP packet is
sent
Capabilities TLV
Describes the functional capabilities of a device
in the form of a device type such as a switch
Version TLV
Contains information about the software release
version on which the device is running
Platform TLV
Describes the hardware platform name of the
device
IP Network Prefix TLV CDPv2
Contains a list of network prefixes to which the
sending device can forward IP packets. This
information is in the form of the interface
protocol and port number such as Eth 0/1
VTP Management Domain TLV
CDPv2
Advertises the configured VTP management
domain name string of a network and is used by
network operators to verify VTP domain
configuration in adjacent network nodes
Native VLAN TLV CDPv2
Indicates the assumed VLAN for untagged
packets on each interface and is implemented
only for interfaces the support the IEEE 802.1Q
protocol
Full or Half Duplex TLV
Indicates the status duplex configuration of a
CDP broadcast interface and is used by network
administrators to diagnose connectivity
problems between adjacent network devices