- [Instructor] The proprietary cisco discovery protocol,
when enabled, discover some standard information
about neighboring cisco devices.
CDP messages are sent out active interfaces,
regularly sharing the following information.
Device identifier, which is the host name,
address list, which is the network and MAC addresses,
port identifier, which is the interface name
that is sending the message,
capabilities list, which is basic info
on the device type, say router, switch, phone, etc.
Platform displays the model
and level of operating system on the device.
CDP serves a couple of roles in the network.
One, is information to devices,
and the other is information to engineers.
For example, cisco IP phones,
use CDP to determine what the voice
and data VLAN ID's are.
Supplying information to engineers
is simply done with show CDP neighbors.
If more information is desired,
the engineer cornishway shows CDP neighbor detail.
This command will show the full set of information learned.
This can be particularly useful
when exploring a new network.
When determining paths as show CDP neighbor detail,
will give the connected interface
between the switch I'm on and the next.
I can continue the process
until I have the complete network mapped.
Depending on the devices capabilities,
CDP can be enabled or disabled per interface or globally.
CDP is enabled per interface with CDP enable.
If CDP needs to be disabled on a particular interface,
then they know CDP command can be issued.
To enable CDP globally, the CDP run command is issued
and to disable it globally,
the no form is used, no CDP run.
CDP was developed before there was a standard
for this type of communication,
as this is the case for many things.
The standards based link layer discovery protocol
can now be used for similar information sharing
among many vendors equipment.
Not only does LLDP share virtually the same information,
it's show commands are identical,
say for swapping LLDP for CDP.
LLDP is run globally with LLDP run.
It's enabled on an interface with LLDP transmit
to send messages and LLDP receive to except messages.
LLDP has the ability to only send,
only receive, or do both.
CDP be has been a life saver over the years,
it allows me to map unknown network topologies
from thousands of miles away.