Information Technology Reference
In-Depth Information
Source and destination IP addresses
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Source and destination interface identifiers
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TCP/UDP source and destination port numbers
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Number of bytes and packets per flow
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Source and destination autonomous system numbers
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IP type of service (ToS)
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CDP
Cisco Discovery Protocol (CDP) is a Cisco-proprietary protocol that can be used to dis-
cover only Cisco network devices. CDP is media and protocol independent, so it works
over Ethernet, Frame Relay, ATM, and other media. The requirement is that the media sup-
port Subnetwork Access Protocol (SNAP) encapsulation. CDP runs at the data link layer
of the OSI model. CDP uses hello messages; packets are exchanged between neighbors,
but CDP information is not forwarded. In addition to routers and switches, IP phones and
Cisco Unified Communication Manager (CUCM) servers also advertise CDP information.
Key
To p i c
Being protocol and media independent is CDP's biggest advantage over other network
management technologies. CDP provides key information about neighbors, including plat-
for m s, c apabilit ie s, and IP addre s s e s, which is s ig nific ant for net work dis cover y. It is u s e -
ful when SNMP community strings are unknown when performing a network discovery.
When displaying CDP neighbors, you can obtain the following information:
Local interface:
Local interface that is connected to the discovered neighbor
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Device ID:
Name of the neighbor device and MAC address or serial number
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Device IP address:
IP address of the neighbor
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Hold time:
How long (seconds) to hold the neighbor information
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Device capabilities:
Ty pe of dev ice discovered: router, sw itch, transparent bridge,
host, IGMP, repeater
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Version:
IOS or switch OS version
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Platform:
Router or switch model number
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Port ID:
Interface of the neighboring device
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Network management devices can obtain CDP information for data gathering. CDP
should be disabled on untrusted interfaces, such as those that face the Internet, third-
party networks, or other secure networks. CDP works only on Cisco devices.
Note:
Disable CDP on interfaces for which you do not want devices to be discovered,
such as Internet connections.
