In this post, we are going to learn what is Cisco CDP protocol
The Cisco discovery protocol (also known as CDP) is a
network protocol that operates in layer 2 (Data Link Layer). It is
designed by Cisco to gather information about hardware, operating system
versions, protocols, and IP address of nearby, directly connected, neighboring
Cisco devices. It does all these things in order to simplify network
administration of cisco equipment, and as it is designed and developed by Cisco
and works on cisco devices only, so it is mainly a Cisco proprietary protocol.
This protocol makes it easier to manage Cisco devices by
identifying them, knowing how they're setup, and allowing systems to communicate
with each other and learn about one another using various network-layer
protocols.
All supported devices, including Cisco routers and switches,
have CDP enabled by default.
By default, messages received from a neighboring Cisco
device are not transmitted to any other devices. This implies that Cisco
Discovery Protocol (CDP) is only sent to Cisco devices that are physically
linked. The messages received from neighbor devices are stored in a table that
may be seen using the show CDP neighbors command on any Cisco device that
implements Cisco Discovery Protocol (CDP).
Whenever a Cisco device, such as a CDP-enabled router, gets
a CDP packet, it starts to create a table of adjacent devices. Once the devices
have been found, they transmit to each other a packet of updated data on a regular
basis. These CDP packets provide a variety of useful data about network
devices, including:
- Device type
- Hardware platform
- Hardware capabilities
- IOS version number
- Hostname
- The interface that generates CDP message
- IP address of the device
- Port ID
- Number of seconds for CDP advertisement is valid
the multicast destination address 01:00:0C:CC:CC:CC is used
by Cisco devices to deliver Cisco Discovery Protocol (CDP) messages. On
interfaces that implement Subnetwork Access Protocol (SNAP) headers, CDP
messages are transmitted every 60 seconds. Subnetwork Access Protocol (SNAP)
support isn't available on all data link layer media types. Ethernet, Token
Ring, Fiber Distributed Data Interface (FDDI), Point-to-Point Protocol (PPP), High-Level Data Link Control (HDLC), Asynchronous Transfer Mode (ATM), and Frame
Relay are among the media types supported by Cisco Discovery Protocol (CDP).