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Cisco Discovery Protocol (CDP) is Cisco’s proprietary, data link layer protocol of the OSI model. It is used with most Cisco networking equipment, including routers, bridges, access servers and switches. CDP shares information about connected network devices such as interfaces used by routers, IP addresses and the operating system version. CDP can also allow two systems that are operating on different network layer protocols to learn about each other.
In February 2006, Hewlett-Packard removed support for transmitting CDP information from their products. CDP support has also been replaced with IEEE 802.1AB Link Layer Discovery Protocol, a standard similar to CDP and implemented by numerous vendors.
CDP shares different kinds of information called announcements. In addition to the version of the OS and all IP addresses from every protocol that are configured on the port where the CDP frame (data) is sent, CDP shares the following information:
Details of this information can be expanded with the use of the type-length-value data frame format, which is also called data packet format.