> For the complete documentation index, see [llms.txt](https://citizenseven.gitbook.io/ccna-prep/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://citizenseven.gitbook.io/ccna-prep/cdp-and-lldp.md). # CDP & LLDP Layer 2 discovery protocols (CDP and LLDP) share information with and discover information about neighbouring devices. The shared information includes hostname, IP address, device type, etc. ### CDP **CDP** (Cisco Discovery Protocol) is a Cisco proprietary protocol which is enabled on all Cisco devices by default. The default version is CDPv2. CDP messages are periodically sent to multicast MAC address `0100.0ccc.cccc`. When a device receives a CDP message, it processes and discards the message without forwarding it to other devices. By default, CDP messages are sent every 60 seconds. The default hold time is 180 seconds. #### Verification To see CDP configurations, enter the `show cdp` command, for CDP traffic - `show cdp traffic`, and for CDP information about each interface - `show cdp interface`. To see the CDP neighbours, enter the command `show cdp neighbors` or `show cdp neighbors detail`, for the specified neighbour - `show cdp entry` followed by the hostname.
show cdp neighbors command
#### Configuration * Enable/disable CDP globally - `cdp run`/`no cdp run`. * Enable/disable CDP on a specific interface - `cdp enable`/`no cdp enable`. * Configure the CDP timer - `cdp timer` followed by the value in seconds. * Configure the CDP hold time - `cdp holdtime` followed by the value in seconds. * Enable/disable CDPv2 - `cdp advertise-v2`/`no cdp advertise-v2`. ### LLDP **LLDP** (Link Layer Discovery Protocol) is an industry-standard protocol (IEEE 802.1ab). It is usually disabled on Cisco devices by default. A device can run CDP and LLDP at the same time. LLDP messages are multicast to MAC address `0180.c200.000e`. By default, LLDP messages are sent every 30 seconds and holdtime is 120 seconds. It also has an additional timer - reinitialization delay. When LLDP is enabled, this timer delays the actual initialization of LLDP. It is 2 seconds by default. #### Verification The commands and outputs are very similar to CDP. * For basic information - `show lldp`. * For LLDP stats - `show lldp traffic`. * For LLDP-enabled interfaces - `show lldp interface`. * For LLDP neighbours - `show lldp neighbors` or `show lldp neighbors detail`, for the specified neighbour - `show lldp entry` followed by the hostname.
show lldp neighbors command
#### Configuration * Enable LLDP globally - `lldp run`. * Enable LLDP to transmit on a specific interface - `lldp transmit`. * Enable LLDP to receive on a specific interface - `lldp receive`. * Configure the LLDP timer - `lldp timer` followed by the value in seconds. * Configure the LLDP hold time - `lldp holdtime` followed by the value in seconds. * Configure the LLDP reinit timer - `lldp reinit` followed by the value in seconds. {% file src="/files/w8GrENEholDjXY9UNvXG" %} {% file src="/files/Yb6eLKZaaonE10HTJPJs" %} {% embed url="" %} --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter: ``` GET https://citizenseven.gitbook.io/ccna-prep/cdp-and-lldp.md?ask=&goal= ``` `ask` is the immediate question: it should be specific, self-contained, and written in natural language. `goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.