Layer 2 discovery protocols allow devices to learn about neighboring devices on a network. Two of the most commonly used protocols are Cisco Discovery Protocol (CDP) and Link Layer Discovery Protocol (LLDP). This blog post, part of the CCNA course series, will discuss the strengths and weaknesses of these protocols.
Overview of Layer 2 Discovery Protocols:
Layer 2 discovery protocols, such as CDP and LLDP, operate at Layer 2 and share information with neighboring devices. They do not use IP addresses but can share Layer 3 information, such as IP addresses. This shared information includes host names, IP addresses, and device types. While these protocols can be considered a security risk, it is up to the network engineer/administrator to decide whether or not to use them.
CDP (Cisco Discovery Protocol):
CDP is a Cisco proprietary protocol that is included in most Cisco devices. It provides detailed information about Cisco devices on the network, including the device type, version of IOS, and interfaces. However, CDP only works with Cisco devices and is not compatible with devices from other vendors.
The salient features of CDP include:
- It is a Cisco proprietary protocol.
- It is enabled on Cisco devices by default.
- CDP messages are sent once every 60 seconds by default.
- CDP hold time is 180 seconds by default.
- CDPv1 is not in use anymore.
- It can be used for troubleshooting and monitoring the network.
LLDP (Link Layer Discovery Protocol):
LLDP is an industry-standard protocol that can be used with any type of device. While it is not as detailed as CDP, it can still provide useful information about devices on the network. LLDP is relatively easy to configure and is compatible with devices from different vendors.
The important features of LLDP include:
- It is an industry-standard protocol (IEEE 802.1AB).
- It is usually disabled on Cisco devices by default and needs to be enabled by the user.
- LLDP messages are sent once every 30 seconds by default.
- LLDP hold time is 120 seconds by default.
- It can be used for troubleshooting and monitoring the network.
Conclusion:
Both CDP and LLDP have their own strengths and weaknesses. The choice of protocol depends on the specific needs of the network. While CDP provides more detailed information about Cisco devices, LLDP is an industry-standard protocol that is compatible with devices from different vendors. Ultimately, the decision of which protocol to use rests with the network engineer/administrator.
