CDP and LLDP are protocols used to discover the neighboring devices of a router. CDP is used to discover Cisco devices, while LLDP is used to discover IEEE 802.1ab (LLDP) compatible devices.
What is CDP and LLDP?
CDP and LLDP are protocols that are used to discover information about other devices on the network. CDP and LLDP are enabled by default on most network devices.
CDP (Cisco Discovery Protocol) is used by Cisco routers to advertise their existence, as well as the type of router they are, to other neighboring devices. This is useful for determining whether there are any neighboring CDP-enabled devices on your LAN segment, which may not be physically connected but could still be able to communicate with each other over wireless channels or through network bridges/gateways if configured in such a way.
LLDP (Link Layer Discovery Protocol), also known as 802.1AB, allows switches and bridges to send out advertisements regarding their capabilities (eg: what ports they have available) and device vendor information (eg: Netgear vs Linksys). It’s important because you can use this information when looking through traffic logs later if something goes wrong with one of your networking devices – having that piece of knowledge makes it much easier!
How to use tcpdump to capture CDP or LLDP packet?
To capture CDP or LLDP packets using tcpdump, you can use the following command:
tcpdump -i <interface> -vvv -s 1500 -c 1 'ether[20:2] == 0x2000'
In this command, <interface> is the name of the network interface that you want to capture packets on. For example, if you want to capture packets on the eth0 interface, you would use the following command:
tcpdump -i eth0 -vvv -s 1500 -c 1 'ether[20:2] == 0x2000'
This command will capture the first CDP or LLDP packet that is received on the eth0 interface and print the packet details to the terminal. The -vvv option specifies that tcpdump should print detailed packet information, including the packet contents. The -s 1500 option specifies the maximum size of the packets to capture, and the -c 1 option specifies that only the first packet should be captured. The final 'ether[20:2] == 0x2000' option is a filter that specifies that only CDP or LLDP packets should be captured.
How to use tcpdump to filter CDP packet?
To capture CDP packets using tcpdump, you can use the following command:
tcpdump -i <interface> -vvv -s 1500 -c 1 'ether[20:2] == 0x2000'
In this command, <interface> is the name of the network interface that you want to capture packets on. For example, if you want to capture packets on the eth0 interface, you would use the following command:
tcpdump -i eth0 -vvv -s 1500 -c 1 'ether[20:2] == 0x2000'
This command will capture the first CDP packet that is received on the eth0 interface and print the packet details to the terminal. The -vvv option specifies that tcpdump should print detailed packet information, including the packet contents. The -s 1500 option specifies the maximum size of the packets to capture, and the -c 1 option specifies that only the first packet should be captured. The final 'ether[20:2] == 0x2000' option is a filter that specifies that only CDP packets should be captured.
How to use tcpdump to capture LLDP packet?
To capture LLDP packets using tcpdump, you can use the following command:
tcpdump -i <interface> -vvv -s 1500 -c 1 'ether[20:2] == 0x88cc'
In this command, <interface> is the name of the network interface that you want to capture packets on. For example, if you want to capture packets on the eth0 interface, you would use the following command:
tcpdump -i eth0 -vvv -s 1500 -c 1 'ether[20:2] == 0x88cc'
This command will capture the first LLDP packet that is received on the eth0 interface and print the packet details to the terminal. The -vvv option specifies that tcpdump should print detailed packet information, including the packet contents. The -s 1500 option specifies the maximum size of the packets to capture, and the -c 1 option specifies that only the first packet should be captured. The final 'ether[20:2] == 0x88cc' option is a filter that specifies that only LLDP packets should be captured.
There are several benefits to using Tcpdump for filtering CDP and LLDP packets:
1.Tcpdump is a powerful and flexible tool that allows you to capture and analyze network packets in real time. This can help you understand the behavior of your network and identify potential issues or problems.
2.Tcpdump allows you to filter packets based on various criteria, including the type of packet, the source and destination addresses, and the port numbers. This can help you focus on specific types of traffic and exclude irrelevant packets from the output.
3.Tcpdump provides detailed information about each packet, including the full packet contents and the headers of the various protocol layers. This can help you understand the structure and content of the packets, and can provide valuable information for troubleshooting and analysis.
4.Tcpdump is a command-line tool that can be easily integrated into scripts and automated processes. This allows you to automate the capture and analysis of network packets, and can help you monitor and manage your network more effectively.
Overall, using Tcpdump for filtering CDP and LLDP packets can provide valuable insights into your network and help you identify and resolve potential issues.