Technically a LAN Network would not respond to traditional pings, but there are several methods, which use pings, that find all of the devices on a LAN. A ping packet sent to the broadcast address of a LAN will often return responses from many of the devices connected to the LAN. You must understand IP addressing in order to calculate the broadcast address. Not all devices on a LAN will respond to a broadcast ping. Another method for finding the devices on a LAN is to use a ping scanning tool like nmap.
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Things you need
- namp software
Calculate the broadcast address on the LAN by calculating the highest available address in the range of addresses assigned to the LAN. If the mask for the network is /24 or 255.255.255.0, then the broadcast address is the address with 255 as the final number. For example, if your address is 192.168.1.14, the broadcast address for the network will be 192.168.1.255.
Type "ping -b 192.168.1.255" to ping the broadcast address. The "-b" parameter is required on some systems in order to allow a broadcast ping.
Interpret the output results. There will likely be multiple responses, one from each device on the network. Remember that not all devices will respond to broadcast pings and Windows has ping responses turned off by default when using the Windows Firewall.
Install the nmap program on your system if it is not already installed. Many Linux or Mac OS versions come with nmap installed by default. The program nmap is available as a free download from Insecure as shown in the references. This is the most common ping scanning tool although others are available, such as Ping Scan and Solar Winds Engineers Toolset.
Use the program nmap to do a ping scan of a series of address. Type "nmap -v -sP 192.168.1.0/24". This will sequentially ping all of the address in a particular network range.
Interpret the results. The program nmap will print out one line for every IP address in the range and specify whether the host appears to be up or down. Remember that Windows systems by default will appear down, unless exceptions have been allowed in the Windows Firewall.
Tips and warnings
- Use this technique frequently for networks that you administer. Internet crackers will be using it against you, so it's good to know what they know.
- Do not use this on any networks for which you are not the administrative authority unless you have written permission. These techniques can be considered invasive and subject to disciplinary action. In some jurisdictions they may be considered illegal.
- Do not attempt this at work unless you have written permission from management or are contracted as part of a security audit team. Without authorisation, these actions could result in workplace sanctions or dismissal.
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