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Tools for identifying IP addresses

A site member asks our networking expert what tools are available to identify IP addresses on his customer's LAN.

What tools are available to identify IP addresses on my customer's LAN?

The best way to approach this problem is to query each possible IP address on the LAN to see if a host responds. There are several utilities that will do this for you. First, of course, is the venerable ping utility. Most ping implementations can query only a single host at a time, so a completely automated search would require calling ping from a script. Fortunately, there are more convenient solutions. The fping utility can send a ping to a range of addresses or to a whole subnetwork with a single invocation. For example, to ping every address on the 192.168.3.X subnet, we would invoke fping as

fping -g
fping -g

Another, more flexible, tool is nmap. Because it is intended primarily as a security testing tool, nmap is adept at finding hosts on a network. To query the same subnet as in the fping example, we would invoke nmap as

nmap –sP

All of the utilities that we discussed above are open source and available for Unix/Linux, MAC, and Windows. Because many system administrators configure network firewalls to filter ICMP ping packets, it is best to run these tools from a host on the LAN you are testing.

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