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Find unused IPs on a given subnet

Terminal - Find unused IPs on a given subnet
nmap -sP <subnet>.* | egrep -o '[0-9]+\.[0-9]+\.[0-9]+\.[0-9]+' > results.txt ; for IP in {1..254} ; do echo "<subnet>.${IP}" ; done >> results.txt ; cat results.txt | sort -n -t . -k 1,1 -k 2,2 -k 3,3 -k 4,4 | uniq -u
2010-01-22 00:26:42
User: bortoelnino
Functions: cat echo egrep sort uniq
0
Find unused IPs on a given subnet

Alternatives

There is 1 alternative - vote for the best!

Terminal - Alternatives
nmap -T4 -sP 192.168.2.0/24 && egrep "00:00:00:00:00:00" /proc/net/arp
fping -r1 -g <subnet> 2> /dev/null | grep unreachable | cut -f1 -d' '

Know a better way?

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What others think

Here's a neat way to accomplish the same thing without using a results.txt file:

sort -n -t . -k 1,1 -k 2,2 -k 3,3 -k 4,4 <(nmap -sP 192.168.2.*|grep -Eo '([0-9]{1,3}\.){3}[0-9]{1,3}') <(printf "%s\n" 192.168.2.{1..254})|uniq -u

It works on ksh and bash and maybe other shells.

Comment by eightmillion 220 weeks and 6 days ago

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