Reverse IP

Reverse lookup is needed for several uses. To check what is the reverse of an IP address, one can issue:

        dig -t PTR +short 99.123.204.41.in-addr.arpa.

Easily reverse an IP

Using "awk", reversing an IP address can be done with

        $ echo "41.204.123.99" | awk -F "." '{for (i=NF;i>=1;i--) printf $i"."; print "in-addr.arpa."}'
Or putting this in a simple SHELL script (i.e "flip-ip.sh"): 
        #!/bin/bash
        echo $1 | awk -F "." '{for (i=NF;i>=1;i--) printf $i"."; print "in-addr.arpa."}'
and calling it: 
        $ ./flip-ip.sh  41.204.123.99
Used in one line with "dig": 
        $ dig -t PTR +short $(flip-ip.sh  41.204.123.99)