ip – Ryan Schulze

How to break down CIDR subnets in Bash

December 11, 2012September 27, 2014Ryanbash, cidr, ip, math, subnet

I was playing around with subnets in bash recently and needed an elegant/easy way to split up a subnet into smaller subnets. First I used 2 functions I found on stackoverflow.com to convert an IP addresse to and from an integer. After that it was just a bit of math in bash to split up any networks too big.
Any network larger than $maxSubnet gets split up.
Here the useful code:

#!/bin/bash
. functions_ip2long.sh

input='10.1.4.0/22 10.2.2.0/24 10.3.3.128/25'
output=
maxSubnet=24

for pair in ${input}
do
  # split up the network and netmask
  network=${pair%/*}
  netmask=${pair#*/}
  if [[ ${netmask} -ge ${maxSubnet} ]]
  then # network is smaller than max. size. add it to the array
    output="${output} ${network}/${netmask}"
  else # network is too big. split it up into smaller chunks and add them to the array
    for i in $(seq 0 $(( $(( 2 ** (${maxSubnet} - ${netmask}) )) - 1 )) )
    do # convert network to long integer, add n * ${maxSubnet} and then convert back to string
      output="${output} $( INET_NTOA $(( $( INET_ATON ${network} ) + $(( 2 ** ( 32 - ${maxSubnet} ) * ${i} )) )) )/${maxSubnet}"
    done
  fi
done

echo ${output}|tr ' ' '\n'

#!/bin/bash

. functions_ip2long.sh

input='10.1.4.0/22 10.2.2.0/24 10.3.3.128/25'

output=

maxSubnet=24

for pair in ${input}

# split up the network and netmask

network=${pair%/*}

netmask=${pair#*/}

if [[ ${netmask} -ge ${maxSubnet} ]]

then # network is smaller than max. size. add it to the array

output="${output} ${network}/${netmask}"

else # network is too big. split it up into smaller chunks and add them to the array

for i in $(seq 0 $(( $(( 2 ** (${maxSubnet} - ${netmask}) )) - 1 )) )

do # convert network to long integer, add n * ${maxSubnet} and then convert back to string

output="${output} $( INET_NTOA $(( $( INET_ATON ${network} ) + $(( 2 ** ( 32 - ${maxSubnet} ) * ${i} )) )) )/${maxSubnet}"

done

echo ${output}|tr ' ' '\n'

Output of script:

10.1.4.0/24
10.1.5.0/24
10.1.6.0/24
10.1.7.0/24
10.2.2.0/24
10.3.3.128/25

10.1.4.0/24

10.1.5.0/24

10.1.6.0/24

10.1.7.0/24

10.2.2.0/24

10.3.3.128/25

MySQL selecting IPs via CIDR

February 23, 2011December 15, 2017Ryancidr, inet_aton, inet_ntoa, ip, myysql, network

Quick little snippet here for selecting IPs from a database based off a CIDR subnet. First off a table structure with some test data:

mysql> desc tmp;
+-------+------------------+
| Field |     Type         |
+-------+------------------+
| ip1   | int(12) unsigned |  
| ip2   | varchar(15)      |
+-------+------------------+

mysql> select * from tmp;
+------------+-----------------+
| ip1        |             ip2 |
+------------+-----------------+
| 16909060   | 1.2.3.4         |
| 167904004  | 10.2.3.4        |
| 2915086080 | 173.192.175.0   |
| 2915086100 | 173.192.175.20  |
| 2915086335 | 173.192.175.255 |
+------------+-----------------+

mysql> desc tmp;

+-------+------------------+

| Field | Type |

+-------+------------------+

| ip1 | int(12) unsigned |

| ip2 | varchar(15) |

+-------+------------------+

mysql> select * from tmp;

+------------+-----------------+

| ip1 | ip2 |

+------------+-----------------+

| 16909060 | 1.2.3.4 |

| 167904004 | 10.2.3.4 |

| 2915086080 | 173.192.175.0 |

| 2915086100 | 173.192.175.20 |

| 2915086335 | 173.192.175.255 |

+------------+-----------------+

Now let’s say we want all IPs from the subnet 173.192.175.16/28, using a simple 173.192.175.% would provide false results since you don’t want the whole /24.

If your IP is stored as an unsigned int (good for you) than you can use this snippet to search for matching IPs:

select inet_ntoa(ip1) as ip1,ip2 from tmp where (ip1 & power(2, 32) - power(2, (32 - 28))) = inet_aton('173.192.175.16');

1	select inet_ntoa(ip1) as ip1,ip2 from tmp where (ip1 & power(2, 32) - power(2, (32 - 28))) = inet_aton('173.192.175.16');

If your IP is stored as a varchar (for whatever reason), the only difference is a inet_aton() around the IP field.

select inet_ntoa(ip1) as ip1,ip2 from tmp where (inet_aton(ip2) & power(2, 32) - power(2, (32 - 28))) = inet_aton('173.192.175.16');

1	select inet_ntoa(ip1) as ip1,ip2 from tmp where (inet_aton(ip2) & power(2, 32) - power(2, (32 - 28))) = inet_aton('173.192.175.16');

No matter which one you use, the result will be:

+----------------+----------------+
| ip1            |         ip2    |
+----------------+----------------+
| 173.192.175.20 | 173.192.175.20 |
+----------------+----------------+

+----------------+----------------+

| ip1 | ip2 |

+----------------+----------------+

| 173.192.175.20 | 173.192.175.20 |

+----------------+----------------+