Check if IP Belongs to a CIDR

Question

We have a list of CIDR's

1.10.10.0/24
5.154.0.0/16
5.181.219.0/24
23.90.68.0/24
31.40.214.0/24

I want to check if a IP for example : 23.90.68.56 belongs to any of the above CIDR's. If yes then we get the output of that CIDR.

According the above example the output should be 23.90.68.0/24

I tried using grepcidr but I do not know how can we output that specific CIDR's

I am creating a bash script for this but can someone help me with this output thing? I tried searching the web but couldn't get anything relevant

[This two-part answer](https://networkengineering.stackexchange.com/a/53994/8499) has a section that detail exactly how to see if an address belongs to a network (is in the same network as the network address). You mask both the network and target addresses with the network mask, and if the results are equal, then they are the same network. — Ron Maupin, Jan 20 '23 at 20:42
You can do this using `nmap`. Long-winded command line is `for net in 1.10.10.0/24 5.154.0.0/16 5.181.219.0/24 23.90.68.0/24 31.40.214.0/24; do nmap -sL -n $net | grep -q 23.90.68.56 && echo $net; done`. Easily changed to a script with parameters. — doneal24, Jan 20 '23 at 20:45

doneal24 · Answer 1 · 2023-01-20T21:17:19.063

0

A possible shell script:

#!/bin/bash

ip=$1
shift; shift

for net in "$@"
do
    nmap -sL -n $net | grep -q $ip && echo $net
done

If you need the list of cidrs in a file use ./scriptname ip_to_be_checked $(cat filename). Possibly a useless use of cat.

./cidr.sh 23.90.68.56 $(cat cidrs.txt)

edited Jan 20 '23 at 21:17

answered Jan 20 '23 at 21:06

doneal24

851
6
14

@ph3ro If this works for you, please consider accepting the answer. It makes it more searchable plus increases my reputation :). – doneal24 Jan 20 '23 at 22:02
The second `shift` is excessive – it'll throw away $2 i.e. the first CIDR from the file. – user1686 Feb 03 '23 at 12:16

score 0 · Accepted Answer · answered Feb 03 '23 at 12:14

You probably have Python:

#!/usr/bin/env python3
import argparse
import ipaddress
import sys

parser = argparse.ArgumentParser()
parser.add_argument("address")
args = parser.parse_args()

addr = ipaddress.ip_address(args.address)

for line in sys.stdin:
    cidr = ipaddress.ip_network(line.strip())
    if addr in cidr:
        print(cidr)
        exit(0)

exit(1)

Walter Vehoeven · Answer 3 · 2023-02-03T13:26:29.830

in python, that would be:

import socket

def is_ip_in_cidr(ip, cidr):
    network, mask = cidr.split("/")
    mask = int(mask)
    ip_int = int.from_bytes(socket.inet_aton(ip), "big")
    network_int = int.from_bytes(socket.inet_aton(network), "big")
    network_mask = (0xFFFFFFFF << (32 - mask)) & 0xFFFFFFFF
    return (ip_int & network_mask) == network_int

# Test the function with a sample IP address and CIDR
ip = "192.168.0.5"
cidr = "192.168.0.0/24"

if is_ip_in_cidr(ip, cidr):
    print(f"{ip} is in {cidr}")
else:
    print(f"{ip} is NOT in {cidr}")

if you can use the list provided as a fixed set to test like so:

import socket

def is_ip_in_cidr(ip, cidrs):
    for cidr in cidrs:
        network, mask = cidr.split("/")
        mask = int(mask)
        ip_int = int.from_bytes(socket.inet_aton(ip), "big")
        network_int = int.from_bytes(socket.inet_aton(network), "big")
        network_mask = (0xFFFFFFFF << (32 - mask)) & 0xFFFFFFFF
        if (ip_int & network_mask) == network_int:
            return True
    return False

# Test the function with a sample IP address and list of CIDRs
ip = "192.168.0.5"
cidrs = ["1.10.10.0/24", "5.154.0.0/16", "5.181.219.0/24", "23.90.68.0/24", "31.40.214.0/24"]

if is_ip_in_cidr(ip, cidrs):
    print(f"{ip} is in one of {cidrs}")
else:
    print(f"{ip} is NOT in any of {cidrs}")

in bash

#!/bin/bash

function is_ip_in_cidr {
  local ip=$1
  local cidr=$2
  local network=$(echo $cidr | cut -d/ -f1)
  local mask=$(echo $cidr | cut -d/ -f2)
  local network_dec=$(echo $network | awk -F. '{printf("%d\n", ($1 * 256 + $2) * 256 + $3)}')
  local ip_dec=$(echo $ip | awk -F. '{printf("%d\n", ($1 * 256 + $2) * 256 + $3)}')
  local mask_dec=$((0xffffffff << (32 - $mask)))
  if [[ $((ip_dec & mask_dec)) -eq $((network_dec & mask_dec)) ]]; then
    echo "true"
  else
    echo "false"
  fi
}

# Test the function with a sample IP address and CIDR
ip="192.168.0.5"
cidr="192.168.0.0/24"

if $(is_ip_in_cidr $ip $cidr); then
  echo "$ip is in $cidr"
else
  echo "$ip is NOT in $cidr"
fi

Check if IP Belongs to a CIDR

3 Answers3