Match an IP address or hostname against a cidr or list of cidrs, that can be used in .ssh/config

matchcidr

#!/usr/bin/env python3

import ipaddress
import socket
import sys
import getopt
import re


def check_cidr(cidr, ip):
    try:
        network = ipaddress.IPv4Network(cidr)
        ip_address = ipaddress.IPv4Address(ip)
        if ip_address in network:
            return True
        else:
            return False
    except ipaddress.AddressValueError:
        return False

def print_usage():
    usage = """Usage: matchcidr [-v] <ip_or_hostname> <cidr1> [cidr2 ...]
    
Options:
  -v             Enable verbose mode

Examples:
  matchcidr.py -v hostname 172.31.0.0/20
  matchcidr.py hostname 172.31.64.0/20
  matchcidr.py 172.31.74.141 172.31.0.0/20
  matchcidr.py 172.31.74.141 172.31.64.0/20
  
.ssh/config:
  Match exec "matchcidr %h 172.31.0.0/20 172.31.16.0/20"
    StrictHostKeyChecking no
    UserKnownHostsFile /dev/null
    LogLevel QUIET
"""

    print(usage)

def print_verbose(cidr, ip, result):
    print(f"Checking CIDR: {cidr} against IP: {ip} - Result: {result}")


def main():
    ip_or_hostname = ""
    cidrs = []
    verbose = False

    # Parse command-line options
    try:
        opts, args = getopt.getopt(sys.argv[1:], "v")
    except getopt.GetoptError as err:
        print(str(err))
        print_usage()
        sys.exit(2)

    for opt, _ in opts:
        if opt == "-v":
            verbose = True

    if len(args) < 2:
        print("Invalid arguments.")
        print_usage()
        sys.exit(2)

    ip_or_hostname = args[0]
    cidrs = args[1:]

    # Get the IP address if the argument is a hostname
    if not ip_or_hostname.replace(".", "").isdigit():
        try:
            ip_address = socket.gethostbyname(ip_or_hostname)
            ip_or_hostname = ip_address
        except socket.gaierror as err:
            print(f"Error: {str(err)}")
            sys.exit(1)

    # Iterate over each CIDR and check if the IP address matches
    for cidr in cidrs:
        cidr = cidr.strip(' ,')
        if check_cidr(cidr, ip_or_hostname):
            if verbose:
                print_verbose(cidr, ip_or_hostname, "Match")
            sys.exit(0)

    if verbose:
        for cidr in cidrs:
            print_verbose(cidr.strip(), ip_or_hostname, "No Match")

    sys.exit(1)


if __name__ == "__main__":
    main()