Convert network->gateway mapping into DHCP 121 option

calculate-dhcp-route.py

# Convert network->gateway mapping into DHCP 121 option
# 
# conf.txt:
#
#    10.210.15.0/24 10.210.14.99
#    10.213.0.0/24 10.210.14.98
#    10.214.0.0/24 10.210.14.98
#    192.168.0.0/24 10.210.14.98
#    172.24.0.0/16 10.210.14.98
#
# usage:
#    python3 calculate-dhcp-route.py conf.txt

import argparse
import ipaddress

parser = argparse.ArgumentParser()
parser.add_argument('config')

args = parser.parse_args()
result = []
with open(args.config) as f:
    for l in f:
        i,g = l.strip().split(' ')
        net = ipaddress.IPv4Network(i)
        gw = ipaddress.IPv4Address(g)

        hm = net.hostmask.packed
        na = net.network_address.packed
        out = []
        include = False
        for i in range(3,-1,-1):
            if hm[i] != 255 or include:
                include = True
                out.append(na[i])
        out.append(net.prefixlen)
        out = list(reversed(out))
        for i in gw.packed:
            out.append(i)
        o = ':'.join([format(o, '02x') for o in out])
        print(net,gw,'=>', o)
        result.append(o)
print('dhcp 121 => ' + ':'.join(result))