A simple python script converts a Classless Inter-Domain Routing (CIDR)-formatted IP address into an IP range and netmask.

subnet.py

#!/usr/bin/env python
# python subnet.py 200.100.33.65/26
# from: curl -O https://gist.githubusercontent.com/RichardBronosky/1aed6606b1283277e7ff9eaa18097e78/raw/subnet.py

import sys

# Get address string and CIDR string from command line
(addrString, cidrString) = sys.argv[1].split('/')

# Split address into octets and turn CIDR into int
addr = addrString.split('.')
cidr = int(cidrString)

# Initialize the netmask and calculate based on CIDR mask
mask = [0, 0, 0, 0]
for i in range(cidr):
	mask[i/8] = mask[i/8] + (1 << (7 - i % 8))

# Initialize net and binary and netmask with addr to get network
net = []
for i in range(4):
	net.append(int(addr[i]) & mask[i])

# Duplicate net into broad array, gather host bits, and generate broadcast
broad = list(net)
brange = 32 - cidr
for i in range(brange):
	broad[3 - i/8] = broad[3 - i/8] + (1 << (i % 8))

# Locate usable IPs
hosts = {"first":list(net), "last":list(broad)}
hosts["first"][3] += 4 # Normally +1 but AWS uses the first 4 IPs http://j.mp/2eeNF6f
hosts["last"][3] -= 1

# Count the difference between first and last host IPs
hosts["count"] = 0
for i in range(4):
    hosts["count"] += (hosts["last"][i] - hosts["first"][i]) * 2**(8*(3-i))

# Print information, mapping integer lists to strings for easy printing
if len(sys.argv) > 2:
    print ""
    print "Name:       ", sys.argv[2]
print "CIDR:       ", addrString, "/", cidr
print "Address:    ", addrString
print "Netmask:    ", ".".join(map(str, mask))
print "Network:    ", ".".join(map(str, net))
print "Broadcast:  ", ".".join(map(str, broad))
print "Host Range: ", ".".join(map(str, hosts["first"])),"-",".".join(map(str, hosts["last"]))
print "Host Count: ", hosts["count"]