Added IPv4 Subnet Cheatsheet in Appendix B

Author: gnebbia

README.md

@@ -1436,10 +1436,39 @@ vulnerabilities our system is affected we can do:
  sudo nmap --script "vuln and not (dos or exploit or intrusive)" www.22hits.com 
  # this is a safer version of the last command, since it won't execute exploits
 ```
-## Appendix
+## Appendix A: Nmap Flags Cheatsheet
 
 Here we'll put an nmap cheatsheet, which wraps up all the Network 
 Mapping phases with relative commands, this can be useful to us 
 for many situations.
 
 ![alt text](img/nmap_cheatsheet.png "nmap cheatsheet")
+
+
+## Appendix B: IPv4 Subnet Cheatsheet
+
+/31 255.255.255.254 1 Host
+/30 255.255.255.252 2 Hosts
+/29 255.255.255.249 6 Hosts
+/28 255.255.255.240 14 Hosts
+/27 255.255.255.224 30 Hosts
+/26 255.255.255.192 62 Hosts
+/25 255.255.255.128 126 Hosts
+/24 255.255.255.0 254 Hosts
+/23 255.255.254.0 512 Host
+/22 255.255.252.0 1022 Hosts 
+/21 255.255.248.0 2046 Hosts
+/20 255.255.240.0 4094 Hosts
+/19 255.255.224.0 8190 Hosts 
+/18 255.255.192.0 16382 Hosts
+/17 255.255.128.0 32766 Hosts
+/16 255.255.0.0 65534 Hosts
+/15 255.254.0.0 131070 Hosts
+/14 255.252.0.0 262142 Hosts 
+/13 255.248.0.0 524286 Hosts
+/12 255.240.0.0 1048674 Hosts
+/11 255.224.0.0 2097150 Hosts
+/10 255.192.0.0 4194302 Hosts 
+/9 255.128.0.0 8388606 Hosts 
+/8 255.0.0.0 16777214 Hosts
+