Reserved IPv4 Addresses
I got about halfway through typing this entry tonight, and it occurred to me to check Wikipedia. Lo and behold, a colorful grid laying out all sorts of info!
http://en.wikipedia.org/wiki/Reserved_IP_addresses
There are 16 total reserved networks, and 15 of them are covered in the excellent RFC 5735. The sixteenth address block, 100.64.0.0/10, is a newcomer. RFC 6598 was written in April 2012. The address space is intended for Carrier-Grade NAT (which is horrifying), but it does say “However, it may be used in a manner similar to RFC 1918 private address space”. Interesting!
Let’s break down that big Wikipedia table:
Private Network Address Ranges
IP Range # Addresses
10.0.0.0/8 16,777,216
172.16.0.0/12 1,048,576
192.168.0.0/16 65,536
Local Address Ranges
IP Range # Addresses Notes
0.0.0.0/8 16,777,216 For broadcast messages to current network
127.0.0.0/8 16,777,216 For loopback addresses to local host
169.254.0.0/16 65,536 For autoconfiguration between 2 hosts on a single link
Address Ranges for Documentation and Example Code
IP Range # Addresses
192.0.2.0/24 256
198.51.100.0/24 256
203.0.113.0/24 256
Special-Purpose Address Ranges
IP Range # Addresses Notes
100.64.0.0/10 4,194,304 For carrier-grade NAT, but may be used for private networks
192.0.0.0/29 8 For DS-Lite transition mechanism
192.88.99.0/24 256 For 6to4 anycast relays
198.18.0.0/15 131,072 For benchmark tests of routers
224.0.0.0/4 268,435,456 For multicast
240.0.0.0/4 268,435,455 For future use
255.255.255.255/32 1 For limited broadcast