The notation 18.104.22.168/24 is commonly used in describing IP address ranges. It means “start with the address 22.214.171.124 and allow the right-most 8 bits to vary.” The 8 is calculated by using 32 bits (the maximum for an IP address) minus 24 (the size specified after the “/”). So 126.96.36.199/24 means all addresses from 188.8.131.52 to 184.108.40.206.
We’ve elected to use the same IP address ranges and domain name throughout this book. For Internet-routable IP address ranges, we’re using the blocks 220.127.116.11-18.104.22.168 (or 22.214.171.124/8) and 126.96.36.199-188.8.131.52 (184.108.40.206/8), which we subnet to suit our needs. These ranges were chosen because they are designated as Internet routable, but are reserved by the IANA and aren’t currently being used. We hope that using these ranges, rather than randomly picking some or choosing them from “active” registered networks, will makes examples and figures easier to understand while protecting the innocent. We found that this helped us maintain our own sanity while writing the book.
For internal networks, we use the IP ranges set aside in RFC 1918 for use on private networks. These ranges are 10.0.0.0-10.255.255.255 (or 10.0.0.0/8), 172.16.0.0-172.31.255.255 (or 172.16.0.0/12), and 192.168.0.0-192.168.255.255 (or 192.168.0.0/16). We also subnet these as we deem necessary for an example.
The domain name we use for our examples is ora-vpn.com. Within this domain, however, we don’t have a hostname convention, because we typically create a hostname to match whatever solution we are writing about in a given chapter.