Step 1: Find the network to scan

core~> whois -h whois.arin.net n playboy
[...]
OrgName:    Playboy 
OrgID:      PLAYBO
Address:    680 N. Lake Shore Drive
City:       Chicago
StateProv:  IL
PostalCode: 60611
Country:    US

NetRange:   216.163.128.0 - 216.163.143.255 
CIDR:       216.163.128.0/20 [...]