The following IP address ranges are known to be used by Facebook:

66.220.144.0 – 66.220.159.255
69.63.176.0 – 69.63.191.255
69.171.224.0 – 69.171.255.255
204.15.20.0 – 204.15.23.255

Additional IP ranges which may be assigned to Facebook:

65.201.208.24/29
65.204.104.128/28
66.92.180.48/28
66.93.78.176/29
66.199.37.136/29
67.200.105.48/30
74.119.76.0/22
173.252.64.0/18

Updated IP ranges can always be retrieved with:

whois -h whois.radb.net ‘!gAS32934’