Networking - ASN (Autonomous System Number) - Determine which IPs actually fall into an ASN

Taking AS41264, which is a Google ASN, as an example:

whois -h whois.radb.net -- '-i origin AS41264' | grep ^route | grep -v route6 | cut -d" " -f7 | most

returns:

74.125.63.0/24
74.125.58.0/24
74.125.60.0/24
104.132.0.0/16
104.132.0.0/23
104.132.2.0/23
104.132.4.0/23
104.132.6.0/23
104.132.8.0/23
104.132.10.0/23
...

NOTE: The IP addresses within an ASN may change often, so if you do use this for firewalling then update the list regularly.

Note that other ASNs may also contain the same IP. So blocking any ASN that contains that IP will work.