How to find google IP address range

I wanted to track google IP range in one of the investigation. So, I did this:

[admin@psj ~]$ nslookup -type=txt _spf.google.com 8.8.8.8
Server:        8.8.8.8
Address:    8.8.8.8#53

Non-authoritative answer:
_spf.google.com    text = "v=spf1 include:_netblocks.google.com include:_netblocks2.google.com include:_netblocks3.google.com ~all"

Authoritative answers can be found from:
google.com    nameserver = ns2.google.com.
google.com    nameserver = ns3.google.com.
google.com    nameserver = ns1.google.com.
google.com    nameserver = ns4.google.com.
ns2.google.com    internet address = 216.239.34.10
ns3.google.com    internet address = 216.239.36.10
ns1.google.com    internet address = 216.239.32.10
ns4.google.com    internet address = 216.239.38.10

Run a nslookup for each one:
$ nslookup -q=TXT _netblocks.google.com 8.8.8.8
$ nslookup -q=TXT _netblocks2.google.com 8.8.8.8


[admin@psj ~]$ nslookup -type=txt _netblocks.google.com
Server:        8.8.8.8
Address:    8.8.8.8#53

Non-authoritative answer:
_netblocks.google.com    text = "v=spf1 ip4:64.18.0.0/20 ip4:64.233.160.0/19 ip4:66.102.0.0/20 ip4:66.249.80.0/20 ip4:72.14.192.0/18 ip4:74.125.0.0/16 ip4:108.177.8.0/21 ip4:173.194.0.0/16 ip4:207.126.144.0/20 ip4:209.85.128.0/17 ip4:216.58.192.0/19 ip4:216.239.32.0/19 ~all"

Authoritative answers can be found from:
google.com    nameserver = ns2.google.com.
google.com    nameserver = ns3.google.com.
google.com    nameserver = ns4.google.com.
google.com    nameserver = ns1.google.com.
ns2.google.com    internet address = 216.239.34.10
ns3.google.com    internet address = 216.239.36.10
ns1.google.com    internet address = 216.239.32.10
ns4.google.com    internet address = 216.239.38.10

You can also use whois query to find out network blocks assigned to google.
$ whois 74.125.127.108