What are these Google IPs hammering on my DNS server?

["John Levine" <johnl () iecc com>]

At contacts.abuse.net, I have a little stunt DNS server that provides domain contact info, e.g.:

$ host -t txt comcast.net.contacts.abuse.net
comcast.net.contacts.abuse.net descriptive text "abuse () comcast net"

$ host -t hinfo comcast.net.contacts.abuse.net
comcast.net.contacts.abuse.net host information "lookup" "comcast.net"

Every once in a while someone decides to look up every domain in the
world and DoS'es it until I update my packet filters. This week it's
been this set of IPs that belong to Google. I don't think they're
8.8.8.8. Any idea what they are? Random Google Cloud customers? A
secret DNS mapping project?

 172.253.1.133 
 172.253.206.36 
 172.253.1.130 
 172.253.206.37 
 172.253.13.196 
 172.253.255.36 
 172.253.13.197 
 172.253.1.131 
 172.253.255.35 
 172.253.255.37 
 172.253.1.132 
 172.253.13.193 
 172.253.1.129 
 172.253.255.33 
 172.253.206.35 
 172.253.255.34 
 172.253.206.33 
 172.253.206.34 
 172.253.13.194 
 172.253.13.195 
 172.71.125.63 
 172.71.117.60 
 172.71.133.51 

R's,
John