Why do Google Cloud Platform static IP addresses list Mountain View, CA in reverse lookup regardless of region assignment?

Solution 1:

It sounds like you are conflating three concepts:

• The domain registration for the googleusercontent.com reverse DNS
• The SWIP record for the subnet
• The routing decision to reach an IP

All three are independent. All GCE instance IP addresses have a reverse DNS entry that maps to xxx.xxx.xxx.xxx.bc.googleusercontent.com. This domain is under Google's control and therefore registered to the HQ in Mountain View.

The SWIP record / WHOIS entry denotes the administrative ownership of an IP address resp. its subnet. It's therefore also registered to the HQ in Mountain View.

Both of these do not reflect anything about physical location of the machine answering packets to an IP address nor the decisions on how packets are routed to the destination.

Google has a global network. Packets to a GCE instance will cross over to Google's network relatively close to the client. Since Google maintains a lot of peerings with ISPs worldwide, most of the time your packets will end up on Google's network directly from your ISP.

If you run a traceroute to your instance, you might see hops with airport codes in their reverse DNS names, especially when traversing peering points. The hops internal to Google usually do not hint any further at geographical location.

And finally, when the "proximity" or location of an IP address is discussed, most of the time the relevant metric is the latency or network distance to the host - not the geographical distance. (Although geographical distance sets a lower bound for latency as packets cannot go faster than the speed of light)