I am using curl to test an HTTP channel, connecting to Google.com. I am wondering as sometime I see the connection is toward zrh11s03-in-f4.1e100.net. This resolves to an IP that is effectively google.com, but I am wondering why and what is such domain name?



Here reverse DNS is being used to describe the machine having this address, not the services provided by it.

It is important that there isn't a 1:1 correspondence between websites and servers. The website "google.com" isn't handled by a single server, it is hosted on hundreds of systems, each of which has its own unique name to allow the admins to identify it – and at the same time, those machines host more websites than just the single "google.com" so it wouldn't make sense for their reverse DNS to point to just that single domain.

So instead of trying to put potentially inaccurate and rapidly changing information in rDNS, the operator just uses it to directly describe what sort of device the address has been assigned to. The hostname zrh11s03-in-f4 was chosen by Google's infrastructure team to describe where the specific machine is ("zrh" is likely Zurich, the rest probably indicate racks or ports or interfaces or something similar).

The overall domain 1e100.net is a Google-owned domain name. It is common for network operators to have several domain names, with the ones used for public-facing sites being kept separate from those used for internal infrastructure. They're managed by different teams with different purposes and rules, etc.

Often the infrastructure domains are named after something which alludes to the company's name without actually mentioning any trademarks (for example, the network's AS number is a very common choice and you'll see a lot of asXXXXX.net in traceroutes).

The number 1×10100, written as 1e100 in most programming languages, is called a googol.

  • thanks. What I do not completely understand is "Here reverse DNS is being used to describe the machine having this address, not the services provided by it.". Also, why is it a reverse DNS? – toto' Jan 26 at 15:36
  • Also, the address zrh11s03-in-f4.1e100.net in a Web Browser gives a "Page Not Found" error. I thought it would give the Google.com page instead. – toto' Jan 26 at 15:40
  • 4
    1) It's called "reverse DNS" because you're translating an IP address to a domain name, which is the reverse of how DNS is typically used. 2) See again "those machines host more websites than just the single google.com". If you make an HTTP request with one domain name they'll give you one website; if you make a request with another domain name they'll respond with another website. This is how practically all webservers work. (Also known as 'virtual hosting' or 'shared hosting'.) – user1686 Jan 26 at 15:44
  • 2
    "hundreds of systems" is the understatement of the decade :-) Probably hundreds of thousands, possibly more. – jcaron Jan 26 at 23:50

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.