[dns-wg] Question about use of cname in Google's services

Anurag,

At 2016-06-04 02:52:46 +0530
Anurag Bhatia <me at anuragbhatia.com> wrote:

> Someone asked me question on why google uses cname for their services
> anyways? I mean I get it that for Google Apps customers it makes sense to
> have mail.domain.com pointed to a cname rather then A record to a host
> which may die.
> 
> But why for their own services? Like e.g "mail.google.com" is cname to
> googlemail.l.google.com. and googlemail.l.google.com. eventually returns A
> record. This adds up one extra step in resolution and I wonder why Google
> does it this way? What advantage they get ? or What advantage they miss if
> they simply return record which I am getting for googlemail.l.google.com.
> directly as A record for mail.google.com ?

I guess that this is a CDN trick, to give different answers based on
the resolver's originating IP address (or client-subnet EDNS0
information, if available).

In Beijing I get this:

$ host mail.google.com
mail.google.com is an alias for googlemail.l.google.com.
googlemail.l.google.com is an alias for mail-china.l.google.com.
mail-china.l.google.com has address 74.125.203.19
mail-china.l.google.com has address 74.125.203.18
mail-china.l.google.com has address 74.125.203.17
mail-china.l.google.com has address 74.125.203.83
mail-china.l.google.com has IPv6 address 2404:6800:4005:802::2005

The CNAME chain can send users to servers closer to where they are, and
allows operators to redirect traffic to less-busy servers or even take
sites offline easily.

Cheers,

--
Shane
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