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

Hi Shane



Sure, they route googlemail.l.google.com. to nearest datacenter but when
prevents them from doing same with mail.google.com instead?

They return Geographically closer A record for googlemail.l.google.com. but
why not for mail.google.com itself?




Thanks.

On Sat, Jun 4, 2016 at 10:31 AM, Shane Kerr <shane at time-travellers.org>
wrote:

> 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
>



-- 


Anurag Bhatia
anuragbhatia.com
-------------- next part --------------
An HTML attachment was scrubbed...
URL: </ripe/mail/archives/dns-wg/attachments/20160604/58ddfe62/attachment.html>