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 <[email protected]> wrote: > Anurag, > > At 2016-06-04 02:52:46 +0530 > Anurag Bhatia <[email protected]> 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
