nanog mailing list archives
Re: Question regarding anycasting in CDN setup
From: Anurag Bhatia <me () anuragbhatia com>
Date: Thu, 9 Feb 2012 01:21:17 +0530
Nice explanation! Thanks Mike. Appreciate it. On Thu, Feb 2, 2012 at 6:08 AM, Mike Jones <mike () mikejones in> wrote:
On 1 February 2012 20:25, Anurag Bhatia <me () anuragbhatia com> wrote: <snip>Now my question here is - why this setup and not simply using having a A record for googlehosted.l.googleusercontent.com. which comes from any anycasted IP address space? Why not anycasting at CDN itself rather then only at DNS layer?You are confusing anycasting with offering different results. I can have an anycast DNS setup where all my servers give the same response (example: most DNS providers), I can also have a single DNS server give 192.0.2.80 out to queries sourced from a US IP Address, 198.51.100.80 for queries sourced from a German IP Address and 203.0.113.80 to queries sourced from a Chinese address (djbdns has a module for this for example). I would guess that google probably have a highly customised algorithm which uses a combination of source IP and the node that your query arrived at as part of the process for deciding what answer to give you, along with dozens of other internal factors. Although I do sometimes wonder why they use CNAME chains in cases where the same servers are authoritative for the target name anyway. If you were wondering why they direct you to the unicast addresses for the local datacentre instead of just giving an anycast address which your nearest datacentre would answer, well their algorithm might decide that it wants to serve you content from the second closest datacentre because the closest one is near capacity, anycast can't do that. - Mike
-- Anurag Bhatia anuragbhatia.com or simply - http://[2001:470:26:78f::5] if you are on IPv6 connected network! Twitter: @anurag_bhatia <https://twitter.com/#!/anurag_bhatia> Linkedin: http://linkedin.anuragbhatia.com
Current thread:
- Question regarding anycasting in CDN setup Anurag Bhatia (Feb 01)
- Re: Question regarding anycasting in CDN setup Charles Gucker (Feb 01)
- Re: Question regarding anycasting in CDN setup Jared Mauch (Feb 01)
- Re: Question regarding anycasting in CDN setup Mike Jones (Feb 01)
- Re: Question regarding anycasting in CDN setup Anurag Bhatia (Feb 08)
- Re: Question regarding anycasting in CDN setup Anurag Bhatia (Feb 08)
- Re: Question regarding anycasting in CDN setup Brett Watson (Feb 08)
- Re: Question regarding anycasting in CDN setup Joe Provo (Feb 08)
- Re: Question regarding anycasting in CDN setup Anurag Bhatia (Feb 23)
- Re: Question regarding anycasting in CDN setup Anurag Bhatia (Feb 08)