Re: DNS Anycast as traffic optimizer?

[Steve Francis <sfrancis () fastclick com>]

Christopher L. Morrow wrote:

> If I read your original request correctly you were planning on:
> 1) having presence in multiple datacenters (assume multiple providers as
> well)
> 2) having a 'authoritative' DNS server in each facility (or 2/3/4
> whatever per center)
> 3) return datacenter-1-host-1 from datacenter-1-authserver-1,
> datacenter-2-host-2 from datacenter-2-authserver-1, and so forth.
>
> This isn't really 'anycast' so much as 'different A records depending on
> server which was asked'
>  
Well, there'd be one NS record returned for the zone in question. That 
NS record would be an IP address that is anycasted from all the datacenters.
So end users (or their DNS servers) would all query the same IP address 
as the NS for that zone, but would end up at different datacenters 
depending on the whims of the anycasted BGP space.

Once they reached a name server, then yes, it changes to 'different A 
records depending on server which was asked'


> So, you'd be dependent on:
> 1) order of DNS requests made to AUTH NS servers for your domain/host
>  
As there'd only be one NS server address returned, that negates this point.

> 2) speed of network(s) between requestor and responder
>  
Or the closenes (in a BGP sense) b/w the requester and the anycasted DNS 
server.

> 3) effects of using caching DNS servers along the route
>  
True. But I'm not trying to cope with instantly changing dynamic conditions.

> I suspect you'd really also introduce some major
> troubleshooting headaches with this setup, not just for you, but for your
> users as well.
>  
I don't doubt that. :-)