Greg Woods writes:
[Tirade against aol.com, which I mostly agree with]
> More advanced nameservers
> can also selectively hand out very short TTL responses based on system
> load balancing policy, etc. (though don't use that lbnamed perl script
> for production -- it fails silently under load), but of course there's a
> tradeoff here with the increased DNS bandwidth you'll need to support.
And what about the extra load you are putting on people who want to send
you mail? Currently aol.com has an original TTL of 1 hour on the CNAME
and A records (1 day on the MX's), which I think is just about acceptable.
The point is that MTAs like Exim, at any rate, are going to collect the
complete set of possible recipient IP addresses, working through multiple
MX's and multiple A's, during a routing phase. This is quite a lot of
resolver calls with any of these schemes, and one really does want the
results to be cached in a local nameserver for a decent interval thereafter.
Chris Thompson Cambridge University Computing Service,
Email: cet1@??? New Museums Site, Cambridge CB2 3QG,
Phone: +44 1223 334715 United Kingdom.
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