On Wed, 20 Apr 2005 sthaug@nethelp.no wrote:
I'd rather expect this sort of behavior with anycasted servers...
Where do you see any connection between anycast and ignoring DNS TTL? Or is this just part of your usual rant against anycast DNS service?
The data he showed isn't necessarilly "ignoring ttl". If there are multiple anycasted caching servers behind a specific IP address, then those several cache's will each have a different state. Since, [as I explained, and was supposed by the poster], there is "some kind of load balancing going on", and also since implementors of anycast caches have posted questions and explained their purposes [which could be seen as "load balancing"], this is a likely explanation. It may not be the only explanation: e.g. they could be restarting their nameservers every thirty seconds. But "anycast loadbalancing" of a caching server is probably the most likely. But since you post on DNSOP, I assume that you read DNSOP [indeed, I may assume too much here], and so you have read the recent questions posed there on just how to implement just this sort of configuration. So, in light of that, I take your message to be your "usual [and fact-free] rant against anyone who explains the harms of anycast"
We use anycast for our caching (recursive) DNS servers. It works well for us, and we certainly intend to continue to use it. The actual DNS software used is Nominum CNS and BIND 9.3.1, both of which honor the DNS TTL.
"worked once for me" doesn't cut it, now. Does it? Probably you didn't notice that the cache states of different caching servers must be different. "load balancing" [of nearly any sort] and anycast does not work so well.
Steinar Haug, Nethelp consulting, sthaug@nethelp.no
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