[dns-operations] More Aggressive prefetch for popular names

Paul Hoffman phoffman at proper.com
Mon Apr 8 14:05:53 UTC 2019

It sounds like you are saying "some resolver operators extend the TTLs 
given in DNS responses, and this causes problems". If so, we agree.

If, however, you are saying "some resolver operators extend the TTLs 
given in DNS responses, and this causes problems that the rest of the 
DNS community should solve", we disagree. The customers of that resolver 
will have problems like the one you listed, and that is fully the fault 
of the resolver operator.

On 7 Apr 2019, at 21:26, Davey Song wrote:

>  Local resolver has policy/strategy to set a larger TTL to reduce the
> upstream traffic, in order to increase the cache hit rate and response
> time. Some times, local resolver has policy to serve stale data in 
> case of
> network failure after TTL timeout. There may be others situation cause 
> the
> cache serve stale data.

This is a misconfiguration on the part of the resolver operator.

> If any intentional operation, or software bug, or manual 
> misconfiguration
> on resolver will cause the serve-stale situation which will become a
> problems for names changing their records like NS, A/AAAA during the 
> period
> of stale data in the cache but not others keep unchanged.
> The recent event happened last week was a name of CCTV VOD services, 
> people
> call in complaining they can not open the video. It was found that in 
> Gang
> Zhou City, the DNS of a local broadband service provider served stale 
> data
> for that name for hours. It is not clear which conflict or bug make 
> the
> trouble, but the fact is cache of that local ISP and downstream 
> forwarder's
> cache got impact. It takes time to purge that cache.

Exactly right. That resolver operator should investigate the bug (most 
likely in their configuration, possibly in the unnamed resolver software 
they are using, and prevent it from happening in the future.

> I did it in the above. It does not sound like an exaggeration, I 
> think. If
> you are talking with CDN/Cloud people, this is a typical operation 
> issue
> they need to face.

It is not "typical": we rarely hear of this problem.

>  No. DNS in ISP and Teleco did something wrong.

One which can be fixed.

> As you are one author of
> DOH, you must konw how name owners want to bypass the DNS in the 
> middle.

This makes no sense. DoH was developed so that applications can use 
resolvers securely using HTTP semantics; that's completely unrelated to 
what you have said above.

--Paul Hoffman

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