[dns-operations] forwarding to a forwarder

Doug Barton dougb at dougbarton.us
Tue Jan 19 03:52:20 UTC 2016

On 01/18/2016 05:45 PM, Dave Warren wrote:
> On 2016-01-18 11:13, Doug Barton wrote:
>> On 1/17/2016 8:43 PM, Randy Bush wrote:
>>> A is a bind 9 where foo.bar is forwarded to B
>>> can an unbound on C forward foo.bar to A?
>> Yes. The only disadvantage to this configuration is that you get
>> double-caching, so on average you'll have a full TTL period for a
>> change to make it all the way back to C. For this reason I always
>> recommend slaving instead of forwarding, but when that's not possible
>> this is the next-best solution.
> I'm not sure that changes caching vs a single resolver, does it?
> Shouldn't a caching resolver age the TTL on entries in it's cache, such
> that subsequent queries shouldn't end up over-caching, but rather, they
> should just get the remaining cache based on the original resolution.

In theory, yes, and I should have phrased my response differently. Your 
example was a good one, and illustrated how it should work.

That said, I've seen weird things happen with double forwarding, which 
is why I recommend slaving instead wherever possible. But if that's the 
best option, it works.


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