Resolver behavior on expired TTLs

[Matus UHLAR - fantomas]

On 21.02.13 10:38, John Miller wrote:
>Here's something I hadn't put much thought into until recently--it's 
>never been a problem--how do resolvers behave when they receive a 
>request for an expired entry in the cache, but cannot contact the 
>authoritative nameserver?  I'd imagine they return a SERVFAIL, but I 
>could see NXDOMAIN as well.  Does anyone know the answer?

they should not sent anything but SERVFAIL if they are unable to do the
resolution. SERVFAIL should cause the client ask other server, while
NXDOMAIN means that the host does not exist and client can stop searching.

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