Negative Caching of DNS Responses for Different RCODES

[Tony Finch]

Harshith Mulky <harshith.mulky at outlook.com> wrote:
>
> 1. How is Negative Caching Applied for other RCODES : FORMERR, SERVFAIL,
> REFUSED and NOTIMPL? What is the minimum TTL Value for these responses?

Good question: this isn't well specified. BIND has servfail-ttl (1s by
default) and lame-ttl (600s by default). The lame-ttl can take effect in
as a result of REFUSED responses amongst other things. NOTIMPL should not
normally occur. FORMERR can trigger EDNS downgrade.

> 2. Are the clients free to re-query the same DNS server if no caching is
> applied for the above RCODES?

In general the same question will yield the same answer so a good
implementation should avoid and preferably suppress repeat queries.

Tony.
-- 
f.anthony.n.finch  <dot at dotat.at>  http://dotat.at/
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Good.