Negative Caching of DNS Responses for Different RCODES

[Harshith Mulky]

Hello experts,

If a DNS server looks up a record and it's missing, it will often "negatively cache" the fact that this record is missing, and not try to look it up again for a while.
>From RFC 2308, Negative Caching of DNS Queries, I understood, the TTL for NXDOMAIN RCODE responses is taken from SOA Record at the top of the Zone.

My Questions
1. How is Negative Caching Applied for other RCODES : FORMERR, SERVFAIL, REFUSED and NOTIMPL? What is the minimum TTL Value for these responses?
2. Are the clients free to re-query the same DNS server if no caching is applied for the above RCODES?

Thanks
Harshith
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