edns responses not sent by DNS Server

[Barry Margolin]

In article <mailman.206.1496135739.702.bind-users at lists.isc.org>,
 Harshith Mulky <harshith.mulky at outlook.com> wrote:

> Hello Mark,
> 
> Yes the client is retrying the query over TCP. 
> 
> But initially I am getting no Answers 
> The ANSWER is as below
> 
> ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id:  18094
> ;; flags: qr aa tc rd ad ; QUESTION: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL:
> 1
> ;; OPT PSEUDOSECTION:
> ; EDNS: version: 0, flags: do; udp: 4096
> ;; QUESTION SECTION:
> ;pcr21381.dflt.vzb.com.         IN      NAPTR
> 
> Should the server be sending some responses which are truncated (or) no
> Responses in this case?

BIND will omit the Additional Section (and maybe also the Authority 
Section?) if that allows the response to fit. Otherwise I believe it 
just sends an empty response, and the client is supposed to retry with 
TCP.

The problem with sending a partial Answer Section is that there's no way 
for the client to know if the omitted answers are important. So it has 
to retry anyway.

-- 
Barry Margolin
Arlington, MA