[dns-operations] NS1 nameservers response size

Mark Andrews marka at isc.org
Fri May 24 23:36:37 UTC 2019

> On 24 May 2019, at 11:16 pm, Paul Vixie <paul at redbarn.org> wrote:
> On Friday, 24 May 2019 11:34:38 UTC Mark Andrews wrote:
>> ...
>>> On 24 May 2019, at 21:10, Jan Včelák <jv at fcelda.cz> wrote:
>>> I can confirm we do not respect the buffer size. We are aware of this
>>> deficiency but it also doesn't have high priority at the moment.
>>> Have you encountered a situation where it has been causing trouble for a
>>> real application? Or is this an accidental discovery?
> when they tell you their buffer size, they are telling you that nothing larger 
> than that will be received. this signaling is not advisory; if you ignore it, 
> your response will appear to be truncated or malformed (if you're lucky).
> you would literally be better off, and more correct, if you just ignored or 
> servfailed any query whose buffer size parameter was smaller than your 
> intended answer. (or you could respond with TC=1 and no answers.)

And when TC=1 is sent make sure the OPT record is included if it is a response
to a EDNS request.  This is required by EDNS but some servers don’t do this.


Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742              INTERNET: marka at isc.org

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