Subject: [DNSOP] About DNS over TCP query pipelining

From: Francis Dupont <[email-masked]>
Date: Thu, 08 Jan 2015 18:06:04 +0100

I am working on the different aspects of the query pipeling (for DNS
over TCP or any stream / sequenced packet transport). I try a new tool
which sends multiple queries to check which authoritative nameserver
implementations support out-of-order responses with a funny result!
I never got a conclusive answer:
 - without unexpected things like on the fly signing auth servers are
  fast enough to send responses back to back
 - TCP (slow start?) and network (I tried from my home) delays are greater
  than server processing delays.
So is the pipelining and its head-of-line blocking avoidance idea not
appicable? No, and the RFC5966bis I-D is right with its "(especially
recursive)": the processing time of a recursive server depends on
external servers when the response is not in the cache. With DNSSEC
validating it should be easy to find cases with a big variation in
delays.
To finish there is a well known real world case where a client could
send a flow of queries over TCP to a recursive server: the forwarder
case. And more, it is not ridiculous to force the use of TCP with
a forwarder...
This leads to another question: how to keep the TCP connection opened
with a minimal cost (i.e., not sending keep alives :-). There is an
I-D about this (in another mailing list thread please).

Regards

[email-masked]

---

From: Tony Finch <[email-masked]>
Date: Thu, 8 Jan 2015 18:39:52 +0000

Francis Dupont <[email-masked]> wrote:

> I try a new tool which sends multiple queries to check which
> authoritative nameserver implementations support out-of-order responses
> with a funny result!

You can use adns to do this test too, e.g. with the --tcp query option to
adnshost. (Caveat: adnshost does not have any built-in backpressure so it
isn't great for bulk DNS lookups. I usually hack adnsresfilter for special
bulk lookup jobs like comparing performance of TCP-only with UDP-first.)

http://www.chiark.greenend.org.uk/~ian/adns/

Tony.
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