hello,
Based on Seoul IETF's discussion, I refine the introduction of this
document to explain the motivation and compare with other mechanisms.
the key text is here:
---------------------------------------------
1. Introduction
Sometimes, when DNS lookup of X, an application will lookup Y if X
fails. For examples, the initiator may fall back to A record if the
lookup of MX record fails.
Some initiators do it in sequence, X and after a few seconds, then Y.
Although it is simple, this leads to unpleasant waiting whenever X
times out or answers negatively.
Some initiators use concurrent X/Y lookups and a state machine to
decide whether to use X or Y. If an answer to Y arrives but none to
X, the initiator needs to wait a little or else fall back to Y
inappropriately. Concurrent lookup is faster if the X lookup takes
time and falling back to Y is appropriate, but rather complex, with
four states to test, and the initiator needs to wait for an answer to
X or a timeout before it can use Y.
This document enables a quicker, more easily tested failover. There
is no need to test different answer sequences, there's no need for a
state machine, there's no need for timeouts beyond receiving the
reply. This document describes a method by which DNS initiators can
send a main question accompanying with several related questions in a
single DNS query, and enables DNS responders place all related
answers into a single DNS response. This mechanism can reduce the
number of DNS round-trips per application work-unit, by carrying
several related queries in a single query transaction. It has the
following advantages compared to other solutions.
o Compared to sequential lookups: It's roughly as simple, but much
faster in case a fallback to Y is necessary.
o Compared to the concurrent mechanism: It is slightly faster (if
the initiator needs to wait for an X timeout) and/or prevents
inappropriate fallback (if the answer to X arrives too late), and
it has a simpler state machine.
This mechanism can also be used in the scenarios when the application
needs more records of the same domain name or its sub-domain name.
For examples, when asking about a QTYPE=A RRset, a QTYPE=AAAA RRset
may also be of use [RFC 5321]; When asking for some RRset of
www.example.com about A and AAAA, records of a sub-domain name such
as _443._tcp.www.example.com for TLSA may be of interest[RFC 6698].
--------------------------------------------
Jiankang Yao
From: internet-drafts
Date: 2017-06-23 15:41
To: XiaoDong Lee; Ning Kong; Paul Vixie; Jiankang Yao; Xiaodong Li
Subject: New Version Notification for
draft-yao-dnsop-accompanying-questions-03.txt
A new version of I-D, draft-yao-dnsop-accompanying-questions-03.txt
has been successfully submitted by Jiankang Yao and posted to the
IETF repository.
Name: draft-yao-dnsop-accompanying-questions
Revision: 03
Title: A DNS Query including A Main Question with Accompanying Questions
Document date: 2017-06-23
Group: dnsop
Pages: 11
URL:
https://www.ietf.org/internet-drafts/draft-yao-dnsop-accompanying-questions-03.txt
Status:
https://datatracker.ietf.org/doc/draft-yao-dnsop-accompanying-questions/
Htmlized:
https://tools.ietf.org/html/draft-yao-dnsop-accompanying-questions-03
Htmlized:
https://datatracker.ietf.org/doc/html/draft-yao-dnsop-accompanying-questions-03
Diff:
https://www.ietf.org/rfcdiff?url2=draft-yao-dnsop-accompanying-questions-03
Abstract:
This document enables DNS initiators to send a main question
accompanying with several related questions in a single DNS query,
and enables DNS responders to put the answers into a single DNS
response. This extension enables a range of initiators to look up
"X, or failing that, Y" in a better way than both current
alternatives. This mechanism can reduce the number of DNS round-
trips per application work-unit.
Please note that it may take a couple of minutes from the time of submission
until the htmlized version and diff are available at tools.ietf.org.
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