The justification in the introduction is misleading:
This document specifies an EDNS0 extension that allows a validating
Resolver running as a Forwarder to open a TCP connection to another
Resolver and request a DNS chain answer using one DNS query/answer
pair. This reduces the number of round-trip times ("RTT") to two.
If combined with long livd TCP or [TCP-KEEPALIVE] there is only 1
RTT.
Without this extension the typical number of RTTs required is 1, so this
isn't a reduction.
There is also no guarantee
that the initial set of UDP questions will result in all the records
required for DNSSEC validation. More round trips could be required
depending on the resulting DNS answers.
With this extension you still require 2 RTT if the target is SRV or MX,
and maybe if it is CNAME or DNAME depending on how much the server decides
to return. Maybe it requires 3 RTT if the server decides it doesn't like
doing chain queries any more.
It occurs to me that you could get a lot of edns-chain-query's bandwidth
saving with a simple "minimal responses please" query flag.
Tony.
--
f.anthony.n.finch <d...@dotat.at> http://dotat.at/
Irish Sea: Southwest 5 to 7, occasionally gale 8 at first, becoming variable
4. Moderate or rough, becoming slight or moderate. Fair. Good.
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