Re: [Doh] EDNS UDP Payload size cache issue

Star Brilliant <m13253@hotmail.com> Wed, 06 June 2018 12:45 UTC

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From: Star Brilliant <m13253@hotmail.com>
To: "doh@ietf.org" <doh@ietf.org>
Thread-Topic: [Doh] EDNS UDP Payload size cache issue
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Date: Wed, 6 Jun 2018 12:45:07 +0000
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Subject: Re: [Doh] EDNS UDP Payload size cache issue
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bert hubert <bert.hubert@powerdns.com>; wrote:

> The draft suggests zeroing the DNS ID field to make sure queries can be
> cached. One other field that needs to be made constant is the EDNS payload
> size. If a client requests DNSSEC, there will always be such a field, but it
> has no meaning over DOH. So it can safely be set to zero.
>
> Suggested text for insertion near the end of "5.1 The HTTP Request":
>
>    Similarly, if an EDNS payload size is specified, it SHOULD be set to 0 in
>    every DNS request, as this field has no meaning within this protocol.


I vote up for this idea.
But why "0", instead of other values (e.g. 65535)?

Also I would like to say something negative about this proposal:

1) It would require more code to implement. Using a DNS message parser library may make the implementation easier, but I am not sure every one wants this, especially because it may fail when later EDNS versions are released in the future.

2) I do not see any benefit for doing it. It does not reduce cache pressure either: common value is almost always 4096.