Subject: [Doh] EDNS UDP Payload size cache issue

From: bert hubert <[email-masked]>
Date: Wed, 6 Jun 2018 14:12:58 +0200

Hi,

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.

Bert.

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From: Star Brilliant <[email-masked]>
Date: Wed, 6 Jun 2018 12:45:07 +0000

>    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.