Subject: [dns-privacy] Tsvart last call review of draft-ietf-dprive-padding-policy-04

From: Magnus Westerlund <[email-masked]>
Date: Wed, 04 Apr 2018 02:30:34 -0700

Reviewer: Magnus Westerlund
Review result: Ready with Issues

I have reviewed this document as part of TSV-ART task to review documents with
potential transport related issues.

I note that the document in its final recommendation regarding block sizes do
consider MTU for reasonable size choices. What I am missing in Section 4 is the
discussion of MTU as impacting this. From my perspective, it appears reasonable
to: In Section 4.1 consider if the Block Size will interact with the MTU.
Especially for block sizes that are a small fraction of the MTU, unless the
block is chosen so that a multiple just fits the MTU, the block padding may
cause unnecessary fragmentation for UDP based delivery. Also chosing a block
size larger than the MTU of course forces one to always fragment.

In Section 4.2 I think depending on the negotiated size, the downside is that
it will commonly result in a consistent number of fragments reducing delivery
probability. I haven't digged into the negotiation part about maximum response
size. But, I assume that this is not necessarily chose based on MTU
constraints, but other limitations in the system.

Note that these comments only applies for datagram based transport without its
own fragmentation mechanism, e.g. UDP.