Subject: [DNSOP] comments on draft-ietf-dnsop-5966bis-02

From: 神明達哉 <[email-masked]>
Date: Tue, 28 Jul 2015 07:28:12 +0900

I have a couple of minor comments on 5966bis-02:

- Section 8

   For reasons of efficiency, DNS clients and servers SHOULD transmit
   the two-octet length field, and the message described by that length
   field, in a single TCP segment.

I suspect we cannot reasonably require this (with a "SHOULD") at the
level of DNS client/server implementation since an application cannot
always/fully control a specific TCP segment contains how much data: it
depends on the state of the TCP connection, specific implementation
details of the TCP stack, etc.  I suggest rephrasing this as follows
(and I guess that was actually what was intended to say here):

   For reasons of efficiency, DNS clients and servers SHOULD pass
   the two-octet length field, and the message described by that length
   field, to the TCP layer at the same time (e.g., in a single write()
   system call) so it will be more likely that all the data will be
   transmitted in a single TCP segment.  This additionally avoids
   problems due to some DNS servers being very sensitive to timeout
   conditions on receiving messages (they may abort a TCP session if
   the first TCP segment does not contain both the length field and
   the entire message).

- Appendix A

   TCP does not suffer from UDP's issues with fragmentation.

Exactly what does this mean?  Is this to say IP fragmentation won't
happen for TCP?  Or does this mean even if fragmentation occurs TCP is
free from the "UDP's issues" (what are they, btw)?

My impression from this sentence is that it assumes path MTU discovery
is used for TCP and fragmentation should normally not happen for TCP.
If this is the intent, I think it will need to explain a bit more,
including this particular assumption and why UDP can't benefit from
it.  If my impression is incorrect, I'd like to understand what it
actually tries to say.

--
JINMEI, Tatuya