Subject: [ippm] Comments on draft-mizrahi-owamp-twamp-checksum-trailer

From: Brian Trammell <[email-masked]>
Date: Thu, 12 Dec 2013 16:38:31 +0100

Greetings, all,

(chair hat off)

At the request of its author, I've taken a look as an individual
contributor at draft-mizrahi-owamp-twamp-checksum-trailer.

The draft describes a relatively straightforward and interoperable
method for keeping UDP checksums valid during post-transmission
modification of OWAMP and TWAMP packets, specifically to allow modifying
timestamps in hardware for more accurate timing information. This
definitely seems like a useful thing to have.

I have only one complaint, and that is that the draft is not named so as
to allow convenient tracking in the datatracker as an individual draft
targeted to the IPPM working group, and would suggest that a future
revision of the draft be named
draft-mizrahi-ippm-owamp-twamp-checksum-trailer.

A couple of comments/questions:

(1) Section 3.4. recommends that authentication and the checksum trailer
not be used together. I presume that this arrangement would also not be
compatible with draft-ippm-ietf-ipsec for similar reasons?

(2) The draft presumes that the timestamping hardware and OWAMP/TWAMP
implementation are implemented together. When this is not the case
(i.e., if we want interop between timestamping hardware and OWAMP/TWAMP
implementations from different sources): Does/should the draft have any
guidance for what a timestamping hardware device should do if it does
not detect sufficient padding to add a checksum trailer and/or detects
that the final two octets of the padding may be used for some other purpose?

Best regards,

Brian (again, as individual)