On Wed, Jul 8, 2015 at 2:39 PM, Robert Sparks <rjsparks(_at_)nostrum(_dot_)com>
wrote:
I am the assigned Gen-ART reviewer for this draft. For background on
Gen-ART, please see the FAQ at
<http://wiki.tools.ietf.org/area/gen/trac/wiki/GenArtfaq>.
Please resolve these comments along with any other Last Call comments
you may receive.
Document: draft-mm-netconf-time-capability-05
Reviewer: Robert Sparks
Review Date: 8 Jul 2015
IETF LC End Date: 29 Jul 2015
IESG Telechat date: not yet scheduled
Summary: This draft has open issues to address before publication
This draft adds two separable concepts to netconf
* Asking for and receiving knowledge of when a command was executed
* Requesting that a command be executed at a particular time
The utility of the first is obvious, and I have no problems with the
specification of that part of this extension. Would it be better to pull
these apart and progress them separately?
The utility of the second would be more obvious if the draft didn't limit
the time to be "near future scheduling". It punts on most of the hard
problems with scheduling things outside a very tight range (15 seconds in
the future by default), without motivating the advantages of saying "wait
until 5 seconds from now before you do this".
So:
Why was 15 seconds chosen? Could you add a motivating example that shows
why being able to say "now is not good, but 5 seconds from now is better"
is useful? (Something like having a series of things happen as close to
simultaneously without the network delay of sending the requests impacting
how they are separated perhaps?)
Given the punt, why isn't there a statement that sched-max-future MUST NOT
be configured for more than some small value (twice the default, or 30
seconds, perhaps), especially while this is targeted for Experimental?
Without something like that, I think the document needs to talk about more
of the issues it is trying to avoid with longer term scheduling, even if it
doesn't solve those issues. (If I have a fast pipe, I can make a server
keep a lot of queued requests, eating a lot of state, even if the window is
only 15 seconds. Pointing to how netconf protects against state-exhaustion
abuse might be useful).
Picking some arbitrary small sched-max-future value only lowers the
probability that
something goes wrong, so it is not a very good punt.
The security considerations section talks about malicious parties
attempting to cause sched-max-future to be configured to "a small value".
Could you more clearly characterize "small", given that the default is 15
seconds?
Even with the near-future limit, there are issues to discuss introduced
with the ability to cancel a request:
* What prevents a 3rd party from cancelling a request? I think it's only
that the 3rd party would have to obtain the right id to put in the cancel
message. If so, the document should talk about how you keep eavesdroppers
from seeing those ids, and that the servers that generate them should make
ids that are hard to guess.
Since the scheduled rpc event is sent to every client that is listening
for notifications, there is no possibility for security through
hard-to-guess token,
as is done with the "persist-id" for cancelling a confirmed-commit.
NETCONF has no support for sending a notification to just 1 session or user.
* Especially given the near-future limitation, you run a high risk that
the cancel arrives after the identified request has been executed. It's not
clear in the current text what the server should do. I assume you want the
server to reply to the cancel with a "I couldn't cancel that" rather than
to do something like try to undo the request. The document should be
explicit.
* The document should explicitly disallow adding <scheduled-time> to
<cancel-schedule>
One editorial comment: It would help to move the concept of the
near-future limitation much earlier in the document, perhaps even into the
introduction and abstract.
And for the shepherding AD: The document has no shepherd or shepherd
writeup. While a writeup is not required, one would have been useful in
this case to discuss the history of (lack of) discussion of the document on
the group's list and the group's reaction to progressing as Experimental as
an Individual Submission.
Andy