Re: [netmod] AD review of draft-ietf-netmod-system-mgmt

[Juergen Schoenwaelder <[e-mail]>]

Hi,

I believe we need a reality check here. Unfortunately, I do not have
access to many recent devices. I would like to know what todays devices
do if you configure properties via the CLI that are export via SNMP
agents.

- Do boxes reject anything at the CLI that does not conform to
  DisplayStrings?
- Or do CLIs accept stuff and the agents provide strings not
  conforming to DisplayStrings?
- Or do CLIs accept stuff and there is implementation specific
  translation happening?

For me, US 7-bit ASCII forever can't really be the answer.

/js

PS: At least on common *nix systems, the SNMP agent is a completely
    separate process - one out of many. If I change the name of my
    interface (and I can change it pretty arbitrarily), the SNMP agent
    is not being asked and it has to deal with the name it finds the
    kernel using. Some of the popular SNMP code bases out there not
    even manage to properly truncate strings to DisplayString size. I
    know it is a weak argument but in the real world, I am sure
    management systems already have to deal with these issues.

On Thu, Dec 12, 2013 at 12:08:03PM -0500, ietfdbh wrote:
> Hi,
> 
> Personally, I think it would be simpler to just have the YANG objects be
> constrained by DisplayString syntax, but then, I come from a country where
> 7-bit ASCII covers my language of choice. It would be nice to have a
> consistent underlying instrumentation without duplication of effort and
> resources, but that would require choosing the least common denominator
> (DisplayString). 
> 
> My second choice would be to treat them as separate instances, one of
> DisplayString syntax, one of YANG string syntax. That way, we don't have to
> worry about side effects of changing the YANG object via the MIB, or
> changing the MIB object via YANG. If we want to internationalize the syntax,
> you cannot do that to the MIB within SMI limits. Mapping between them if
> they support different syntax raises a whole lot of issues for the database
> handling and UI of an NMS, stands the chance of breaking existing
> implementations if implementers handle the translations wrong or in a
> non-interoperable manner, and stands the chance of misleading operators (and
> applications) if the value of the MIB object is changed dynamically because
> the value is changed (in any way) via translation from the YANG object. 
> 
> I think it would be better for standardization and interoperability if we do
> not try to force-feed new syntax into the existing MIB object(s). If you
> were trying to do this by updating the MIB, you would most certainly need to
> define a new object (much like we had to do with Counter64s to replace
> Counter32s). If the YANG object is treated as a separate object from the MIB
> object, then if and when the MIB is updated, the MIB can add an object to
> map to the YANG object, and deprecate the DisplayString syntax object.
> 
> If the YANG object says it can be mapped, then I think the YANG object must
> REQUIRE that it be implemented with DisplayString constraints, whether a
> server implementation maps to the MIB or not. Assuming an NMS supports both
> MIB and YANG queries, and an implementer MAY treat them as separate, then
> the NMS must treat them as separate. If the implementer MAY treat them as
> mapped, the NMS still needs to implement them as separate because they MAY
> be separate, but the NMS probably must treat the NMS-side variables as
> mapped to ensure they are in sync; otherwise reading the value via the MIB
> without simultaneously reading the value via YANG would lead to the NMS
> potentially displaying different values even though on the device the values
> are the same. This optionality greatly increases the complexity of
> implementing these objects on the NMS side. An NMS would need to determine
> whether the agent/server implemented these as mapped or separate, presumably
> by changing one and seeing if it affected the other, so it knew whether to
> try to perform synchronization between the two. Lots of work for limited
> benefit to the operator. And if NMS implementations handled synchronization
> differently, the operator is stuck trying to manage with conflicting
> information from different NMSs.
> 
> It would be much better to standardize the expectation - either these
> objects MUST be mapped and constrained by DisplayString syntax per the IETF,
> or MUST be defined as separate objects of different syntax per the IETF
> standard. Then an NMS implementer knows what to expect.
> 
> David Harrington
> [e-mail]
> [phone]
> > -----Original Message-----
> > From: netmod [mailto:[e-mail]] On Behalf Of Randy
> > Presuhn
> > Sent: Thursday, December 12, 2013 3:43 AM
> > To: Martin Bjorklund
> > Cc: [e-mail]
> > Subject: Re: [netmod] AD review of draft-ietf-netmod-system-mgmt
> > 
> > Hi -
> > 
> > > From: "Martin Bjorklund" <[e-mail]>
> > > To: <[e-mail]>
> > > Cc: <[e-mail]>; <[e-mail]>
> > > Sent: Wednesday, December 11, 2013 11:52 PM
> > > Subject: Re: [netmod] AD review of draft-ietf-netmod-system-mgmt
> > >
> > > Randy Presuhn <[e-mail]> wrote:
> > > > Hi -
> > > >
> > > > >From: Juergen Schoenwaelder <j.schoenwaelder@jacobs-
> > university.de>
> > > > >Sent: Dec 11, 2013 12:38 AM
> > > > >To: Randy Presuhn <[e-mail]>
> > > > >Cc: [e-mail]
> > > > >Subject: Re: [netmod] AD review of draft-ietf-netmod-system-mgmt
> > > > >
> > > > >On Tue, Dec 10, 2013 at 01:18:10PM -0800, Randy Presuhn wrote:
> > > > >
> > > > >> > Anyway, for a standardized approach, someone would have to write
> > a
> > > > >> > document that defines how unicode code points are represented as
> > > > >> > escaped charater sequences in DisplayStrings. I do not think that
> this
> > > > >> > document is in charge of doing this. Hence, until such a standard
> is
> > > > >> > written, I think things need to be implementation specific.
> > > > >>
> > > > >> Perhaps, though that is the route to being stuck with ASCII until
> the
> > > > >> successor to Netconf rolls along.
> > > > >
> > > > >Not necessarily. If you configure via NETCONF (or most CLIs these
> > > > >days), you can use unicode characters. The code that maps names to
> > > > >legacy non-unicode interfaces then needs to do suitable translations
> > > > >to fit whatever constraint there is.
> > > >
> > > > Not if the data definition restricts the values to an ASCII
> > > > subset, as has been proposed.  What's in the draft at the
> > > > moment will bring its own interoperability problems, but
> > > > at least it's a baby step forward.
> > >
> > > So it seems we have a chance to fix this now.  But I need to
> > > understand what exactly you and/or Juergen propose.  Preferrably
> > > concrete text.  I *think* that the proposal is something like this:
> > >
> > >    o  An implementation MUST allow any legal "string" (YANG string).
> > 
> > There are good reasons to restrict formatting and control characters -
> > I'll assume YANG strings do this already.  If not, that's another long
> > discussion.
> > 
> > >    o  An implementation that maps this value to the corresponding MIB
> > >       object, which has size and character set limitations, MUST use
> > >       some mechanism out of the scope for this document to ensure that
> > >       the MIB object syntax is still valid.
> > 
> > Yes this seems reasonable.
> > 
> > But it doesn't cover a "round trip".  If the value is modified via the MIB
> > interface to include what looks like the implementation-specific encoding
> > into ASCII of a non-ASCII Unicode code point, does retrieving that value
> > via the Netconf interface get the Unicode code point or the
> implementation-
> > specific ASCII encoding of it?  If it does (and I think it should) then
> there
> > needs to be some though put into what happens when the code point
> > encoded using ASCII would, if converted to Unicode, be illegal (for
> > whatever reason) in the YANG string.  It's probably best to keep the
> > SNMP instrumentation ignorant of all this, so code in the Netconf side
> > would need determine whether any of the ASCII "escape sequences"
> > would produce forbidden code points, and, in such cases, *not* evaluate
> > those sequences and just pass them through unevaluated.
> > 
> > 
> > > Also, just to make sure, we are talking about:
> > >
> > >    system/location        -- sysLocation
> > >    system/contact         -- sysContact
> > >    interface/description  -- ifAlias
> > 
> > Perhaps also sysDescr (even though read-only, my comment above seems
> > applicable,
> > particularly since on at least some systems this comes from a static
> > configuration
> > file, and would be useful to support local language in some minimal way.)
> > 
> > sysName (think IDN) might also be worth thinking about.  There was a long
> > debate
> > about this a while back; I don't know what current thinking is.
> > 
> > Randy
> > 
> > _______________________________________________
> > netmod mailing list
> > [e-mail]
> > https://www.ietf.org/mailman/listinfo/netmod
> 
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-- 
Juergen Schoenwaelder           Jacobs University Bremen gGmbH
Phone: [phone]         Campus Ring 1, 28759 Bremen, Germany
Fax:   [phone]         <http://www.jacobs-university.de/>