Re: [OPS-NM] Comments on XSDMI BoF proposal

David Harrington wrote:
> Hi,
> 
> comments inline 
> 

ditto

> (I am cross-posting to the ops-area mailing list because no official
> decision was made to relocate discussion for XSDMI to the ops-nm list.
> I will ask Dan to change the BOF page to direct discussion to the
> ops-nm list. Interested parties please find XSDMI discussion on the
> ops-nm list.)
> 
> dbh
> 
>> -----Original Message-----
>> From: Andy Bierman [mailto:ietf@andybierman.com] 
>> Sent: Monday, June 04, 2007 1:15 PM
>> To: Ops-Nm
>> Subject: [OPS-NM] Comments on XSDMI BoF proposal
>>
>> General:
>>
>> I strongly support the formation of this WG, and think
>> it should be the "only next step" in NETCONF Data Modeling
>> standards development.
> 
>> Trying to standardize too much at once without enough implementation
>> experience is not going to help.  The most critical DM need is to
>> figure out how to use the standard NM data definitions we 
>> already have.
> 
> My intention is to develop a way to access MIB data via XML-based NM
> protocols,
> to take advantage of the existing NM data definitions in the MIB. 
> 

This is fine, but it should be based on use cases, as you say later on.
IMO, there is a use case to read MIB data via a NETCONF session.
The goal can be abstract, but the solutions has to be specific,
in order to have an inter-operable standard.

> This is a migration strategy to move from a mainly-SNMP-and-MIB
> management framework to a multi-protocol-and-multi-data-model
> management framework. 
> 
> I do not think MIB access is enough. A binary data-based approach like
> the MIB is fine for automated management, but it is not good for
> operator-interactive management, and it fails to take advantage of
> advances in computer networking technology like WWW technologies.
> 

I am not interested in an SNMP-like interface to SMI data, encoded in XML.
IMO, via NETCONF <get>, the access should be per-row-instance, via subtree
and Xpath filters, not per-column-instance, via lexi-next (getnext).

Other protocols will have completely different requirements and
retrieval operations, and the solution might not be the same.

> For operator-interactice NM, I think we need task-based NM interfaces.
> The CLI is one approach, and standardizing it would probably be
> helpful, but the engineering departments of vendors are not very
> cooperative on doing that; it is easier for engineers to use freeform
> text when developing CLIs and syslog-style reporting than to use
> standardized content. 
> 
> XML-based management leverages lessons learned from the WWW. While
> document-based rather than command-based, tasks can often be grouped
> into a document-type interface, such as a web page. With automated
> translation from XML into HTML (and related technologies), we can work
> on developing task-based-document NM interfaces. 
> 
> I think we need to spend more time thinking about operator use-cases,
> not just technical designs of SMIs. I think it would help to start
> thinking in terms of modular data models similar to MIB modules, not
> just a <running> config,  but we need to develop an SMI that helps to
> differentiate config and state info, which SMIv2 doesn't do, Maybe all
> we need to do is recommend that MIB modules have separate subtrees for
> config and for state, much as we now recommend separate subtrees for
> objects and notifications. 
> 
> While I would like to see the reuse of existing standards, such as
> XSD, we need to support programmatic interfaces to allow (incremental)
> automation of repetitive tasks. That means we need to provide
> machine-readable "clues" about the meta-nature of management
> information. Maybe that can be done in XML using attributes, or
> namespaces, or hierarchical organization. Maybe it will require a new
> SMI with all the special fields found in SMIv2 - and more. 
> 
> I think one of the big questions we need to address is whether a new
> SMI should be developed that is an extension/superset of SMIv2, or is
> distinct from SMIv2. I think that work involves getting operator
> feedback of how they work, so we can understand whether we should be
> trying to merge the existing NM protocols, or should keep them (and
> their data) distinct. I think we should be considering how to
> componentize existing standards work, so we can reuse some parts, such
> as secure transport, while keeping other parts distinct. 
> 
> That work can advance while we work on developing support for one or
> more XML-based interfaces to SMIv2 data models, as a migratory step
> toward multi-protocol management.
> 
>> Nit: The WG acronym is kind of cryptic and I'm not sure what
>> it supposed to mean.  Also, the WG name only describes work items
>> (A) and (B).  Security requirements for multi-protocol access
>> to MIB data is definitely not covered by the title, and (D)
>> is 'possibly' NETCONF protocol-specific. (?? XSMI ?? SMIX ?? 
>> SMINET ??)
> 
> I deliberately avoided the use of SMI. As somebody pointed out (you?),
> this work (A and B) is not developing a new SMI, it is merely
> translating elements of SMIv2 from one language to another.
> 

I do not think this limited and generalized translation (D) is very useful,
or realistically possible to do well in the IETF, in finite time.

I prefer to view the Network Management problem in specific terms, e.g.,
understanding how conceptual data defined in SMIv2 can be mapped
into a NETCONF Configuration Database, and accessed with NETCONF
protocol operations.

Abstracting the NM problem as if there was nothing going on beyond
editing the XML instance document itself does not really help.

>> Milestones:  Any idea how long you think it will take to do
>> all this work?
>>
>> Work items:
>>
>> (A)(B)
>> The XSD for SMIv2 data types and TCs draft has been reviewed 
>> and refined
>> over
>> a couple years, and it is very much needed, and ready, for 
>> standardization.
> 
> Yan will be publishing a base datatype translation document, based on
> libsmi translations. Since this has been defined and used(?) fo
> ryears, I expect this should be fast - in IETF terms, we can probably
> finish in seven or eight years ;-). Seriously, I hope this can be done
> in six months or so, if there is enough interest to work on it.
> 
> That will be supplemented by the (romascanu) TC translations document.
> We need to decide whether XSD can express the restrictions adequately
> to support machine-validation, and whether the amount of
> machine-validation supported justifies having an XSD for the TC.
> Having TC translations might be helpful for netconf to go read existng
> MIB data, without having to also parse SMIv2 MIB documents to
> understand what the values mean. I think the bigger benefit is
> defining TCs that can be used by multiple protocols to support
> consistent semantics across protocols, and XML is the preferred
> language for most new protocols.
> 
> This will require case-by-case analysis, and might take time to reach
> consensus. Of course, not every contentious TC must be included in
> this document, so if we cut out the contentious ones, this should be
> able to be wrapped up within a year, I hope.
> 
>> (C)
>> This work item is a bit vague.  I'm not sure if it means
>> a mapping between an SNMP EngineID to a NETCONF session identity,
>> or something to do with VACM, or something else undefined.
>> I think it is a smart idea to understand all the security issues
>> associated with (D).
> 
> I'm looking at the bigger picture of multi-protocol management. There
> are lots of protocols being developed, both inside and outside IETF,
> to perform management functionality. As Bob Natale pointed out, the
> MIB is the "crown jewel" of IETF Management (I think SNMP is as well,
> when used for what it is good at). I think lots of WGs and lots of
> other SDOs are going to look at the MIB and say "gee, we should
> leverage that!"
> 
> I think we need to set some guidelines about how protocols should deal
> with the MIB, so that it is not ruined by unconstrained access by
> multiple protocols, especially write access.
> 
> But even read-access can be problematic. Security is a process, not a
> product. The IETF needs to decide how to "balance" security in an
> environment of multi-protocol management. It makes no sense to protect
> your house with a front door that has multiple deadbolt locks, if your
> back door has no locks. 
> 
> It makes no sense to expect operators to go to the trouble of
> configuring VACM to protect the data in the MIB when using SNMP, if
> the operator's VACM configuration will just be ignored by netconf and
> other protocols accessing the MIB. I think we need some guidelines
> that provide for a more consistent approach to multi-protocol MIB
> access, than VACM-for-SNMP and nothing-for-others. 
> 
> Personally, I would like to see VACM not be mandatory-to-implement for
> SNMP, if there is no corresponding mandatory-to-implement access
> control for other protocols. I don't think the operator community is
> actually ready for standardized cross-protocol access control, and if
> it isn't balanced across protocols, then we shouldn't require any NM
> protocol standards to have a mandatory-to-implement access control
> model.
> 

Previous discussions wrt/ NETCONF access control have indicated
that a simple solution allowed just 2 access levels (read and write)
is favored.  Perhaps as a backlash to VACM.

>> (D)
>> I support a standard algorithmic translation between SMIv2
> conceptual
>> data models and NETCONF configuration databases, which includes
>> data organization and standard protocol operation mappings.
>> I think read-only access instead of full access will be easier
>> to achieve, so it should be done first.  The use case for
>> write access is not as strong, and the multi-protocol access and
>> security issues are harder.
> 
> I agree that read-only access would probably be sufficient for netconf
> to gather state information, statistical information, and
> notifications. I do not see a lot of reason to support write access to
> the MIB via netconf.
> 
>> I do not support a generic XSD representation of SMIv2 macros,
>> without consideration of the specific XML-based protocol being used.
>> The 'embedded' SNMP protocol operations in SMIv2, as well as 
>> the explicit
>> SNMP operations discussed in MIB object DESCRIPTION clauses, 
>> RowPointer,
>> RowStatus, StorageType, etc., all have to be explicitly mapped to
> the
>> specific NETCONF (or whatever) protocol operations and
>> architecture assumptions.
> 
> I think these need to be supported to understand the values of certain
> fields that might be read from the MIB. 
> 
> RowStatus reflects the operational state of the row, and if netconf is
> accessing the MIB to determine operational state of the thing
> represented by that row, it is an important piece of information. But
> if netconf has no write capability to the MIB, it does not need to
> know how to manipulate the values.
> 
> StorageType is also state information about a row that might be
> important for a netconf client to understand; it might be helpful to
> know that the MIB representation (or the underlying instrumentation)
> is in ROM. But if it has no write capability, it does not need to know
> how to manipulate the row within the constraints of StorageType. 
> 
> The MIB is more or less a relational database, where the relations
> between rows is important information. If netconf reads a row that has
> a relationship to another row via a RowPointer, netconf better know
> how to interpret a RowPointer.
> 
> (It is important to understand that I make no assumptions that a
> netconf-client will have a direct connection to an SNMP manager that
> knows how to parse this information from an SMIv2  MIB module
> document.)
> 
> I think we need to walk through these TCs on a case-by-case basis to
> decide whether we need each one for use with netconf, and what XSD
> restrictions apply.

I was pointing these complexities out as a reason not to deal
with write access.  If there are products used by operators someday,
that have some sort of XML-based "set" operation for MIB data,
then maybe it would be interesting to standardize it.

> 
> David Harrington

Andy

_______________________________________________
OPS-NM mailing list
OPS-NM@ietf.org
https://www1.ietf.org/mailman/listinfo/ops-nm