Last Call Review of draft-ietf-mpls-tp-te-mib-09
review-ietf-mpls-tp-te-mib-09-genart-lc-davies-2014-12-11-00

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Document: draft-ietf-mpls-tp-te-mib-09.txt
Reviewer: Elwyn Davies
Review Date: 10 December 2014
IETF LC End Date: 8 December 2014
IESG Telechat date: (if known) -


Summary:


Not  ready.  I am not a MIB expert nor an MPLS(-TP) configuration 


expert, so I have



assumed that the details of the MIB specification have been addressed by


Joan's MIB Doctor review and the configuration examples have been 


checked by an


MPLS-TP expert.  However, the introductory text needs significant work 


to make it


easier for people who are not MPLS-TP experts to come to grips with the 


document.






The major issue with this document is that it appears to go against the 


current IETF view


that SNMP is not a satisfactory solution for configuring networks. The 


document has


effectively reiterated the RFC 3812 situation from 10 years ago when the 


IETF held its nose


and said that SNMP  was the only game in town even if security sucked. 


As I mention below, this was extensively discussed a year ago but I 


couldn't determine whether this draft was given


a special dispensation even though consensus seemed to be that writeable 


MIBs were


considered inappropriate.  If this is the case, it will be sufficient to 


adapt the end of s1.






AFAICS this draft has not had the 'grammar review' recommended by its AD 


about a year


ago and there are a number of areas in the object descriptions where 


language


improvements would be desirable in addition to notes given here. That is 


it still needs



the grammar review.



There are some more minor issues, particularly as regards the 


description of the types


of tunnel in s1, the discussion of the contents of the MIBs in s6 and 


possibly in regard to



the interaction with the standard interface table.


Major issues:

Support for configuration:


The issue of SNMPset (write) support was discussed at length in the 


context of


the MIB doctors' review of v-05 of this draft. The consensus at that 


time appeared


to be that provision of write support in new MIBs should be strongly 


discouraged.


I am unclear what the outcome of that discussion in the context of this 


draft was,


but it is clear that the draft is very much written from the point of 


using the MIB


as a configuration tool, especially in s9 (examples of usage). Whilst 


this technique


reflects the equivalent section is RFC 3813, that document was written 


over 10 years


ago and considerable effort has been devoted to providing alternative 


and more secure


ways of configuring networks in the intervening time. The body of the 


document has not



been altered to reflect the discussion that occurred.



"Lip service" is paid to the discouragement of the use of SNMPset by the 


addition of



para 3 of s1:



It is understood that SNMP SET is not used for MPLS configuration these
days, however the read-write and read-create option is still specified
for some objects as a way to provide the information model.


It is not clear to me why providing read-write or read-create options 


enhance the



MIB or are "a way to provide the information model".



I note that despite the extensive discussion of this topic by WG members 


and MIB specialists


back in December 2013, this issue was not flagged up in the Shepherd's 


write up.






If it has now been agreed that the configuration "flavour" is to be 


accepted as WG consensus


in spite of being contrary to current practice, it appears to me that 


the word "configuration"


should be removed from the last sentence of para 2 of s1 and the last 


para of s1 rewritten to



explain why write capabilities are used in a more convincing manner.

Minor issues:


Abstract/s1: Needs to be clear in both places that is is intended for 


MPLS-TP, this:


-- Abstract and s1: s/transport networks./MPLS networks conforming to 


the MPLS Transport Profile (MPLS-TP)./




s1: What is a Non-MPLS-TP (transport) network?



s1: The explanation of what the MIB extensions in this document actually 


do is not clear to the



general reader. I suggest replacing para 2 completely:

OLD:
The existing MPLS Traffic Engineering (TE) Management Information Base
(MIB) [RFC3812] and Generalized Multiprotocol Label Switching (GMPLS)
Traffic Engineering Management Information Base [RFC4802] do not support
the management of transport network requirements of Tunnel end points
with non-IP based identifiers and static bidirectional tunnels. This
document focuses on static bidirectional MIB modules that should be used
in conjunction with [RFC3812] and companion document [RFC3813] for MPLS
Transport Profile (MPLS-TP) path configuration and management.

NEW:


As described in the MPLS Traffic Engineering (TE) Management Information 


Base (MIB) definition [RFC3812], MPLS traffic engineering is concerned 


with the



creation and management of MPLS tunnels. This term is a shorthand for a


combination of one or one or explicitly routed LSPs (ERLSPs) linking an 


ingress


and an egress LSR. Several types of point-to-point MPLS tunnels may be 


constructed



between a pair of LSRs A and B:

- Unidirectional with a single LSP (say) from A to B.



- Associated bidirectional consisting of two separately routed ERLSPs, 


one linking


A to B and the other linking B to A. Together the pair provide a single 


logical



bidirectional transport path.



- Corouted bidirectional consisting of an associated bidirectional 


tunnel but with



the second ERLSP from B to A following the reverse of the path of the ERLSP
from A to B, in terms of both nodes and links.



Tunnels may be either statically configured by management action or 


dynamically created using



a LSP management protocol.



The existing MPLS TE MIB [RFC3812] and the Generalized Multiprotocol 


Label Switching (GMPLS) Traffic Engineering Management Information Base 


[RFC4802] address only a subset of the


combinations of statically and dynamically configured tunnel types, 


catering for statically


configured unidirectional tunnels together with dynamically configured 


unidirectional and


corouted bidirectional tunnels. They are alsorestricted to to end point 


LSRs identified



by IP addresses.



The MPLS-TP TE MIB defined in this document extends the MIB defined in 


[RFC3812] to cover


all six combinations (that is adding support for statically configured 


associated and


corouted bidirectional plus dynamically configured associated 


bidirectional tunnels). It also


extends support to end points that are identified other than with IP 


addresses.






This support is provided by a suite of four MIB modules that are to be 


used in conjunction


with the MIBS defined in [RFC3812] and the companion document [RFC3813] 


for MPLS



Transport Profile (MPLS-TP) TE path [configuration and]* management.

END NEW



* Note: Using the term 'configuration' is inconsistent with the 


discussion in para 3.



See Major Issues above



s5, bullet 1: s8 in RFC 3812 discusses the use of the Interface Table 


with MPLS. It should be



made clear here:


1. Whether, if the MPLS-TP Tunnel is treated as an interface, there is 


any difference in the usage


of the ifTable fields as compared with standard MPLS. In particular if a 


different interface type



should be applicable.


2. Are there any issues if all or (more especially) a subset of the 


tunnels are not treated as



interfaces



Row pointer usage: s9 of RFC 3812 considers Row Pointer usage - are 


there any differences or



additional considerations for these MIBs?



s6: Sections 6.1 to 6.4 are not MIBs (as indicated by the title and 


prologue) but MIB objects in


the MPLS-TE-EXT-STD-MIB MIB. Please reorganize s6 accordingly. Looking 


back at RFC3812, the


structure of the document in sections 5 and 6 appears to be more helpful 


to the new reader with a


summary of the four MIB modules in one section (expanded from ss6.5 - 


6.7) followed by notes on


the key MIB objects in each MIB as necessary. It would also be helpful 


to clarify where objects in


this MIB are expected to parallel those in the basic (RFC 3812) and note 


that they are indexed


equivalently (notably in the case of mplsTunnelTable and 


mplsTunnelExtTable).



Nits/editorial comments:


General: Consistent use of bi-directional or bidirectional: Please 


choose one and use it throughout.






General: The qualifier "sparse" is used incorrectly in several places 


(e.g., sparsely extended).


Presumably the intention is that the extensions are "slight" or 


"limited" . In most cases the term


can be deleted: The degree of extension will ultimately be in the eyes 


of the implementer!


(s5 - 2 cases, s6.4, s7 - 2 cases, s8, s9.1.6, s9.2.9, s9.3.6, s12 - 3 


cases)


General: The figures need number and captions. The numbers should be 


used to refer to the figures.




s4, para 1: s/unidirectional tunnel/unidirectional tunnels/

s4, para 1, last sentence: s/re-use/re-use and extend/

s4, para 2:
OLD:
retained in the same document, instead of a separate document.
NEW:
all defined in this document, rather than split over several documents.

s5, para 1: s/This document identifies/The MIBs in this document satisfy/



s5, para 2: s/The MIB module supports/The MIB modules, taken together, 


support/






s5, para 2: s/static and signaled/statically configured and dynamically 


signaled/




s5, bullet 4: s/sparsely extended/extended/

s9.1.6, s9.2.9, s9.3.6: s/a sparse augmentation/a limited augmentation/



s5, bullet 5: It would be helpful to explain how node identification 


differs from


standard MPLS to understand why this mapping is needed. There appears to 


be text in s6.1 that might help



but it is too late to make it easy to understand this section.



ss10-13: It is conventional to give the RFCs used as references in the 


docuement s/RFC 3812/[RFC3812]/ etc.






s14: This is a near duplicate of the security considerations in RFC 


3812. It might be easier to reference


that section and add a note that extra tables may provide further 


sensitive information.






A brief discussion of whether the non-IP case makes any difference would 


be useful.






s16: At the very least RFC 3811, RFC 3812 and RFC 3813 are normative. 


RFC 6923 probably is.



RFC 6370 and RFC 4802 may also be.