Hi Elwyn,
Thanks for the review and comments.
Please find the responses inline.
On Dec 11, 2014, at 10:36 AM, Elwyn Davies <[email protected]> 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-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.
This MIB is intended to be used for MPLS-TP tunnels and is done by the way of
extending existing MPLS-TE MIB. The assumption is that reader is already aware
of MPLS-TP. Hence we didn’t provide a primer for MPLS-TP in this MIB and I am
not sure if it is the right place either.
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.
We have deliberated over this topic for more than two years and after multiple
discussions along with Routing AD and OPS AD, we decided to go forward with the
writable objects for this MIB. Additionally we added a small paragraph at the
end of s1, as recommended, the reason for doing so.
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.
We could take help of English reviewers and request WG chairs to help us out in
this regard.
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.
Whether SNMP write should exist or not discussion is not within the scope of
this document. Whether this MIB should support writable MIB objects was
discussed and the conclusion was yes. The text at end of s1 was added as
recommended by AD’s. On the contrary, if this MIB were to change the way
RFC3813 is to implemented/interpreted along with the MIB i.e. from writable for
TE but read-only for non MPLS-TE tunnels, then it should be documented.
"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.
As noted above, the write option was retained after discussing at length, both
at the WG sessions and over emails. The statement in last part of s1 was added
as per the advice we received to move forward with the writable objects [ref:
email from OPS AD dated Mar 11 on MPLS mailing list]. The main reason for
writable objects, is because the MPLS-TE had writable objects and MPLS-TP
extensions leverage this existing MIB and also few vendors have implemented
them.
Having said that, we are open to any suggested text, in addition to the one,
which you already did below, in regards to ‘writable’ objects.
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?
MPLS-TE and other MPLS networks which is not constrained by transport
requirements. Assuming some new tunnel type comes up into the future like
bi-directional TE. :D
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.
what is ‘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
Thank you. Will go through the text again and replace as suggested.
* 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
Haven’t come across any different types as such. Do you see any specific type
which is of contrary to RFC 3812, that MPLS-TP defines? Will ask my co-authors
as well.
Row pointer usage: s9 of RFC 3812 considers Row Pointer usage - are there any
differences or
additional considerations for these MIBs?
None that we are aware off.
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:
Nod.
General: Consistent use of bi-directional or bidirectional: Please choose one
and use it throughout.
Nod.
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.
Will review and edit as suggested.
s4, para 1: s/unidirectional tunnel/unidirectional tunnels/
Nod.
s4, para 1, last sentence: s/re-use/re-use and extend/
Nod.
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/
Nod for all the above.
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.
Will add reference to s6.1.
ss10-13: It is conventional to give the RFCs used as references in the
docuement s/RFC 3812/[RFC3812]/ etc.
Nod.
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.
Nod.
A brief discussion of whether the non-IP case makes any difference would be
useful.
I do not think there is a difference as such. We have provided example for
non-ip case anyway.
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.
Nod.
thanks again
-sam
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