Re: [Lsr] [yang-doctors] Yangdoctors last call review of draft-ietf-isis-yang-is-is-cfg-29

[Andy Bierman <[e-mail]>]

On Thu, Jan 10, 2019 at 4:42 AM Acee Lindem (acee) <[e-mail]> wrote:

> Hi Andy,
>
> On 1/10/19, 7:38 AM, "Andy Bierman" <[e-mail]> wrote:
>
>     On Thu, Jan 10, 2019 at 12:34 AM <[e-mail]>
> wrote:
>
>     > Hi Andy,
>     >
>     >
>     >
>     > What I’m still not catching is the difference you make between
> having a
>     > description statement telling :” A server MUST accept a string up to
> 64
>     > characters in length” and a type string with length “0..64” ?
>     >
>     > There is probably something that I’m missing here.
>     >
>     >
>     >
>
>     A server MAY accept a string longer than 64 characters.
>     A range 0..64 means a server MUST NOT accept a string longer than 64
>     Characters
>
> I don't think we should set the string range unless the range in specified
> in the protocol RFCs. In some cases, it may be beneficial to provide
> guidance in the description. I believe this is similar to Juergen's
> position.
>
>
Agreed -- that is a good guideline for protocol related strings.
But what about admin strings?

NETCONF/YANG does not have a data type like SnmpAdminString
(which has a range of 0..255 octets)

Some of us implement servers using the theory that the NMS knows
what it's doing and servers do what they are told.  So if the client
configured a 1M byte admin string the server would try to accept it instead
of putting an arbitrary limit (because there is no YANG limit).

I prefer the SnmpAdminString approach because the client knows what
every compliant server will accept.  But YANG models just use plain string
and only regression test tools ask for 1M byte admin strings. IMO, this has
not been
a problem in real deployments. We should continue to use plain "string" for
admin strings.


Thanks,
> Acee
>

Andy


>
>
>
>     > Brgds,
>     >
>     >
>     >
>
>
>     Andy
>
>
>     > *From:* Andy Bierman [mailto:[e-mail]]
>     > *Sent:* Wednesday, January 09, 2019 18:06
>     > *To:* Juergen Schoenwaelder; LITKOWSKI Stephane OBS/OINIS; tom petch;
>     > Ebben Aries; [e-mail];
>     > [e-mail]; [e-mail]
>     > *Subject:* Re: [yang-doctors] [Lsr] Yangdoctors last call review of
>     > draft-ietf-isis-yang-is-is-cfg-29
>     >
>     >
>     >
>     > Hi,
>     >
>     >
>     >
>     > I agree with Juergen.
>     >
>     > The protocol has a "too-big" error is the server will not accept a
> big
>     > string.
>     >
>     > There should not be a false choice between an arbitrary maximum and
>     > "terabytes".
>     >
>     >
>     >
>     > You cannot use a range-stmt to specify the minimum required length
> that
>     > must be supported.
>     >
>     > length "3..max" does not allow strings of length 0 - 2.
>     >
>     >
>     >
>     > The description-stmt can have "A server MUST accept a string up to 64
>     > characters in length"
>     >
>     > which lets the client choose a length from 0 to 64, and this will
> work on
>     > all server implementations.
>     >
>     >
>     >
>     > Andy
>     >
>     >
>     >
>     >
>     >
>     > On Wed, Jan 9, 2019 at 5:10 AM Juergen Schoenwaelder <
>     > [e-mail]> wrote:
>     >
>     > Hi,
>     >
>     > please see my other email about the distinction I make between a hard
>     > length restriction and the minimum length expected to be supported.
> I
>     > wonder how you can sensibly pick a limit for things like
> non-best-reason:
>     >
>     >         leaf non-best-reason {
>     >           type string;
>     >           description
>     >             "Information field to describe why the alternate
>     >              is not best.";
>     >         }
>     >
>     > You are simply creating an arbitrary restriction. And humble server
> is
>     > not likely to send you an jpg image (and a bogus server will do so
>     > anyway). (There are other similar objects.)
>     >
>     > Since I am searching for 'type string', I wonder whether these are
>     > clear enough definitions.
>     >
>     >         leaf prefix {
>     >           type string;
>     >           description
>     >             "Protected prefix.";
>     >         }
>     >         leaf alternate {
>     >           type string;
>     >           description
>     >             "Alternate nexthop for the prefix.";
>     >         }
>     >
>     > What is the (canonical) format of the allowed values? (There are
> more of
>     > these.)
>     >
>     > /js
>     >
>     > On Wed, Jan 09, 2019 at 12:52:07PM +0000,
> [e-mail]
>     > wrote:
>     > > Hi Tom,
>     > >
>     > > If you agree, I will set a length restriction on each string (ops
> and
>     > cfg). It looks clearer for me rather than setting it in the
> description.
>     > >
>     > > For the references, I'm working on it.
>     > >
>     > > Brgds,
>     > >
>     > >
>     > > -----Original Message-----
>     > > From: tom petch [mailto:[e-mail]]
>     > > Sent: Wednesday, January 09, 2019 12:38
>     > > To: LITKOWSKI Stephane OBS/OINIS; Ebben Aries;
> [e-mail]
>     > > Cc: [e-mail]; [e-mail]
>     > > Subject: Re: [Lsr] Yangdoctors last call review of
>     > draft-ietf-isis-yang-is-is-cfg-29
>     > >
>     > > Stephane
>     > >
>     > > Thanks for persisting.
>     > >
>     > > On string lengths, I take your point about no user input to
> Operational
>     > > State; there, my concern is more about giving guidance to
> implementors
>     > > as to what they should cater for - as I said, this has been a
> topic of
>     > > lively discussion in other WG.  Even before that, whenever I see a
>     > > string, I think is there an implicit length restriction and if not,
>     > > should there be an explicit one which, as Juergen suggested, could
> be in
>     > > the description clause.  My experience is that those working with
>     > > networks think about size, about length; those coming from
> applications
>     > > tend to think 'What is a few terabytes between friends?' and are
> unaware
>     > > that sizes that may be commonplace in servers and associated
> storage can
>     > > create difficulties over a network.  Whatever, I leave this one up
> to
>     > > you.
>     > >
>     > > On references, I would like a change; you say this information is
> in the
>     > > base ISO spec.  Well, yes, to me that means that it should be a
>     > > Normative Reference.  I could not understand the description of
> e.g.
>     > > 'i/e' and needed to look it up but seemingly cannot do so with the
>     > > listed references of the I-D.  Note that RFC such as RFC5305 and
> RFC6119
>     > > do reference International Standard 10589 and I think that this one
>     > > should too, perhaps in s.2.7 and s.5.
>     > >
>     > > Tom Petch
>     > >
>     > > ----- Original Message -----
>     > > From: <[e-mail]>
>     > > Sent: Wednesday, January 09, 2019 9:18 AM
>     > >
>     > > Hi Tom,
>     > >
>     > > Please find inline answers.
>     > >
>     > >
>     > > -----Original Message-----
>     > > From: tom petch [mailto:[e-mail]]
>     > > Sent: Tuesday, January 08, 2019 18:45
>     > >
>     > > Ok.  Top-posting the ones that are not 'ok':
>     > >
>     > > I said that I thought that LSP did not need expanding on first use
> and
>     > > then checked the RFC Editor list to find that it is not one they
> regard
>     > > as well-known and that LSR protocols use it differently to others,
> so I
>     > > suggest expanding LSP on first use.
>     > >
>     > > [SLI] Already done for the next version.
>     > >
>     > > On lengths of text messages, perhaps I am too sensitive to buffer
>     > > overrun attacks and the like and so want a maximum on many things
> (and
>     > > then people attach a friendly, 20Mbyte photo to their e-mail at
>     > > Christmas and
>     > > wonder why their ESP rejects the message so I do not congratulate
> them
>     > > on the latest addition to the family:-).  The IDR WG had a lively
>     > > discussion about maximum message lengths in 2017 and that has also
>     > > stayed in my mind.  I have seen the comments on this by Juergen and
>     > > Lada; perhaps as Juergen intimates, something in the Description
> would
>     > > help; and while the server may not be rogue, it may not have a
> perfect
>     > > implementation.
>     > >
>     > > [SLI] What I need to understand from your comment on string length
>     > > enforcement is if it applies to operational state or just config
> states
>     > > ? I do not see any issue of not enforcing the operational state as
> there
>     > > is no input from the user there and so no attack vector, this is
> purely
>     > > internal to the implementation. For config statements, it makes
> sense as
>     > > there is an input from the user that can be anything.
>     > >
>     > >
>     > > On the length of password, I saw a Security AD wanting
> clarification on
>     > > this not too long ago so you may see this comment again from one
> such .
>     > > Likewise, MD5 tends to be a red flag although I see it appears in
> bgp
>     > > yang.
>     > >
>     > > I like the sort of detail in ippm-twamp-yang, on algorithms,
> entropy and
>     > > such like (although I have not seen a review by Security
> AD/directorate
>     > > of that).
>     > >
>     > > But I am left confused as to exactly what the cited object is
> doing.
>     > > Yes, TLV10 provides authentication for any PDU, but what are the
> fields
>     > > in the YANG module doing?  Is
>     > >        leaf authentication-type {
>     > > the first octet of TLV10?  Is
>     > >       leaf authentication-key {
>     > > the rest of TLV10?  And where is this 'presented' as the YANG
> module
>     > > says?  Are you thinking of a YANG client presenting the field to a
> user
>     > > at a terminal, one router presenting it to another, or what?
>     > >
>     > > I am using RFC5310 as my source for TLV10 and wondering why that
> is not
>     > > a Normative Reference for this I-D
>     > >
>     > > [SLI] TLV 10 is defined in the base ISO spec of IS-IS. RFC5310
> just adds
>     > > the crypto auth as new types.
>     > > The authentication-type is the first byte of the TLV (called
>     > > Authentication Type as well).
>     > > The authentication-key cannot be mapped directly to the
>     > > authentication-value field. This is the case for ClearText password
>     > > authtype but not crypto which adds a keyID in front of the
>     > > authentication data.
>     > >
>     > >
>     > > On the I/E bit, the question is, which standard?  I have 30
> Normative
>     > > references to choose from.   I found up/down in RFC5305, but only
> by
>     > > accident, and I have not found i/e yet so a reference would be
> good.
>     > >
>     > > [SLI] I/E bit is part of the base ISO spec of IS-IS and relevant
> for
>     > > "legacy advertisements" of prefix and links. By the way, after
> checking,
>     > > the position of the i-e leaf is currently wrong and needs to be
> within
>     > > the metric (default, delay...). I will fix this.
>     > >
>     > >
>     > > Tom Petch
>     > >
>     > > ----- Original Message -----
>     > > From: [e-mail]
>     > > Sent: Monday, January 07, 2019 9:22 AM
>     > >
>     > > Hi Tom,
>     > >
>     > > Thanks for your comments.
>     > > I wish you an happy new year !
>     > >
>     > > Please find inline comments.
>     > >
>     > > Brgds,
>     > >
>     > > -----Original Message-----
>     > > From: tom petch [mailto:[e-mail]]
>     > > Sent: Wednesday, January 02, 2019 12:17
>     > >
>     > > Here are the rest of my comments on -29 with a slight tweak to the
>     > > subject line.  I would regard most of these (but not the first
> two) as
>     > > non-discussable, ie I won't complain if you disagree:-)
>     > >
>     > > RFC1195 is in the YANG module but not the references of the I-D
>     > > [SLI] Will fix it
>     > >
>     > > RFC5029 is in the YANG module but not the references of the I-D
>     > > [SLI] Will fix it
>     > >
>     > > PSNPs, CSNPs
>     > > [SLI] Will fix it
>     > >
>     > > expand on first use - LSP I think ok
>     > >
>     > >         leaf best {           type boolean;
>     > > what is true and what false?  I can guess from the English
> semantics of
>     > > the name but would rather not guess.
>     > > [SLI] Will fix it
>     > > To replace the current description which is : ""Indicates if the
>     > > alternate is the preferred."", do you prefer: "Set to true when the
>     > > alternate is preferred, set to false otherwise" ?
>     > >
>     > >
>     > >         leaf non-best-reason {          type string;
>     > > suggest a maximum length, perhaps 127 or 255 ( unless you expect
>     > > screenshots or packet traces to be attached).  As it stands, you
> could
>     > > validly receive
>     > > a length of 18446744073709551615.
>     > > [SLI] Agree, will fix it
>     > >
>     > > You have a mixture of
>     > > System-id system-id System id System ID System Id system id system
> ID
>     > > suggest consistency; system-id wfm
>     > > [SLI] Will fix it
>     > >
>     > > You have a mixture of
>     > > lsp-id LSPID LSP ID
>     > > here, perhaps lsp-id for the names and LSP ID in the text
>     > > [SLI] Will fix it
>     > >
>     > >       case password {        leaf key {           type string;
>     > > perhaps better with a minimum length
>     > > [SLI] I agree that it could make sense but is it really something
> that
>     > > we should impose ?
>     > >
>     > >
>     > >         leaf i-e {          type boolean;
>     > > what is true and what false?  here I am reluctant even to guess
>     > > [SLI] This is coming from the standard, is it really worth
> repeating it
>     > > ? Same for up/down bit.
>     > >
>     > >
>     > > /"Authentication keyto/  "Authentication key to/
>     > >
>     > > "     the authentication key MUST NOT be presented in"
>     > > RFC2119 language means that RFC2119 boilerplate should be in the
> YANG
>     > > module (but without the [..] ie the reference must be plain text
> not an
>     > > anchor).
>     > >
>     > > [SLI] You are right, it is missing.
>     > >
>     > >
>     > >  It is recommended to use an MD5
>     > >            hash to present the authentication-key.";
>     > > Mmm I think that this may be a red flag to security AD or
> directorate as
>     > > being too vague as well as MD5 too weak; and I think this should be
>     > > explicitly called out in Security Considerations.
>     > >
>     > > [SLI] I agree that there is a point to discuss here. The fact is
> that we
>     > > must not retrieve passwords in clear text. Maybe it is something
> with a
>     > > wider scope than IS-IS. How do the other models deal with passwords
>     > > retrieved through "get" or "get-config" ?
>     > >
>     > >
>     > >       list level-db {        key level;        leaf level {
>     > > A common convention is for a list of leaf thing to be named things
> i.e.
>     > >       list levels {         key level;        leaf level {
>     > >
>     > > [SLI] ack
>     > >
>     > >   rpc clear-adjacency {
>     > >           "Name of the IS-IS protocol instance whose IS-IS
>     > >            information is being queried.
>     > > queried or cleared?
>     > > [SLI] "cleared"
>     > >
>     > > Tom Petch
>     > >
>     > >
>     > > ----- Original Message -----
>     > > From: "tom petch" <[e-mail]>
>     > > Sent: Monday, December 31, 2018 6:21 PM
>     > >
>     > >
>     > > > Stephane
>     > > >
>     > > > A new and different comment.
>     > > >
>     > > >   grouping neighbor-gmpls-extensions {
>     > > >
>     > > > has a text reference to RFC5307 which does not appear in the
>     > > references
>     > > > for the I-D.  However, before adding it, I would like to know
> why it
>     > > is
>     > > > a good reference for switching capabilities (which is part of
> this
>     > > > grouping).  I think that the reference for switching capabilities
>     > > should
>     > > > be RFC7074 (which this I-D does not currently reference and
> should
>     > > IMO).
>     > > >
>     > > > And that begs the  question, why is switching-capability an
>     > > unrestricted
>     > > > uint8 when only 12 values are valid and three are deprecated?
>     > > >
>     > > > So why not use
>     > > >
>     > > > draft-ietf-teas-yang-te-types?
>     > > >
>     > > > I have a number of additional comments on cfg-29 but this is the
> one
>     > > > that may take some discussion.
>     > > >
>     > > > Tom Petch
>     > > >
>     > > >
>     > > > ----- Original Message -----
>     > > > From: <[e-mail]>
>     > > >
>     > > > Hi Tom,
>     > > >
>     > > > Thanks for your comments. I will fix them asap.
>     > > > Regarding:
>     > > > " Line length is within the RFC limit but the effect is to
> spread many
>     > > > of the description clauses over multiple lines with indentation
> of 56
>     > > > characters, not user friendly e.g.
>     > > >                                         description
>     > > >                                                 "List of max LSP
>     > > > bandwidths for different
>     > > >                                                  priorities.";
>     > > > "
>     > > > What's your suggestion on this one ?
>     > > >
>     > > > Brgds,
>     > > >
>     > > > -----Original Message-----
>     > > > From: tom petch [mailto:[e-mail]]
>     > > > Sent: Tuesday, November 27, 2018 12:11
>     > > > Subject: Re: [Lsr] Yangdoctors last call review of
>     > > > draft-ietf-isis-yang-isis-cfg-24
>     > > >
>     > > > Some quirks in-25
>     > > >
>     > > > I see lots of YANG reference statements - good - but no mention
> of
>     > > them
>     > > > in the I-D references - not so good.  My list is
>     > > >
>     > > > 5130
>     > > > 5305
>     > > > 5306
>     > > > 5880
>     > > > 5881
>     > > > 6119
>     > > > 6232
>     > > > 7794
>     > > > 7810
>     > > > 7917
>     > > > 8405
>     > > >
>     > > > Also perhaps
>     > > > OLD
>     > > >     reference "RFC XXXX - YANG Data Model for Bidirectional
>     > > >                Forwarding Detection (BFD).Please replace YYYY
> with
>     > > >
> published RFC
>     > > > number for draft-ietf-bfd-yang.";
>     > > >
>     > > > NEW
>     > > >     reference "RFC YYYY - YANG Data Model for Bidirectional
>     > > >                Forwarding Detection (BFD).
>     > > >
>     > > > -- Note to RFC Editor Please replace YYYY with published RFC
>     > > > number for draft-ietf-bfd-yang.";
>     > > >
>     > > > OLD
>     > > >       reference "draft-ietf-bfd-yang-xx.txt:
>     > > >                  YANG Data Model for Bidirectional Forwarding
>     > > >                  Detection (BFD)";
>     > > > NEW
>     > > >     reference "RFC YYYY - YANG Data Model for Bidirectional
>     > > >                Forwarding Detection (BFD).
>     > > >
>     > > > -- Note to RFC Editor Please replace YYYY with published RFC
>     > > > number for draft-ietf-bfd-yang.";
>     > > >
>     > > >
>     > > > Line length is within the RFC limit but the effect is to spread
> many
>     > > of
>     > > > the description clauses over multiple lines with indentation of
> 56
>     > > > characters, not user friendly
>     > > > e.g.
>     > > >                                         description
>     > > >                                                 "List of max LSP
>     > > > bandwidths for different
>     > > >                                                  priorities.";
>     > > >
>     > > >
>     > > > Acknowledgements is TBD. I note that the editor list of the YANG
>     > > module
>     > > > is somewhat longer than the editor list of the I-D.
>     > > >
>     > > > I note that the augmentation of interfaces seems to have no
>     > > conditional
>     > > > and so will augment all interfaces. I think that this is a
> generic
>     > > issue
>     > > > but do not see it being addressed anywhere.
>     > > >
>     > > > In a similar vein, you are defining MPLS objects and I am unclear
>     > > > whether or not those should be conditional, or part of the MPLS
> YANG
>     > > > modules or both (copying Tarek for this)
>     > > >
>     > > > Tom Petch
>     > > >
>     > > > ----- Original Message -----
>     > > > From: "Ebben Aries" <[e-mail]>
>     > > > Sent: Tuesday, October 23, 2018 12:45 AM
>     > > >
>     > > > > Reviewer: Ebben Aries
>     > > > > Review result: On the Right Track
>     > > > >
>     > > > > 1 module in this draft:
>     > > > > - [e-mail]
>     > > > >
>     > > > > No YANG compiler errors or warnings (from pyang 1.7.5 and
> yanglint
>     > > > 0.16.54)
>     > > > >
>     > > > > "ietf-isis@2018-08-09" module is compatible with the NMDA
>     > > > architecture.
>     > > > >
>     > > > > Module [e-mail]:
>     > > > > - Both the description and the draft name reference that this
> module
>     > > > is
>     > > > >   specific to configuration but contains operational state
> nodes in
>     > > > addition
>     > > > >   to RPCs and notifications.  Any wording suggesting this is
> only
>     > > > >   configuration should be changed
>     > > > > - Module description must contain most recent copyright notice
> per
>     > > > >
>     > > >
>     > >
> https://tools.ietf.org/html/draft-ietf-netmod-rfc6087bis-20#section-3.1
>     > > > > - Module description reads "common across all of the vendor
>     > > > implementations".
>     > > > >   I don't think this needs to be called out as such as that is
> the
>     > > > overall
>     > > > >   intention of *all* IETF models
>     > > > > - This module contains '22' features (and the respective OSPF
> module
>     > > > currently
>     > > > >   contains '26').  While it is understood the purpose of these
>     > > > features in the
>     > > > >   module, take precaution as to complexity for clients if they
> need
>     > > to
>     > > > >   understand >= quantity of features per module in use on a
>     > > > >   network-element.  We are going to end up w/ feature
> explosion to
>     > > > convey
>     > > > >   *all* possible features of each network-element leading to
>     > > > divergence back
>     > > > >   towards native models at the end of the day.  A large amount
> of
>     > > > these
>     > > > >   feature names could be defined within a more global namespace
>     > > (e.g.
>     > > > nsr) but
>     > > > >   this gives us a granular yet cumbersome approach (e.g.
> feature
>     > > > isis:nsr,
>     > > > >   ospf:nsr, etc..)
>     > > > > - RPC 'clear-adjacency' does not have any input leaf that
> covers
>     > > > clearing a
>     > > > >   specific neighbor/adjacency (See comments below as well
> regarding
>     > > > RPC
>     > > > >   alignment w/ the OSPF model)
>     > > > > - RPC 'clear-adjacency' has an input node of 'interface'
> however
>     > > this
>     > > > is just
>     > > > >   a string type.  Is there any reason this is not a
>     > > > leafref/if:interface-ref
>     > > > >   (much like in the OSPF model)
>     > > > > - Child nodes within a container or list SHOULD NOT replicate
> the
>     > > > parent
>     > > > >   identifier per
>     > > > >
>     > > >
>     > >
> https://tools.ietf.org/html/draft-ietf-netmod-rfc6087bis-20#section-4.3
>
>