Re: [mpls] George can yu look at this - Re: end of WGLC, RE: working group last call for draft-ietf-mpls-lsp-ping-reply-mode-simple-01

[Nobo Akiya <[e-mail]>]

Hi Adrian, Tom, Loa,

This extension is currently structured such that it allows for backwards
compatibility (i.e., transit LSR not supporting this mechanism will not
return "malformed request" ... because the TLV is optional).

The result is that this mechanism becomes a best effort mechanism, and we
will not get the full benefit until all LSRs along the LSP (and other LSRs
which could falsely receive the echo request) implements this extension.

One way to allow the initiator LSR to determine whether or not the
responder LSR understood this TLV, and still keeping the backwards
compatibility, is that we keep the Reply Mode Order TLV as an optional TLV,
but require (i.e., MUST) the responder LSR understanding this TLV to
include the Reply Mode Order TLV in the echo reply, potentially with result
of parsing/handling that TLV.

However, that's probably not the path we want to go, as all (or most)
optional TLVs will have to do something similar (i.e., include the same TLV
in the echo reply). This will quickly result in echo reply packet bloat ...
we should prevent that as echo reply usually tends to include more
information (ILS, DSMAP/DDMAP per nexthop, multipath Sub-TLVs per nexthop,
etc).

To me, the right way to solve this is to create a capability TLV that
mandates the reponder LSR to return which features it supports in bitmaps
or something very compact. But this can be done in a separate effort/draft.

In short, my preference for this document is to go as is (after
incorporating comments from Tom).

Thanks!

-Nobo

On Thu, Apr 23, 2015 at 4:38 PM, Adrian Farrel <[e-mail]> wrote:

> Thanks Loa,
>
> You captured it. The edge cases need to be nailed down.
>
> Personally I have no particular preference for where it is nailed, but I
> don't
> want it flapping in the breeze.
>
> A
>
> > -----Original Message-----
> > From: mpls [mailto:[e-mail]] On Behalf Of Loa Andersson
> > Sent: 23 April 2015 13:59
> > To: t.petch; Nobo Akiya
> > Cc: Ross Callon; mpls; [e-mail];
> draft-ietf-mpls-lsp-ping-reply-
> > [e-mail]
> > Subject: [mpls] George can yu look at this - Re: end of WGLC, RE: working
> group
> > last call for draft-ietf-mpls-lsp-ping-reply-mode-simple-01
> >
> > Tom,
> >
> > The question you and Adrian asks is what to do if the Reply Mode
> > Order TLV is missing.
> >
> > There is something fishy here, I'd like George to look at this.
> >
> > The LSP Ping design says that TLVs from this range may be silentsly
> > dropped, my take is that we don't need to specify anything more
> > than that.
> >
> > Now, we say that it MUST be present, and after thinking around a bit
> > I wonder if the TLV should be assigned from the mandatory range instead?
> >
> > Or if the MUST be present means that the message will be malformed if
> > it is not there, and the message should be discarded.
> >
> > OK - now I'm confused.
> >
> > /Loa
> >
> > On 2015-04-23 13:02, t.petch wrote:
> > > ---- Original Message -----
> > > From: "Loa Andersson" <[e-mail]>
> > > Sent: Wednesday, April 22, 2015 2:15 PM
> > >
> > >> Tom,
> > >>
> > >> On 2015-04-20 00:07, Nobo Akiya wrote:
> > >>>      <tp>
> > >>>
> > >>>      Yes but ... I think that it is a change of meaning.  Is is
> > > enough just
> > >>>      to ignore the TLV or should the whole PDU be discarded?  I find
> > > it
> > >>>      difficult to know but don't feel strongly about that choice so
> > > will go
> > >>>      with what you suggest.
> > >>>
> > >>>      </tp>
> > >>
> > >> So I don't misunderstand what you are saying. It seems to me like the
> > >> comments made by Adrian and you actually requires a "change of
> > > meaning",
> > >> that is kind of essence of a "comment", right?
> > >>
> > >> As for what to do with if the TLV is not recognized, it is
> > >> intentionally requested from a space where it can be silently dropped
> > >> (i.e. "ignored").
> > >>
> > >>      The new TLV Type value should be assigned from the range
> > >>      (32768-49161) specified in [RFC4379] section 3 that allows the
> TLV
> > >>      type to be silently dropped if not recognized.
> > >>
> > >>        Type   Meaning                            Reference
> > >>        ----   -------                            ---------
> > >>        TBD1   Reply Mode Order TLV               this document
> > >>
> > >> What is it that I miss?
> > >
> > > Nothing serious.  My initial thought was to echo Adrian, that, at least
> > > in this context, there should be an indication what to do if a MUST or
> > > SHOULD was violated without just then having a clear sense of what it
> > > should be instead.
> > >
> > > The I-D did require (MUST) one entry in the TLV and wanted (SHOULD)
> > > more.  Adding what to do if that did not happen I was seeing as
> > > clarification.  I then read Nobo as proposing going a bit further
> saying
> > > requires (MUST) one or more.  Which might lead to boxes taking a
> > > simplistic approach and always putting in the new TLV with a single
> > > entry and ignoring the traditional TLV.  Not a problem just a change
> > > from what others might think that they have consented to.
> > >
> > > On the question of what to do when the rules are violated, again I did
> > > not initially think of what the action should be.  On reflection, I am
> > > still unsure.  I understand that the Reply Mode Order TLV  is optional
> > > and so can be ignored when not understood; that's fine.  But if it is
> > > understood and can be seen to be defective, should the box with that
> > > knowledge discard just that TLV and accept the remainder of the
> message?
> > > Or should it argue that if this TLV is defective, then likely the rest
> > > is as well and should be ignored?  I am unsure.
> > >
> > > If there is scope for a breach of security, or taking a hit in
> > > performance, then ignore is the right policy. If the requirement is to
> > > get as much data as possible from a failing network, then use it is the
> > > right policy.  As long as the I-D is clear, I am not too fussed which
> > > way it goes.  I am content with the changes that Nobo has proposed.
> > >
> > > Tom Petch
> > >
> > >> /Loa
> > >>
> > >> --
> > >>
> > >>
> > >> Loa Andersson                        email: [e-mail]
> > >> Senior MPLS Expert                          [e-mail]
> > >> Huawei Technologies (consultant)     phone: [phone]
> > >
> >
> > --
> >
> >
> > Loa Andersson                        email: [e-mail]
> > Senior MPLS Expert                          [e-mail]
> > Huawei Technologies (consultant)     phone: [phone]
> >
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