Re: [Idr] Benjamin Kaduk's No Objection on draft-ietf-idr-bgp-optimal-route-reflection-25: (with COMMENT)

[Benjamin Kaduk <[e-mail]>]

Hi Robert,

On Wed, Jun 16, 2021 at 08:38:39PM +0200, Robert Raszuk wrote:
> Hi Benjamin,
> 
> Many thx for your review.
> 
> Great catch on SHOULD vs MUST !  Changed.

Thanks!

> On the point regarding the Security Considerations  section 5 the
> inconsistent policies would only be of a problem in those networks which do
> not encapsulate packets in some way between ingress and egress. So to
> restate this the significant portion of Deployment Considerations would
> have to be repeated. Also while clearly a valid point in regards to routing
> correctness it is debatable if this is a security risk as such even if
> policy would be completely wrong between participating route reflectors.

Understood; it does not seem worth duplicating so much of the deployment
considerations just for this point.

> Regarding moving referencing of RFC7911 to normative let's observe that it
> may be required only in one specific deployment scenario of using multiple
> clusters in non encapsulating networks for IPv4/IPv6 AFs. It is clearly not
> required for other deployment models of BGP ORR. Therefore I am not sure if
> it deserves the elevated level of referencing in the document. But if the
> above use is a sufficient reason to treat it as normative reference I
> personally have no problem moving it.

I'm happy to leave this to the responsible AD; my comment stems from the
IESG statement at
https://www.ietf.org/about/groups/iesg/statements/normative-informative-references/
that points out that "even references that are relevant only for optional
protocol features must be classified as normative" (if they would otherwise
meet the criteria.  Only needed in some deployment scenarios is not quite
the same as being an optional feature, though, so I think there's still
some element of judgment needed.

> All other NITS were fixed. Thank you so much for help in spotting those
> unclear sentences.
> 
> I will be posting the next version shortly.

Sounds good, and thanks!

-Ben

> 
> 
> On Wed, Jun 16, 2021 at 6:19 PM Benjamin Kaduk via Datatracker <
> [e-mail]> wrote:
> 
> > Benjamin Kaduk has entered the following ballot position for
> > draft-ietf-idr-bgp-optimal-route-reflection-25: No Objection
> >
> > When responding, please keep the subject line intact and reply to all
> > email addresses included in the To and CC lines. (Feel free to cut this
> > introductory paragraph, however.)
> >
> >
> > Please refer to https://www.ietf.org/iesg/statement/discuss-criteria.html
> > for more information about DISCUSS and COMMENT positions.
> >
> >
> > The document, along with other ballot positions, can be found here:
> >
> > https://datatracker.ietf.org/doc/draft-ietf-idr-bgp-optimal-route-reflection/
> >
> >
> >
> > ----------------------------------------------------------------------
> > COMMENT:
> > ----------------------------------------------------------------------
> >
> > Thank you for this document; it gives a clear explanation of what is to
> > be done and why, and I basically only have nit-level comments, with the
> > exception of the first remark.
> >
> > Section 4
> >
> >    This solution can be deployed in traditional hop-by-hop forwarding
> >    networks as well as in end-to-end tunneled environments.  In networks
> >    where there are multiple route reflectors and hop-by-hop forwarding
> >    without encapsulation, such optimizations SHOULD be consistently
> >    enabled on all route reflectors.  Otherwise, clients may receive an
> >    inconsistent view of the network, in turn leading to intra-domain
> >    forwarding loops.
> >
> > The scope of "forwarding loops" as a potential problem makes me wonder
> > if the "SHOULD"-level requirement for this avoidance mechanism is the
> > right choice.
> >
> > Section 5
> >
> > Thank you for accepting the wording suggestion from Roman; it's a good
> > improvement.
> >
> > I might consider reiterating that there are risks if multiple route
> > reflectors are present but using different policy/procedures, though the
> > earlier discussion may suffice.
> >
> > Section 9.2
> >
> > Whether RFC 7911 should be normative or informative seems potentially
> > subject to debate, if deployment of add-path is required in order for
> > correct operation of optimal route reflectors.
> >
> > NITS
> >
> >                                                     This ability enables
> >    the route reflector to send to a given set of clients routes with
> >    shortest distance to the next hops from the position of the selected
> >    IGP location.  [...]
> >
> > This feels a bit like a garden-path sentence that makes the reader
> > backtrack to fix their parse tree; commas around "to a given set of
> > clients" might help but a more substantive restructuring might be
> > preferred.
> >
> >                   This provides for freedom of route reflector physical
> >    location, and allows transient or permanent migration of this network
> >    control plane function to an arbitrary location.
> >
> > Pedantically, such a migration seems like it would always have been
> > possible, just with a potentially significant impact on performance and
> > route quality; I'd suggest appending a phrase such as "with negligible
> > impact on performance".
> >
> >    The choice of specific granularity (route reflector, set of clients,
> >    or client) is configured by the network operator.  An implementation
> >    is considered compliant with this document if it supports at least
> >    one listed grouping of IGP location.
> >
> > It's not entirely clear to me how a "listed grouping of IGP location"
> > maps to the previous text.
> >
> > Section 3.2
> >
> >    If the required routing optimization is limited to the IGP cost to
> >    the BGP Next-Hop, only step e) and below as defined [RFC4271] section
> >    9.1.2.2, needs to be run multiple times.
> >
> > I think maybe s/and below/and subsequent steps/, and s/as defined/as
> > defined in/.
> >
> > Section 4
> >
> >    route reflectors.  More specifically, the choice of BGP path factors
> >    in either the IGP cost between the client and the NEXT_HOP (rather
> >
> > I suggest s/factors in/takes into account/, since "factors in" is
> > something of a colloquialism.
> >
> >    Modifying the IGP location of BGP ORR does not interfere with
> >    policies enforced before IGP tie-breaking (step e) in the BGP
> >    Decision Process Route.
> >
> > I think "step e" has to be scoped to §9.1.2.2 of RFC 4271.
> >
> >                                                           Similarly, if
> >    an IGP location is selected for the whole routing instance, the
> >    lowest precision is achieved, but the performance impact is minimal
> >    (both should be equal to the [RFC4456] ones).  [...]
> >
> > The phrasing in the parenthetical seems surpising to me -- what does
> > "both" refer to?  I can only see the one "performance of the
> > single-IGP-location-for-the-whole-routing-instance" situation, which of
> > course should have equivalent performance to the stock RFC 4456 case.
> >
> > Section 5
> >
> >    This extension provides a new metric value using additional
> >    information for computing routes for BGP router reflectors.  While
> >
> > s/router/route/
> >
> >
> >
> >