Re: AD Review of draft-ietf-rtgwg-lfa-manageability

[Alia Atlas <[e-mail]>]

Hi Stephane,

On Fri, Jun 12, 2015 at 8:55 AM, <[e-mail]> wrote:

>  Hi Alia,
>
>
>
> Many thanks for your review, I will address them shortly and publish a new
> version.
>
> Some comments inline.
>
>
Sounds good.


>
>
>
>
> Best Regards,
>
>
>
> Stephane
>
>
>
> *From:* rtgwg [mailto:[e-mail]] *On Behalf Of *Alia Atlas
> *Sent:* Thursday, June 04, 2015 23:44
> *To:* [e-mail]; [e-mail]
> *Subject:* AD Review of draft-ietf-rtgwg-lfa-manageability
>
>
>
> As is customary, I have done my AD Review of this draft.   Thank you for a
> clearly written and well thought out draft.
>
> I do have some minor concerns,  as below, but I am also letting this draft
> move to IETF Last Call while they are addressed.   I will need an updated
> draft by June 18, so the draft can go on the IESG telechat on June 25.
>
> Minor comments:
>
> 0)      This draft has 6 authors.  Please prune down to 5 or assign an
> editor or two.
>
> [SLI] Everyone listed worked hardly on the text as well as on
> specifications, I will put myself as editor to keep everyone J.
>
> We can talk about this.  Having 6 authors/editors is an exception that I
would have to approve.

>   1) In section 6.2.1, it says " When selecting the best alternate, the
> selection algorithm MUST
>       consider all available alternates (connected or tunnel).  Especially,
>       computation of PQ set ([I-D.ietf-rtgwg-remote-lfa]) SHOULD be
>       performed before best alternate selection."
>
>       Instead of "Especially" with a SHOULD - which implies that Remote
> LFA should always be run, could you change it to:  "For example with Remote
> LFA, computation of PQ set ...."?   I think the manageability concerns in
> this document are useful regardless of the fast-reroute technology and this
> is only a good example of an implementation ordering that is important.
>
> [SLI] Fixed.
>
>   2) In 6.2.4.1: " attributes from PLR to alternate path are retrieved
> from the
>       interface connected to the alternate."
>
>       There can be multiple interfaces.  The correct behavior (union or
>  evaluate once per different interface) should be clearly described.  The
> similar issue exists for the alternate path and in 6.2.4.2, but there may
> be more or less freedom about controlling which path is taken.
>
> [SLI] I need to discuss with my co authors on that.
>
Yes, I think this one is a non-trivial.  It's made more amusing by the
probability of multiple paths taken at downstream hops.  I can see being
conservative there but able to pick for the first hop.

  3) In Sec 6.2.6, "Maintain a preference system between alternates based
> on number of
>
>       SRLG violations : more violations = less preference."   The way that
> I've seen SRLGs used as a soft restriction is by giving each SRLG a value.
> Then one can prefer the lower sum.  This allows different consideration and
> valuation of the SRLGs.  Of course, this can fall back to each SRLG has a
> value of 1.   Could you please loosen the assumption here about equally
> valuing the SRLGs?  I'd prefer to see both alternatives allowed - but that
> is <no-hat>technical opinion</no-hat> whereas loosening the assumption is
> about not accidentally forcing more limited behavior and removing the
> ability to implement more sophisticated mechanisms.
>
> [SLI] Right, here is a new text proposal which is more open:
>
> “
>
> When SRLG protection is computed, and implementation SHOULD permit to :
>
>                                                 <list style="symbols">
>
>                                                 <t>Exclude alternates
> violating SRLG.</t>
>
>                                                 <t>Maintain a preference
> system between alternates based on SRLG violations. How the preference
> system is implemented is out of scope of this document but here are few
> examples :
>
>                                                 <list style="symbols">
>
>                                                 <t>Preference based on
> number of violation. In this case : the more violation = the less
> preferred.</t>
>
>                                                 <t>Preference based on
> violation cost. In this case, each SRLG violation has an associated cost.
> The lower violation cost sum is preferred.</t>
>
>                                                 </list>”
>
Looks good.

>  The path considerations mentioned in (2) still apply.
>
 4) In Sec 6.2.7, you might be interested in the link/node-attribute drafts
> that are being finished.
>
> [SLI] Could you give me the pointers of drafts you are thinking about ?
>

You have the ISIS one for node admin tags.  I was also thinking of
draft-ietf-ospf-node-admin-tag-02
<http://datatracker.ietf.org/doc/draft-ietf-ospf-node-admin-tag/>
and draft-ietf-ospf-prefix-link-attr-06
<http://datatracker.ietf.org/doc/draft-ietf-ospf-prefix-link-attr/>.  For
ISIS, it looks like the similar draft
only provides for prefix attributes and not link ones.

Regards,
Alia

>  5) In Sec 6.2.8: "The bandwidth criteria of the policy framework SHOULD
> work in two
>    ways"  Please expand to "at least two ways" - there are other
> strategies as well that might be reasonable and no standardization reason
> to rule them out.
>
> [SLI] Agree, fixed
>
> Nits:
>    a) Introduction needs to be the first section. Terminology can follow.
>
> [SLI] Fixed
>
>   b) Remote LFA reference needs updating to RFC 7490.  I think,  given
> some of the details in this draft,  that it should be a normative reference.
>
> [SLI] Fixed.
>
>
>
> Thanks for the good work,
> Alia
>
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