Re: [Lsr] Benjamin Kaduk's Discuss on draft-ietf-isis-mpls-elc-12: (with DISCUSS and COMMENT)

Alvaro Retana <aretana.ietf@gmail.com> Tue, 26 May 2020 15:03 UTC

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From: Alvaro Retana <aretana.ietf@gmail.com>
In-Reply-To: <88a5c560-cb61-78c2-3733-931ffe529b6b@cisco.com>
References: <158992828112.6026.1646593855480055081@ietfa.amsl.com> <1242ad52-bb48-8526-b65b-d413e0cd9e25@cisco.com> <20200521193856.GJ58497@kduck.mit.edu> <CAMMESsxo56ZK+DKBMkKvFcXf+1GFPF+wDtRCW=+md8WCoKODxw@mail.gmail.com> <63cbb2b2-e7ec-3077-ab4d-258ce95e6ef7@cisco.com> <FCE03BA7-39DB-44A4-9E3A-93E8DC0CAB31@cisco.com> <88a5c560-cb61-78c2-3733-931ffe529b6b@cisco.com>
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To: "Acee Lindem (acee)" <acee@cisco.com>, Peter Psenak <ppsenak@cisco.com>, Benjamin Kaduk <kaduk@mit.edu>
Cc: "draft-ietf-isis-mpls-elc@ietf.org" <draft-ietf-isis-mpls-elc@ietf.org>, The IESG <iesg@ietf.org>, "lsr-chairs@ietf.org" <lsr-chairs@ietf.org>, "lsr@ietf.org" <lsr@ietf.org>
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Subject: Re: [Lsr] Benjamin Kaduk's Discuss on draft-ietf-isis-mpls-elc-12: (with DISCUSS and COMMENT)
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Just for the record, I’m ok with the latest text.

Thanks!

Alvaro.

On May 26, 2020 at 10:25:38 AM, Peter Psenak (ppsenak@cisco.com) wrote:

Hi Acee,

updated the text based on your comments.

thanks,
Peter


On 26/05/2020 16:07, Acee Lindem (acee) wrote:
> Hi Peter,
>
> This is in response to the previous Email on your suggested text.
>
> On 5/26/20, 4:26 AM, "Peter Psenak" <ppsenak@cisco.com> wrote:
>
> Hi Alvaro,
>
> please see inline (##PP)
>
> On 22/05/2020 16:59, Alvaro Retana wrote:
> > On May 21, 2020 at 3:39:03 PM, Benjamin Kaduk wrote:
> >
> >
> > Peter:
> >
> > Hi!
> >
> >
> >> With respect to Alvaro's clarification, your answer for (1) makes
sense;
> >> thanks! I think Alvaro has offered to help work out what (if any)
> >> additional text we might want to be sure that the answer to (2) is
clear in
> >> the document.
> >
> > I think that #1 is where some clarification could be useful. :-)
> >
> >
> > I'm including both ISIS and OSPF suggestions below to consolidate the
> > discussion.
> >
> >
> > ...
> >>> My interpretation of Ben's question is two-fold:
> >>>
> >>> (1) Would ISIS routers normally propagate the information to a
> >>> different level? The ELC is a new prefix attribute flag -- are prefix
> >>> attributes always propagated (unchanged) to other levels? If so, then
> >>> the requirement (MUST) is not needed. My reading of rfc7794 is that
> >>> the propagation is optional...
> >>
> >> depends on the attribute or a bit. Some are propagated some are not.
> >> That's why we are saying this one MUST be preserved.
> >
> > Right.
> >
> > For ISIS I think the current text is in line with the specification of
> > the other bits in rfc7794. No changes are needed.
> >
> > If anything, you may want to change the order of this sentence to
> > address Ben's comment:
> >
> > OLD>
> > When a router propagates a prefix between ISIS levels ([RFC5302], it
> > MUST preserve the ELC signaling for this prefix.
> >
> > NEW>
> > The ELC signaling MUST be preserved when a router propagates a prefix
> > between ISIS levels ([RFC5302]).
> >
> > [Similar for OSPF.]
>
> ##PP
> done.
>
>
> >
> >
> >
> > I think that for OSPF it is not that simple...
> >
> > For OSPFv2: rfc7684 says that the "scope of the OSPFv2 Extended Prefix
> > Opaque LSA depends on the scope of the advertised prefixes", which I
> > assume means that for intra-area prefixes the scope will be
> > area-local...so the ABR wouldn't simply propagate it; it would have to
> > originate a new LSA.
>
> ##PP
> correct. It is always a new LSA that ABR needs to generate. Here it's
> actually two LSAs.
>
> >
> > Suggestion (Add to 3.1)>
> > When an OSPFv2 Area Border Router (ABR) distributes information between
> > connected areas it SHOULD originate an OSPFv2 Extended Prefix Opaque
LSA
> > [RFC7684] including the received ELC setting. If the received
information
> > is included in an LSA with an AS-wide scope, then the new LSA is not
needed.
>
> Here's my suggestion for OSPFv2 ABR related text:
>
> "The ELC signaling MUST be preserved when an OSPF Area Border Router
> (ABR) distributes information between connected areas. To do so, ABR
> MUST originate an OSPFv2 Extended Prefix Opaque LSA [RFC7684] including
> the received ELC setting."
>
> Ok - I change "connected areas" to "areas" and "ABR MUST" to "an ABR
MUST".
>
> Here's my suggested text for OSPFv2 ASBR case:
>
> "When an OSPF Autonomous System Boundary Router (ASBR) redistributes a
> prefix from another instance of OSPF or from some other protocol, it
> SHOULD preserve the ELC signaling for the prefix if it exists. To do so,
> ASBR SHOULD originate Extended Prefix Opaque LSA [RFC7684] including the
> ELC setting of the redistributed prefix. The flooding scope of the
> Extended Prefix Opaque LSA MUST match the flooding scope of the LSA that
> ASBR originates as a result of the redistribution. The exact mechanism
> used to exchange ELC between protocol instances on the ASBR is outside
> of the scope of this document."
>
> Sure - replace "ASBR SHOULD" with "an ASBR SHOULD", "that ASBR" with
"that an ASBR", and "the ASBR is" with "an ASBR is" to be consistent.
> Also, "originate Extended" with "originate an Extended".
>
>
>
> >
> >
> > For OSPFv3: The PrefixOptions are *in* the LSA, but I couldn't find
> > anything in rfc5340 saying that the received values should be copied
> > into the Inter-Area-Prefix-LSA (nor that they should not).
> >
> > Suggestion (Add to 3.2)>
> > When an OSPFv3 Area Border Router (ABR) distributes information between
> > connected areas, the setting of the ELC Flag in the
Inter-Area-Prefix-LSA
> > MUST be the same as the received value.
>
> Here's my suggestion for OSPFv3 ABR and ASBR:
>
> "The ELC signaling MUST be preserved when an OSPFv3 Area Border Router
> (ABR) distributes information between connected areas. The setting of
> the ELC Flag in the Inter-Area-Prefix-LSA [RFC5340] or in the
> Inter-Area-Prefix TLV [RFC8362], generated by ABR, MUST be the same as
> the value the ELC Flag associated with the prefix in the source area."
>
> Same change - replace "connected areas" with "areas" and "by ABR" with
"by an ABR".
>
> "When an OSPFv3 Autonomous System Boundary Router (ASBR) redistributes a
> prefix from another instance of OSPFv3 or from some other protocol, it
> SHOULD preserve the ELC signaling for the prefix if it exists. The
> setting of the ELC Flag in the AS-External-LSA [RFC5340] or in the
> External-Prefix TLV [RFC8362], generated by ASBR, MUST be the same as
> the value the ELC Flag associated with the prefix in the source domain.
> The exact mechanism used to exchange ELC between protocol instances on
> the ASBR is outside of the scope of this document.
>
> Add "NSSA-LSA" as a case. Replace "by ASBR" with "by an ASBR" and "value
the ELC" with "value of the ELC".
>
> Thanks,
> Acee
>
> thanks,
> Peter
>
>
> >
> >
> >
> >
> >>> (2) If the propagation is not automatic, and the L1L2 router doesn't
> >>> support this specification, then what are the drawbacks/failure
> >>> scenarios? IOW, for multi-level operation is it a requirement that
> >>> the L1L2 support this specification?
> >>
> >> drawback are identical to what is mentioned in the Security
> >> Considerations section.
> >
> > I think that text is ok.
> >
> >
> > Thanks!
> >
> > Alvaro.
> >
> >
>
>
>
>