Re: [Lsr] Éric Vyncke's Discuss on draft-ietf-ospf-ospfv2-hbit-11: (with DISCUSS and COMMENT)

Padma Pillay-Esnault <padma.ietf@gmail.com> Mon, 02 December 2019 20:44 UTC

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From: Padma Pillay-Esnault <padma.ietf@gmail.com>
Date: Mon, 2 Dec 2019 12:44:20 -0800
Message-ID: <CAG-CQxqeJe1COhZN88y5_870=hnh_BNHcOr83ta2JuTkeObBqA@mail.gmail.com>
To: "Eric Vyncke (evyncke)" <evyncke@cisco.com>
Cc: Alvaro Retana <aretana.ietf@gmail.com>, =?UTF-8?Q?=C3=89ric_Vyncke_via_Datatracker?= <noreply@ietf.org>, The IESG <iesg@ietf.org>, "lsr-chairs@ietf.org" <lsr-chairs@ietf.org>, Yingzhen Qu <yingzhen.ietf@gmail.com>, "draft-ietf-ospf-ospfv2-hbit@ietf.org" <draft-ietf-ospf-ospfv2-hbit@ietf.org>, "lsr@ietf.org" <lsr@ietf.org>
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Hello Eric

On Mon, Dec 2, 2019 at 12:31 PM Eric Vyncke (evyncke) <evyncke@cisco.com>
wrote:

> Alvaro
>
> I do not mind too much the transient inconsistencies but more about longer
> term inconsistencies (1) hence my question about simulations / tests in the
> absence of mathematical proof.
>
The R-bit has always been in OSPFv3 (AFAIK), so, OSPFv3 does not have the
> same issue.
>
> -éric
>
> (1) having some routers being H-bit aware and other routers not processing
> the H-bit could probably introduce long term inconsistencies and loops.
>
>
As described in section 5
"All routers supporting H-Bit MUST check all the RI LSAs of nodes in the
area before actively running the modified SPF to account for the H-bit in
order to verify that all routers are in routing capability. If any router
does not advertise the Host Router Support capability then the SPF
Modifications (Section 4) MUST NOT be used in the area."

The H-bit aware routers will revert to normal operation if they detect
routers not processing the H-bit. Therefore, if ever there is a discrepancy
it not cause long term inconsistencies nor loops. In effect, H-bit
processing is either done by all or no one in the area.

Let me know if this answers your question.
Padma



> On 02/12/2019, 17:59, "iesg on behalf of Alvaro Retana" <
> iesg-bounces@ietf.org on behalf of aretana.ietf@gmail.com> wrote:
>
>     On November 30, 2019 at 11:21:01 AM, Éric Vyncke wrote:
>
>     Eric:
>
>     Hi!
>
>     > == DISCUSS ==
>     >
>     > -- Section 5 --
>     > The risk of having inconsistent view of the topology with H-bit
> aware and
>     > unaware routers seems possible to me (albeit perhaps only
> transient). Has
>     > this feature been tested / simulated in large scale networks?
>
>     Yes, as with other operations in a network (reconvergence, for
>     example), there is a risk of transient inconsistency.  §5 already
>     makes recommendations to mitigate transient states.  What explicitly
>     are you looking for to address your DISCUSS?
>
>     I'll let the authors reply about tests/simulations.
>
>     Thanks!
>
>     Alvaro.
>
>
>
>