Re: [Bier] What is the motivation for RFC8401 to have a strict "MUST NOT be set" for R-Flag?

"Les Ginsberg (ginsberg)" <ginsberg@cisco.com> Tue, 07 August 2018 15:56 UTC

From: "Les Ginsberg (ginsberg)" <ginsberg@cisco.com>
To: "Van De Velde, Gunter (Nokia - BE/Antwerp)" <gunter.van_de_velde@nokia.com>, "bier@ietf.org" <bier@ietf.org>, Tony Przygienda <tonysietf@gmail.com>, "lsr@ietf.org" <lsr@ietf.org>
CC: "Bidgoli, Hooman (Nokia - CA/Ottawa)" <hooman.bidgoli@nokia.com>
Thread-Topic: What is the motivation for RFC8401 to have a strict "MUST NOT be set" for R-Flag?
Thread-Index: AdQuOt85jH56m2TUR+uXXuoqthRMlgAK6gDw
Date: Tue, 07 Aug 2018 15:56:47 +0000
Message-ID: <8604646bebc4452e9072c91f7db5cfbd@XCH-ALN-001.cisco.com>
References: <AM5PR0701MB1729E94EB59F656676E85833E0270@AM5PR0701MB1729.eurprd07.prod.outlook.com>
In-Reply-To: <AM5PR0701MB1729E94EB59F656676E85833E0270@AM5PR0701MB1729.eurprd07.prod.outlook.com>
Accept-Language: en-US
Content-Language: en-US
Content-Type: multipart/alternative; boundary="_000_8604646bebc4452e9072c91f7db5cfbdXCHALN001ciscocom_"
MIME-Version: 1.0
Archived-At: <https://mailarchive.ietf.org/arch/msg/bier/WQIBPbo3LqqKVEVZ4wL6M5bMfAc>
Subject: Re: [Bier] What is the motivation for RFC8401 to have a strict "MUST NOT be set" for R-Flag?
Precedence: list

Gunter -

In early versions of the draft we did not support inter-area, so we specified that R bit MUST be 0.
Then in V6 of the draft we allowed for inter-area support and the text relating to R-bit was removed.

However, somehow the text regarding R-bit ended up being put back in V9 of the draft. I don't think there was any reason for this - probably just a cut and paste error.

At this point I think you will need to file an Errata.

Sigh...

    Les


From: Van De Velde, Gunter (Nokia - BE/Antwerp) <gunter.van_de_velde@nokia.com>
Sent: Tuesday, August 07, 2018 3:40 AM
To: bier@ietf.org; Les Ginsberg (ginsberg) <ginsberg@cisco.com>; Tony Przygienda <tonysietf@gmail.com>; lsr@ietf.org
Cc: Bidgoli, Hooman (Nokia - CA/Ottawa) <hooman.bidgoli@nokia.com>
Subject: What is the motivation for RFC8401 to have a strict "MUST NOT be set" for R-Flag?

Folks,

When having desire to do BIER between ISIS L1/L2 domains then there is something I do not understand.

In RFC8401 I see:
4.2<https://tools.ietf.org/html/rfc8401#section-4.2>.  Advertising BIER Information

   BIER information advertisements are associated with a new sub-TLV in

   the extended reachability TLVs.  BIER information is always

   associated with a host prefix, which MUST be a node address for the

   advertising node.  If this is not the case, the advertisement MUST be

   ignored.  Therefore, the following restrictions apply:



   o  Prefix length MUST be 32 for an IPv4 prefix or 128 for an IPv6

      prefix.



   o  When the Prefix Attributes Flags sub-TLV [RFC7794<https://tools.ietf.org/html/rfc7794>] is present, the

      N flag MUST be set and the R flag MUST NOT be set.



   o  BIER sub-TLVs MUST be included when a prefix reachability

      advertisement is leaked between levels.

In RFC7794 I find:


   R-Flag:  Re-advertisement Flag (Bit 1)

      Set when the prefix has been leaked from one level to another

      (upwards or downwards).

The issue that is unclear to me:


  *   If I leak a (node-)prefix between L1/L2 then I MUST set the R-flag (according RFC7794), but then this seem to contradict the strict MUST NOT from RFC8401.

What logic am I misunderstanding? Why is the motivation in RFC8401 regarding the strict "MUST NOT be set" requirement for the R-Flag?

Brgds,
G/

[Bier] What is the motivation for RFC8401 to have… Van De Velde, Gunter (Nokia - BE/Antwerp)
Re: [Bier] What is the motivation for RFC8401 to … Les Ginsberg (ginsberg)
Re: [Bier] What is the motivation for RFC8401 to … Van De Velde, Gunter (Nokia - BE/Antwerp)