Re: [bess] Encoding a 20 bit label in a 24 bit field.

Greg Mirsky <gregimirsky@gmail.com> Mon, 22 October 2018 22:07 UTC

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From: Greg Mirsky <gregimirsky@gmail.com>
Date: Mon, 22 Oct 2018 15:07:39 -0700
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To: Stephane Litkowski <stephane.litkowski@orange.com>
Cc: "Ali Sajassi (sajassi)" <sajassi@cisco.com>, "Jakob Heitz (jheitz)" <jheitz@cisco.com>, zhuangshunwan@huawei.com, BESS <bess@ietf.org>
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Subject: Re: [bess] Encoding a 20 bit label in a 24 bit field.
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Hi Stephane,
should note that "setting the MPLS Label field to zero" may be also
interpreted as a valid label, IPv4 Explicit Null Label.

Regards,
Greg

On Mon, Oct 22, 2018 at 6:47 AM <stephane.litkowski@orange.com> wrote:

> Hi,
>
> Does anyone disagree with the additional Jakob's statement proposal ?
> " The lower order 4 bits SHOULD be sent as 0 and ignored on receipt."
>
> As an example, in MVPN for PMSI tunnel attribute, we have the following
> statement which does not tell anything about the lower order bits:
> " If the MPLS Label field is non-zero, then it contains an MPLS label
>    encoded as 3 octets, where the high-order 20 bits contain the label
>    value.  Absence of an MPLS Label is indicated by setting the MPLS
>    Label field to zero."
>
>
> Brgds,
>
>
> -----Original Message-----
> From: BESS [mailto:bess-bounces@ietf.org] On Behalf Of Ali Sajassi
> (sajassi)
> Sent: Tuesday, October 16, 2018 19:30
> To: Jakob Heitz (jheitz); Zhuangshunwan; BESS
> Subject: Re: [bess] Encoding a 20 bit label in a 24 bit field.
>
>
> Yes, just the encoding of label value needs to be clear.
>
> Cheers,
> Ali
>
>
>
> On 10/15/18, 6:24 PM, "BESS on behalf of Jakob Heitz (jheitz)" <
> bess-bounces@ietf.org on behalf of jheitz@cisco.com> wrote:
>
>     How about:
>     The lower order 4 bits SHOULD be sent as 0 and ignored on receipt.
>
>     Regards,
>     Jakob.
>
>
>     -----Original Message-----
>     From: Zhuangshunwan <zhuangshunwan@huawei.com>
>     Sent: Monday, October 15, 2018 6:02 PM
>     To: Jakob Heitz (jheitz) <jheitz@cisco.com>om>; BESS <bess@ietf.org>
>     Subject: RE: Encoding a 20 bit label in a 24 bit field.
>
>     It is good to make this explicit. This ambiguity has led to some
> unnecessary interworking problems.
>
>     Should we also need to explicitly define the "bottom of stack" bit in
> the low-order bit of the 3-octet label field?
>
>     Thanks,
>     Shunwan
>
>     -----Original Message-----
>     From: BESS [mailto:bess-bounces@ietf.org] On Behalf Of Jakob Heitz
> (jheitz)
>     Sent: Tuesday, October 16, 2018 4:21 AM
>     To: BESS <bess@ietf.org>
>     Subject: [bess] Encoding a 20 bit label in a 24 bit field.
>
>     We have proposed the following erratum for RFC 7432.
>
>     Opinions?
>
>     Regards,
>     Jakob.
>
>
>     -----Original Message-----
>     From: RFC Errata System <rfc-editor@rfc-editor.org>
>     Sent: Friday, October 12, 2018 12:37 PM
>     To: Ali Sajassi (sajassi) <sajassi@cisco.com>om>; raggarwa_1@yahoo.com;
> nabil.n.bitar@verizon.com; aisaac71@bloomberg.net; uttaro@att.com;
> jdrake@juniper.net; wim.henderickx@alcatel-lucent.com; db3546@att.com;
> aretana.ietf@gmail.com; martin.vigoureux@nokia.com; Giles Heron (giheron)
> <giheron@cisco.com>om>; nabil.n.bitar@verizon.com
>     Cc: Krishnamoorthy Arumugham (karumugh) <karumugh@cisco.com>om>;
> l2vpn@ietf.org; rfc-editor@rfc-editor.org
>     Subject: [Technical Errata Reported] RFC7432 (5523)
>
>     The following errata report has been submitted for RFC7432, "BGP
> MPLS-Based Ethernet VPN".
>
>     --------------------------------------
>     You may review the report below and at:
>     http://www.rfc-editor.org/errata/eid5523
>
>     --------------------------------------
>     Type: Technical
>     Reported by: Krishnamoorthy Arumugham <karumugh@cisco.com>
>
>     Section: 7
>
>     Original Text
>     -------------
>     Clarifications to following sub-sections:
>     Section 7.1
>     Section 7.2
>     Section 7.5
>
>
>     Corrected Text
>     --------------
>     Section 7.1:
>     Add below text to the section 7.1 regarding the encoding of MPLS label:
>
>     "The value of the 20-bit MPLS label is encoded in the high-order 20
> bits of the 3 bytes MPLS Label field."
>
>     Section 7.2:
>     Add below text to the section 7.2 regarding the encoding of both the
> MPLS label fields:
>
>     "The value of the 20-bit MPLS label is encoded in the high-order 20
> bits of the 3 bytes MPLS Label field for both MPLS Label1 and MPLS Label2."
>
>     Section 7.5:
>     Add below text to the section 7.5 regarding the encoding of ESI Label
> fields:
>
>     "The value of the 20-bit MPLS label is encoded in the high-order 20
> bits of the ESI Label field."
>
>
>     Notes
>     -----
>     MPLS label is a 20-bit value and is stored in a 3 bytes field in a
> packet. The 20-bit MPLS label value is generally stored in higher order 20
> bits of the 3 byte label field. The exact encoding to be followed for
> storing MPLS label values are not explicitly mentioned in the RFC 7432
> under section 7.1, 7.2 and 7.5 for different types of EVPN routes. This
> lead to ambiguity in different implementations. Hence a clarification is
> required.
>
>     Instructions:
>     -------------
>     This erratum is currently posted as "Reported". If necessary, please
>     use "Reply All" to discuss whether it should be verified or
>     rejected. When a decision is reached, the verifying party
>     can log in to change the status and edit the report, if necessary.
>
>     --------------------------------------
>     RFC7432 (draft-ietf-l2vpn-evpn-11)
>     --------------------------------------
>     Title               : BGP MPLS-Based Ethernet VPN
>     Publication Date    : February 2015
>     Author(s)           : A. Sajassi, Ed., R. Aggarwal, N. Bitar, A.
> Isaac, J. Uttaro, J. Drake, W. Henderickx
>     Category            : PROPOSED STANDARD
>     Source              : Layer 2 Virtual Private Networks
>     Area                : Routing
>     Stream              : IETF
>     Verifying Party     : IESG
>
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