Re: [bess] Mail regarding draft-ietf-bess-rfc7432bis

Hi Ali and Menachem,
thank you for the discussion of the applicability of PW CW. I would like to
bring to your attention the work at the MPLS WG on the use of the Post-stack
First Nibble (PFN).
<https://www.ietf.org/archive/id/draft-ietf-mpls-1stnibble-02.txt> I must
apologize that the draft has lapsed. The authors are finalizing updates,
and the new version will be uploaded before IETF-119. It seems like one of
the key updates in this draft, the intention to deprecate and ultimately
obsolete cases where a non-IP payload encapsulated in MPLS without the
presence of a Post-Stack Header (e.g., PW CW) is relevant to
this discussion. I've asked for a presentation slot at the BESS WG session
in Brisbane to share the update on this work.

Regards,
Greg

On Mon, Feb 5, 2024 at 10:06 AM Ali Sajassi (sajassi) <sajassi=
40cisco.com@dmarc.ietf.org> wrote:

> Hi Menachem,
>
>
>
> The use of control word is not mandatory and it is situation dependent.
> Both RFC 7432 (and now bis) and RFC 8469 (which is basically elaboration of
> section 18 of RFC7432/bis) mention that the control word is not needed when
> there is no chance of packet re-ordering – e.g., when underlay tunnel is
> RSVP-TE. Also, when the network (inclusive of all PE and P nodes) uses
> Entropy Label, then there is no chance of re-ordering either. So, we are
> just saying that in scenarios where there is no chance of packet
> re-ordering, then control word is not needed (to avoid packet re-ordering)
> – i.e. no need to tax the packet with additional 4 bytes.
>
>
>
> So, I was suggesting the text to be clarified as follow:
>
>
>
>    - If a network (inclusive of both PE and P nodes) uses entropy labels
>    per [RFC6790] for ECMP load balancing, then the control word MAY NOT be
>    used.
>
>
>
> This means if the operators still want to use the control word with EL,
> then they still can!
>
>
>
> Cheers,
>
> Ali
>
>
>
>
>
> *From: *Menachem Dodge <mdodge@drivenets.com>
> *Date: *Monday, February 5, 2024 at 5:55 AM
> *To: *Ali Sajassi (sajassi) <sajassi@cisco.com>, Matthew Bocci (Nokia)
> <matthew.bocci=40nokia.com@dmarc.ietf.org>,
> draft-ietf-bess-rfc7432bis@ietf.org <draft-ietf-bess-rfc7432bis@ietf.org>
> *Cc: *bess-chairs@ietf.org <bess-chairs@ietf.org>, bess@ietf.org <
> bess@ietf.org>
> *Subject: *Re: Mail regarding draft-ietf-bess-rfc7432bis
>
> Hello Ali,
>
>
>
> Thank you kindly for your response.
>
>
>
> The question that Mathew and I raised, is why make the control-word
> dependent on the presence of the Entropy Label (per RFC6790)?
>
>
>
> Transit Routers may or may not perform their load balancing based on the
> Entropy Label.
>
> Some transit routers do perform deep packet inspection whether or not the
> Entropy Label is present (whether or not it is needed),
> in which case the presence of the control-word is important.
>
>
>
> Why not let the network administrator decide whether a control-word should
> be present?
>
>
>
> Mathew wrote as follows, see also that the CW can be included for
> additional reasons and the reference to RFC8649:
>
> “*The head end PE has no idea what hashing mechanism is actually used
> downstream, regardless of whether the entropy label is inserted by it. The
> entropy label is just there to provide additional flow information if the
> downstream P router is load balancing based on the label stack, but it does
> not in itself prevent the P router from scanning below the bottom of stack
> and instead load balancing on the payload after checking the MPLS first
> nibble. This also seems to be superseded by RFC8469 and all the discussion
> over the years about making CW mandatory for MPLS-based services . It is
> also worth noting that CW is not just to prevent aliasing between IP and
> Ethernet traffic, but can be used to indicate OAM or other types of
> maintenance packets**.”*
>
>
>
> So, we were suggesting that the text be removed, to remove the dependency
> between the Entropy label and the control-word.
>
>
>
> And then, we would need an errata for RFC 8214 to remove the following text:
>
>   “If a network uses entropy labels per [RFC6790 <https://datatracker.ietf.org/doc/html/rfc6790>], then the C Flag
>
>    MUST NOT be set, and the control word MUST NOT be used when sending
> EVPN-encapsulated packets over a P2P LSP.”
>
>
>
> Appreciate your inputs in understanding if there is indeed a reason for
> the dependency between the Entropy Label (per RFC6790) and the CW.
>
>
>
> Thank you kindly.
>
>
>
> Best Regards,
>
> Menachem
>
>
>
>
>
> *From: *Ali Sajassi (sajassi) <sajassi@cisco.com>
> *Date: *Monday, 5 February 2024 at 7:52
> *To: *Menachem Dodge <mdodge@drivenets.com>, Matthew Bocci (Nokia)
> <matthew.bocci=40nokia.com@dmarc.ietf.org>,
> draft-ietf-bess-rfc7432bis@ietf.org <draft-ietf-bess-rfc7432bis@ietf.org>
> *Cc: *bess-chairs@ietf.org <bess-chairs@ietf.org>, bess@ietf.org <
> bess@ietf.org>
> *Subject: *Re: Mail regarding draft-ietf-bess-rfc7432bis
>
> CAUTION: External E-Mail - Use caution with links and attachments
>
>
>
> Hi Matthew, Menachem:
>
>
>
> The text in the yellow says: “If a network uses entropy labels per
> [RFC6790]” …
>
> It should be noted that the word “network” is used which is inclusive of
> all the PE and P nodes in that network. So, if the network uses entropy
> labels and does ECMP based on that, then there shouldn’t be a need for
> control word. However, I don’t mind changing it from “SHOULD NOT” to “MAY
> NOT”.
>
>
>
> Cheers,
>
> Ali
>
>
>
> *From: *Menachem Dodge <mdodge@drivenets.com>
> *Date: *Sunday, February 4, 2024 at 12:39 AM
> *To: *Matthew Bocci (Nokia) <matthew.bocci=40nokia.com@dmarc.ietf.org>,
> draft-ietf-bess-rfc7432bis@ietf.org <draft-ietf-bess-rfc7432bis@ietf.org>
> *Cc: *bess-chairs@ietf.org <bess-chairs@ietf.org>, bess@ietf.org <
> bess@ietf.org>
> *Subject: *Re: Mail regarding draft-ietf-bess-rfc7432bis
>
> Hello Mathew,
>
>
>
> Just wondering if you received a response to your email, as I have not
> seen any responses to either of our emails on the list.
>
>
>
> Thank you kindly.
>
>
>
> Best Regards,
>
> Menachem
>
>
>
> *From: *BESS <bess-bounces@ietf.org> on behalf of Matthew Bocci (Nokia)
> <matthew.bocci=40nokia.com@dmarc.ietf.org>
> *Date: *Tuesday, 30 January 2024 at 17:42
> *To: *draft-ietf-bess-rfc7432bis@ietf.org <
> draft-ietf-bess-rfc7432bis@ietf.org>
> *Cc: *bess-chairs@ietf.org <bess-chairs@ietf.org>, bess@ietf.org <
> bess@ietf.org>
> *Subject: *Re: [bess] Mail regarding draft-ietf-bess-rfc7432bis
>
> CAUTION: External E-Mail - Use caution with links and attachments
>
>
>
> Hi Authors
>
>
>
> Resending this and including the WG. I believe this is a similar question
> to the one posted by Menachem on RFC8214.
>
>
>
> Thanks in advance
>
>
>
> Matthew
>
>
>
> *From: *Matthew Bocci (Nokia) <matthew.bocci@nokia.com>
> *Date: *Monday, 15 January 2024 at 12:40
> *To: *draft-ietf-bess-rfc7432bis@ietf.org <
> draft-ietf-bess-rfc7432bis@ietf.org>
> *Cc: *bess-chairs@ietf.org <bess-chairs@ietf.org>
> *Subject: *Mail regarding draft-ietf-bess-rfc7432bis
>
> Hi Authors
>
>
>
> There is there following restriction (highlighted in yellow) on the use of
> the control word in EVPN where the EL/ELI is used. I know this was
> inherited from RFC7432, but do you know why this is the case (in particular
> a SHOULD NOT)?
>
>
>
> The head end PE has no idea what hashing mechanism is actually used
> downstream, regardless of whether the entropy label is inserted by it. The
> entropy label is just there to provide additional flow information if the
> downstream P router is load balancing based on the label stack, but it does
> not in itself prevent the P router from scanning below the bottom of stack
> and instead load balancing on the payload after checking the MPLS first
> nibble. This also seems to be superseded by RFC8469 and all the discussion
> over the years about making CW mandatory for MPLS-based services . It is
> also worth noting that CW is not just to prevent aliasing between IP and
> Ethernet traffic, but can be used to indicate OAM or other types of
> maintenance packets.
>
>
>
> Can we just remove the text in yellow?
>
>
>
> Thanks
>
>
>
> Matthew
>
>
>
>
>
> In order to avoid frame misordering described above, the following
>
>    network-wide rules are applied:
>
>
>
>    *  If a network uses deep packet inspection for its ECMP, then the
>
>       the following rules for "Preferred PW MPLS Control Word" [RFC4385]
>
>       apply:
>
>
>
>       -  It MUST be used with the value 0 (e.g., a 4-octet field with a
>
>          value of zero) when sending unicast EVPN-encapsulated packets
>
>          over an MP2P LSP.
>
>
>
>       -  It SHOULD NOT be used when sending EVPN-encapsulated packets
>
>          over a P2MP or P2P RSVP-TE LSP.
>
>
>
>       -  It SHOULD be used with the value 0 when sending EVPN-
>
>          encapsulated packets over a mLDP P2MP LSP.  There can be
>
>          scenarios where multiple links or tunnels can exist between two
>
>          nodes and thus it is important to ensure that all packets for a
>
>          given flows take the same link (or tunnel) between the two
>
>          nodes.
>
>
>
>    *  If a network uses entropy labels per [RFC6790], then the control
>
>       word SHOULD NOT be used.
>
>
>
>
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