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

["Ali Sajassi (sajassi)" <[e-mail]>]

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 <[e-mail]>
Date: Monday, February 5, 2024 at 5:55 AM
To: Ali Sajassi (sajassi) <[e-mail]>, Matthew Bocci (Nokia) <matthew.bocci=[e-mail]>, [e-mail] <[e-mail]>
Cc: [e-mail] <[e-mail]>, [e-mail] <[e-mail]>
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 This also seems to be superseded by RFC8469 and all the discussion over the years about making CW mandatory for MPLS-based services .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) <[e-mail]>
Date: Monday, 5 February 2024 at 7:52
To: Menachem Dodge <[e-mail]>, Matthew Bocci (Nokia) <matthew.bocci=[e-mail]>, [e-mail] <[e-mail]>
Cc: [e-mail] <[e-mail]>, [e-mail] <[e-mail]>
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 <[e-mail]>
Date: Sunday, February 4, 2024 at 12:39 AM
To: Matthew Bocci (Nokia) <matthew.bocci=[e-mail]>, [e-mail] <[e-mail]>
Cc: [e-mail] <[e-mail]>, [e-mail] <[e-mail]>
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 <[e-mail]> on behalf of Matthew Bocci (Nokia) <matthew.bocci=[e-mail]>
Date: Tuesday, 30 January 2024 at 17:42
To: [e-mail] <[e-mail]>
Cc: [e-mail] <[e-mail]>, [e-mail] <[e-mail]>
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) <[e-mail]>
Date: Monday, 15 January 2024 at 12:40
To: [e-mail] <[e-mail]>
Cc: [e-mail] <[e-mail]>
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.