Re: [Idr] WG LC draft-ietf-idr-flowspec-path-redirect-10.txt [11/17/2019 to 12/2/2019]

"Van De Velde, Gunter (Nokia - BE/Antwerp)" <gunter.van_de_velde@nokia.com> Fri, 29 November 2019 03:51 UTC

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From: "Van De Velde, Gunter (Nokia - BE/Antwerp)" <gunter.van_de_velde@nokia.com>
To: Jeffrey Haas <jhaas@pfrc.org>, Sue Hares <shares@ndzh.com>
CC: "idr@ietf.org" <idr@ietf.org>
Thread-Topic: [Idr] WG LC draft-ietf-idr-flowspec-path-redirect-10.txt [11/17/2019 to 12/2/2019]
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Date: Fri, 29 Nov 2019 03:51:35 +0000
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Subject: Re: [Idr] WG LC draft-ietf-idr-flowspec-path-redirect-10.txt [11/17/2019 to 12/2/2019]
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Hi Jeff,

Thanks for the feedback and suggestions.

See inline: GV>

-----Original Message-----
From: Idr <idr-bounces@ietf.org>; On Behalf Of Jeffrey Haas
Sent: Thursday, November 28, 2019 20:21
To: Sue Hares <shares@ndzh.com>;
Cc: idr@ietf.org
Subject: Re: [Idr] WG LC draft-ietf-idr-flowspec-path-redirect-10.txt [11/17/2019 to 12/2/2019]

Sue,



> On Nov 18, 2019, at 12:41 AM, Susan Hares <shares@ndzh.com<mailto:shares@ndzh.com>> wrote:
>
> This begins a 2 week WG Last call on draft-idr-flowspec-path-redirect-10.txt from [11/17/2019 to 12/2/2019].
>
> You can obtain the draft at:
>
> https://datatracker.ietf.org/doc/draft-ietf-idr-flowspec-path-redirect/
>
> Consider in your review whether this draft:
>
> 1)      Is compatible with draft-ietf-rfc5575bis-17.txt?

Yes.  (Close enough.)  The current version of the draft is implementable.

> 2)      Whether the draft is useful for deployments of flow specification

It can be useful.

> 3)      Is this technology ready for deployment?
> 4)      Is the write-up of this technology in draft-ietf-idr-flowspec-path-redirect clearly written and ready for publication?

Ready with minor issues, IMO:

Procedure-wise, there needs to be a bit more text covering cases about interactions with other traffic actions.  This was a known headache for similar drafts such as redirect-to-ip.  In particular, interaction with redirect-to-ip and redirect-to-vrf is needed.

GV> Section "6. Validation Procedures" gives input on this. We discussed this with you long ago and hence this text was added.

"
   While it MUST NOT happen, and is seen as invalid combination, it is
   possible from a semantics perspective to have multiple clashing
   redirect actions defined within a single flowspec rule.  For best and
   consistant compatibility with legacy implementations, the redirect
   functionality as documented by rfc5575bis MUST NOT be broken, and
   hence when a clash occurs, then rfc5575bis based redirect MUST take
   priority.
"

This means that redirect-to-VRF will take absolute priority to not break rfc5575bis behavior.
Having also redirect-to-ip will result in an invalid


The text "A single flowspec rule MUST NOT have more as one indirection-id per S-ID.  On a flowspec client the indirection-id with lowest S-ID MUST be imposed first for any given flowspec entry."  There's no procedure for what happens in error handling when you do have more than one of the same S-ID.  The text about the case for S-ID of 0 is also a bit ambiguous.  It feels like it's reading "there is no sequence", but what do you do when you then have ones that do?

GV> What about the following rewrite:

Original:
    The 'S-ID' field identifies a 4 bit Sequence ID field.  This field is
   used to provide a flowspec client an indication how and where to
   sequence the received indirection-ids.  The Sequence ID value 0
   indicates that Sequence ID field is NOT set and SHOULD be ignored.  A
   single flowspec rule MUST NOT have more as one indirection-id per
   S-ID.  On a flowspec client the indirection-id with lowest S-ID MUST
   be imposed first for any given flowspec entry.

New:
   The 'S-ID' field identifies a 4 bit Sequence ID field.  This field is
   used to provide a flowspec client an indication how and where to
   sequence the received indirection-ids.  The Sequence ID value 0
   indicates that Sequence ID field is NOT set and **all other sequence ID's**
   SHOULD be ignored.  A
   single flowspec rule MUST NOT have more as one indirection-id per
   S-ID.  On a flowspec client the indirection-id with lowest S-ID MUST
   be imposed first for any given flowspec entry.

GV> In section *6. Validation procedure" there is text to handle the error condition when the flowspec rule results in an invalid redirection, that prescribe what needs to happen when the "redirect to indirection-id" does not result in a valid redirection:

"
   While it MUST NOT happen, and is seen as invalid combination, it is
   possible from a semantics perspective to have multiple clashing
   redirect actions defined within a single flowspec rule.  For best and
   consistant compatibility with legacy implementations, the redirect
   functionality as documented by rfc5575bis MUST NOT be broken, and
   hence when a clash occurs, then rfc5575bis based redirect MUST take
   priority.  Additionally, if the "Redirect to indirection-id" does not
   result in a valid redirection, then the flowspec rule MUST be
   processed as if the "Redirect to indirection-id" community was not
   attached to the flowspec route.
"

GV> Is there more to add to this? (We could add a line to detail that "redirect-to-ip" is incompatible with "redirect to indirection-id" and result in invalid redirection rule, however to me that is already implied with enough detail in the text above)

A few IANA issues:
I see the type registry is currently registered with IANA (code point 0x09).  However, the sub-type registry is not established for some reason?
The ID-Type field likely needs its own IANA registry.  Values 1-5 are defined in this draft.

GV> Correct. There is a reason for this. When we asked IANA the code-points they informed me that once the document get to RFC the sub-type registry will be established by IANA.

The flags field (one octet) currently has 3 bits reserved.  In the past, we've not done a registry for such cases (c.f. graceful restart) until we need to start carving out those reserved bits for future extensions.  I leave it to the chairs' opinion whether we want this a priori or not.

G/


>
> Thank you for considering this draft.
>
> Cheerily, Susan Hares
>
> _______________________________________________
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> Idr@ietf.org<mailto:Idr@ietf.org>
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