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

Robert Raszuk <robert@raszuk.net> Fri, 29 November 2019 14:01 UTC

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From: Robert Raszuk <robert@raszuk.net>
Date: Fri, 29 Nov 2019 15:01:30 +0100
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To: Gunter Van De Velde <guntervandeveldecc@icloud.com>
Cc: "Van De Velde, Gunter (Nokia - BE/Antwerp)" <gunter.van_de_velde@nokia.com>, "idr@ietf.org" <idr@ietf.org>, Sue Hares <shares@ndzh.com>
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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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Gunter,

What is there to validate ? You validate if the flow spec update is
legitimate and at most comparing destination match against unicast src
which in all of redirect use cases will be disabled anyway - you can not
possibly consider valid rule to redirect coming from your eBGP peer :).

Also pls observe that you never validate actual actions ... what I am
suggesting is just a little add-on in actions.

Thx,
R.

On Fri, Nov 29, 2019 at 11:13 AM Gunter Van De Velde <
guntervandeveldecc@icloud.com>; wrote:

> Hi Robert,
>
> While understanding your point, it does feel like opening a potential can
> of worms with respect to validation of all possible combinations humanly
> possible. Is the use-case for this capability solid enough that we need
> this complication? There seems nothing broken with keeping things simple.
>
> G/
>
> Sent from iCloud
>
> On November 29, 2019 at 10:34 AM, Robert Raszuk <robert@raszuk.net>; wrote:
>
> Gunter,
>
> To your and Jeff's point regarding multiple redirect rules I have a bit
> different perspective.
>
> First let's observe that redirect could be realized in two forms (both are
> valid and used in practice):
>
> -A- redirect of the original flow
> -B- redirect of copy of the flow
>
> See while in -A- clearly one redirect must be used, in -B- on the
> other hand multiple redirects should be supported. One span, one security
> TAP, one TCP analyzer etc ...
>
> Your draft defines -A-. To add -B- all what is needed is just one bit
> flag.
>
> Would you consider it ?
>
> Cheers,
> R.
>
>
>
>
>
> On Fri, Nov 29, 2019 at 4:51 AM Van De Velde, Gunter (Nokia - BE/Antwerp) <
> gunter.van_de_velde@nokia.com>; wrote:
>
>> 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>; 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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