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Re: SRH TLV Type change

Tom Herbert <tom@herbertland.com> Wed, 05 June 2019 21:42 UTC

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From: Tom Herbert <tom@herbertland.com>
Date: Wed, 05 Jun 2019 14:42:20 -0700
Message-ID: <CALx6S36oFitCRW=roEwaDQUdipG8KA9B1U5SKYBMtAUWPLSxeQ@mail.gmail.com>
Subject: Re: SRH TLV Type change
To: "Darren Dukes (ddukes)" <ddukes@cisco.com>
Cc: IPv6 List <ipv6@ietf.org>
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On Wed, Jun 5, 2019 at 2:20 PM Darren Dukes (ddukes) <ddukes@cisco.com> wrote:
>
> Tom, I believe we had this conversation long ago.
> The number space is disjoint for option and SRH TLVs so the numeric values for PAD TLV types for option vs SRH TLVs is not relevant.

PAD1 and PADN are different. Even if the namespace for all types are
different, we can still leverage common values here.

>
> On the other hand there are macros used by implementations that have had fixed values for 2 years.
>
And exactly what implementations are those?

> Either way an implementation’s equivalent of the Linux ip6_parse_tlv needs to be duplicated for SRH TLVs or simply modified to support the two number spaces.

Yes, but if you look closely you'll there are only two values and the
default case in the switch statement. Those two explictly cases are
exactly PAD1 and PADN. Other cases are handled by table lookup which
is easy enough to abstract out to allow different number spaces. I
have the implementation that does this and will post shortly.

Tom

>
> Darren
>
> > On Jun 5, 2019, at 2:46 PM, Tom Herbert <tom@herbertland.com> wrote:
> >
> > On Wed, Jun 5, 2019 at 11:06 AM Darren Dukes (ddukes) <ddukes@cisco.com> wrote:
> >>
> >> In revision 18/19, PAD0 and PADN were moved to TLV Type 0 and 1 (section 8.2)
> >> I was reminded that type 1 conflicted with previous versions of the draft and implementations.
> >> In revision 20 I plan to move the PADN type back to 4 (its value from previous revisions/implementations) and add text to highlight the reservations for previous versions and implementations.
> >
> > Darren,
> >
> > Please don't do this. If PAD1 is type 0 and PADN is type 1 then that
> > is consistent with HBH and DO. This way we can use a common
> > implementation of the parsing loop (type and length byte definitions
> > are also common). Besides, in the SRH draft only one implementation
> > (Linux) is reported to have implemented TLVs and that implementation
> > does not support padding yet.
> >
> > Tom
> >
> >>
> >> Darren
> >> --------------------------------------------------------------------
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>

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