Re: Size of CR in CRH

"Joel M. Halpern" <jmh@joelhalpern.com> Wed, 20 May 2020 00:49 UTC

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Subject: Re: Size of CR in CRH
To: Nick Hilliard <nick@foobar.org>, Ron Bonica <rbonica@juniper.net>
Cc: 6man <6man@ietf.org>, Bob Hinden <bob.hinden@gmail.com>
References: <DM6PR05MB6348E9AD1E088792C2F10BB4AEBF0@DM6PR05MB6348.namprd05.prod.outlook.com> <8CC3F837-B4D6-4570-AF2F-37041839F391@employees.org> <21E9A957-1A31-4A11-8E78-5F7E382866D4@juniper.net> <CAOj+MMEONA5OtWz9Y7pTt4WyVsb+7-_wEKPVryyHLncHG6ew6g@mail.gmail.com> <CALx6S35fPrnh6UtpPYmQ6Yew6D2QVMvYTdp0AaGr8jYhGNKk3A@mail.gmail.com> <CAOj+MMH0Q6ASmjPdmgNB2LHDhvCL2u2DLB9SBRLnJnCD3EbA4w@mail.gmail.com> <CAO42Z2wke4Lw44zdE0G9CJq3rXh69jsxjO5=RTcCv9EXdNOp5A@mail.gmail.com> <BC6A6354-BAB5-4CE0-ABEB-73B4C88E149A@gmail.com> <a8220864-302a-3698-c61d-abb7926482fa@foobar.org> <DM6PR05MB6348945F596A016E6F11856EAEB90@DM6PR05MB6348.namprd05.prod.outlook.com> <6c86cc62-81fd-1204-13db-9ba535f36f67@foobar.org>
From: "Joel M. Halpern" <jmh@joelhalpern.com>
Message-ID: <022fe532-4763-608b-6688-efe7f4adf101@joelhalpern.com>
Date: Tue, 19 May 2020 20:49:22 -0400
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Ugg.  I had simply assumed that domains would use one or the other size. 
  You are correct Nick, as written so far, a domain could use both 
sizes, as long as any given packet used one or the other.
I would recommend that we write explicitly that a domain SHOULD use only 
one size, and the confusions if one chooses otherwise are on the 
operator who has done that to themselves.

I have been told that there are operators who want 16 bit CRH SIDs and 
operators who want 32 bit CRH SIDs.  That seems to be more significant 
than the minor simplification of defining only one.  I won't cry if the 
working group picks just one.

Yours,
Joel

On 5/19/2020 7:35 PM, Nick Hilliard wrote:
> Ron Bonica wrote on 19/05/2020 19:01:
>> So, allocating two Routing types may be the best solution.
> 
> yeah, the hardware constraints requirement is troublesome - hey, we're 
> all ToR junkies these days - but the more I think about it, the more 
> complex this becomes from an operational / implementation point of view, 
> for example:
> 
> - do you define SID size on a per domain or per node or a per-SID + 
> per-node basis?
> 
> - if per-domain, how do you implement non-service affecting migration 
> from 16-bit to 32-bit?
> 
> - without using differentiating CLI syntax, can you manually define a 
> mechanism to allow a 16-bit identifier to be configured in a 32-bit SID?
> 
> - the distribution protocols needs to become aware of multiple SID sizes
> 
> - is (sid16)32768 the same as (sid32)32768. If not, why not? If so, then 
> why?  How can this be explained either by or to the TAC agent at 03:00 
> over a noisy, laggy phone line in a time-constrained maintenance window 
> involving a P1 where neither of you speaks the other's language natively?
> 
> - how many segments do you really need to program for actual networks 
> (1? 10? 50?), and how deep can you inspect on merchant silicon of today, 
> and currently in development? I.e. how badly would your flexibility be 
> hobbled if SIDs were one size only?
> 
> Nick
> 
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