Re: [Lsr] When is an IANA Registry Required

Robert –

My experience with Wireshark does not match yours.

In my experience, packet decoders aren’t always up on the latest spec revisions – it is always a catchup game – but it isn’t true that only values from an IANA registry are displayed.
And from an implementation standpoint, the engineer writing the decoder always has to look at the draft/RFC. An IANA Registry does not provide the format of the fixed fields (e.g., prefix, metric) – so I have a hard time agreeing with your perception that implementors only look at IANA registries.
I actually think it is the other way round – they look at drafts/RFCs and only look at registries when the document points to them. 😊

    Les

From: Robert Raszuk <robert@raszuk.net>
Sent: Tuesday, March 16, 2021 4:46 PM
To: Les Ginsberg (ginsberg) <ginsberg@cisco.com>
Cc: Alvaro Retana <aretana.ietf@gmail.com>; lsr@ietf.org; Christian Hopps <chopps@chopps.org>
Subject: Re: [Lsr] When is an IANA Registry Required

Hi Les,

I would like to share my personal experience that when debugging network issues say using wireshark or tcpdump often dissectors only decode what is in IANA registry. Anything beyond they print as hex.

Sure if someone needs to decode it he or she will find an RFC where all fields are described. But this usually requires manual labor we as lazy humans are not always best at.

So just from pure convenience (while I do understand heavy labor to move all flags to IANA) there is some operational value I could see doing it.

Best,
Robert.

On Tue, Mar 16, 2021 at 11:24 PM Les Ginsberg (ginsberg) <ginsberg=40cisco.com@dmarc.ietf.org<mailto:40cisco.com@dmarc.ietf.org>> wrote:

Alvaro -

Thanx - as always - for the thoughtful response.

I would like to state up front that I would never consider you to be a "casual reader". 😊

I am also glad you are opening this topic up to comments from others - that was my intent as well.

But one thing I find missing in your response is some info on what problem YOU think needs to be addressed?

Do you think there have already been cases where assignment of the bits in the flags field associated w a prefix or a neighbor or other object comparable to the new TLVs defined in draft-ietf-lsr-isis-srv6-extensions (e.g., Locator) has become confusing due to the lack of a registry?

I'd like to think you are motivated by more than a theoretical concern but have at least one example based on your many years of experience working on protocols.

Such an example would help me understand your motivation better and might even convince me that this is a good idea.

Thanx.

   Les

> -----Original Message-----

> From: Alvaro Retana <aretana.ietf@gmail.com<mailto:aretana.ietf@gmail.com>>

> Sent: Tuesday, March 16, 2021 12:39 PM

> To: Les Ginsberg (ginsberg) <ginsberg@cisco.com<mailto:ginsberg@cisco.com>>; draft-ietf-lsr-isis-srv6-

> extensions@ietf.org<mailto:extensions@ietf.org>

> Cc: John Scudder <jgs@juniper.net<mailto:jgs@juniper.net>>; lsr-chairs@ietf.org<mailto:lsr-chairs@ietf.org>; lsr@ietf.org<mailto:lsr@ietf.org>;

> Christian Hopps <chopps@chopps.org<mailto:chopps@chopps.org>>

> Subject: Re: When is an IANA Registry Required

>

> On February 27, 2021 at 12:57:12 PM, Les Ginsberg wrote:

>

>

> Les:

>

> Hi!

>

> Sorry for the delay...

>

> §4/rfc8126 presents some general arguments for creating registries.

> But let's talk about this specific case.

>

>

> I'm taking the liberty of summarizing your message this way:

>

> > Historically, we have created IANA registries for identifiers which are

> > likely to be needed by a variety of unrelated features supported by the

> > protocol. The expectation in these cases is that multiple documents -

> > largely unrelated to each other - might need to allocate an ID from the

> same

> > space.

> ...

> > What we have NOT done, historically, is create a registry for a flags field

> > which is not provided as a general purpose mechanism, but is specifically

> > scoped for use only within the context of the feature which defined the

> > TLV/sub-TLV. (There are many examples.)

> >

> > It is expected in these cases that if an additional flag is required, that

> > it will be defined in a document directly related to the original feature –

> > either a bis version of the original document or a new document which is

> > marked specifically as an update to the original document.

>

>

> In general, the expectations about the future use of a specific field

> (as you describe them) are not always obvious to the casual reader[*].

> If the intent was clear, and the expectation ("bis...an update") is

> spelled out in the document then I would not ask about the management

> of the bits.  And even better, future specifications (when maybe none

> of us are around anymore) would have clear guidance.

>

> Having said that, and knowing that I am not the responsible AD for lsr

> anymore, I would be very happy if the WG decided on requiring future

> documents to be clear about the intended use and any requirements for

> the allocation of flags or other unassigned bits.

>

>

> Thanks for starting this discussion!  I hope to see other opinions.

>

> Alvaro.

>

> [*] Anyone else besides maybe the authors themselves, including me.

>

>

>

> > Alvaro -

> >

> > In your review of draft-ietf-lsr-isis-srv6-extensions you requested the

> > authors to

> >

> > "Please ask IANA to set up a registry for the Flags."

> >

> > in multiple cases e.g., the flags field defined in the new SRv6 Capabilities

> > sub-TLV.

> >

> > This isn't the first time you have made such a request (I believe I argued

> > against this in the past and you relented – but only temporarily it seems.

> 😊

> > ).

> >

> > As it is a deviation from historical practice, I think it would be better if

> > the WG discussed whether there is a good reason to change our practices

> > rather than have this request be made based on the personal preference

> of the

> > current AD.

> >

> > Historically, we have created IANA registries for identifiers which are

> > likely to be needed by a variety of unrelated features supported by the

> > protocol. The expectation in these cases is that multiple documents -

> largely

> > unrelated to each other - might need to allocate an ID from the same

> space.

> >

> > Obvious examples are TLV/sub-TLV code points.

> >

> > In the case of flags, there are currently only two such registries:

> >

> > link-attribute bit values for sub-TLV 19 of TLV 22

> > (https://www.iana.org/assignments/isis-tlv-codepoints/isis-tlv-<https://www.iana.org/assignments/isis-tlv-codepoints/isis-tlv-codepoints.xhtml#isis-tlv-codepoints-19of22>

> codepoints.xhtml#isis-tlv-codepoints-19of22<https://www.iana.org/assignments/isis-tlv-codepoints/isis-tlv-codepoints.xhtml#isis-tlv-codepoints-19of22>)

> >

> > Bit Values for Prefix Attribute Flags Sub-TLV

> > (https://www.iana.org/assignments/isis-tlv-codepoints/isis-tlv-<https://www.iana.org/assignments/isis-tlv-codepoints/isis-tlv-codepoints.xhtml#prefix-attribute-flags>

> codepoints.xhtml#prefix-attribute-flags<https://www.iana.org/assignments/isis-tlv-codepoints/isis-tlv-codepoints.xhtml#prefix-attribute-flags>)

> >

> > In both of these cases the sub-TLVs were defining a general purpose bit

> > field. It was expected (and it has happened) that unrelated documents had

> a

> > need to allocate a bit in these fields.

> >

> > What we have NOT done, historically, is create a registry for a flags field

> > which is not provided as a general purpose mechanism, but is specifically

> > scoped for use only within the context of the feature which defined the

> > TLV/sub-TLV. (There are many examples.)

> >

> > It is expected in these cases that if an additional flag is required, that it

> > will be defined in a document directly related to the original feature –

> > either a bis version of the original document or a new document which is

> > marked specifically as an update to the original document.

> >

> > Management of the flag space in such cases has never required the

> overhead of

> > a registry.

> >

> > You seem to want to change that and I would like to know why?

> >

> > What problem exists that you are trying to solve?

> >

> > IMO, such a policy is not needed, does not add value, but does add

> additional

> > overhead to what is already a considerable set of hoops which drafts must

> > navigate on their way to becoming an RFC.

> >

> > The number of existing TLV/sub-TLVs which have flags fields is significant –

> > and the lack of a registry for these fields has not yet caused any problem.

> >

> > Appreciate if we could have open discussion on this.

> >

> > Les
_______________________________________________
Lsr mailing list
Lsr@ietf.org<mailto:Lsr@ietf.org>
https://www.ietf.org/mailman/listinfo/lsr