Re: [Int-area] [EXTERNAL] Re: IP parcels

[Toerless Eckert <[e-mail]>]

On Tue, Feb 01, 2022 at 08:14:08PM +0000, Templin (US), Fred L wrote:
> > Section 5 of draft-templin-intarea-parcels-06 reads as if there is a mandatory
> > dependency against draft-templin-6man-omni.
> > Q1: Is that true ? If not, then i must be overlooking a description how parcels would work
> >     in the absence of OMNI.
> 
> IP parcels are packets that both set a non-zero IP {Total, Payload} Length value and
> also include a Jumbo Payload option. By RFC2675, this constitutes an illegal jumbo
> and so it is highly unlikely that any native links (let alone native paths) would pass
> the Parcel unless it was first encapsulated. So, encapsulation is required in any case,
> and OMNI encapsulation is the prime example given. But, it is possible that some
> other form of encapsulation besides OMNI might pick up on the concept.

Thanks. I would strongly suggest to improve the text so that it does not look as
if parcels depend solely on an individual submission draft - but instead describe
the dependencies against the underlying layer.

For once, its not clear to me if/why those parcles could not simply be passed over any
link-layer that can support frames large enough for a parcel. Likewise, if the parcel
needs to be hop-by-hop segmented to fit smaller link layer size, a discussion about
the benefits and downsides of that adaption would certainly be useful for the document.

> > Q2: If there is this dependency, how do you think the parcel draft could go to
> >     standard given how OMNI is individual submission.
> 
> I haven't really thought about that much yet but I don't think OMNI needs to be
> a normative dependency; some other form of encapsulation might decide to
> pick up on the parcel concept in the future.

See above.

> > Q3: Is it possible for parcel support to only exist on an initial sequence of
> >     subnets, and as soon as a parcel packet has to be sent out to an interface
> >     that does not support parcels, the parcel is fragmented into normal/non-parcel
> >     IP packets ?
> 
> The parcel can only travel as far as the extent of the encapsulation, and once the
> encapsulation header is removed the only choices are: 1) deliver the parcel to
> upper layers in the case of local delivery, 2) insert a new encapsulation header
> (i.e., re-encapsulate) and forward the parcel further, or 3) unpack the parcel and
> forward each segment separately as an independent IP packet toward the final
> destination.

I think your 3) is what i was asking, and i don't see this explicitly written up
in the document.

> I had not really thought about case 3), and I will have to drop back and consider
> whether that is something we would want to support. And, I think this only applies
> for the final leg of the path from the decapsulator to the final destination and the
> same logic cannot be applied for the initial leg of the path from an original source
> to a first encapsulating node.
> 
> What do you think?

If a path from a parcel capable source to a non-parcel capable destination could
consist of a sequence of one or more subnets thart can carry parcels, ending in a
router that performs 3), aka: extracting the segments and passing them on as normal
IP packets over one or more subnets up to the final destination.

That sounds like the most obvious incremental deployment option.


Btw: this where just questions i stumbled across. I still haven't gotten to the point
of understanding what would be the benefit of parcels to existing network hops
except if there was a clear understanding that packets >> 64kb would create some
form of benefit for routers/network paths. But as far as i understood the document and
discussion on the mailing list, you where primarily looking for performance benefits
on the sending host though, not the network path. 

Cheers
    Toerless