Re: [Ila] Proposed charter

[Tom Herbert <[e-mail]>]

On Wed, Feb 7, 2018 at 8:43 AM, Alexandre Petrescu <
[e-mail]> wrote:

>
>
> Le 04/02/2018 à 00:44, Dino Farinacci a écrit :
>
>>
>> Hi Dino,
>>>
>>> Sorry not to get back to you sooner.
>>>
>>> On 19 January 2018 at 05:45, Dino Farinacci <[e-mail]>
>>> wrote:
>>>
>>>> The ILA domain is effectively a virtual link layer or an
>>>>>> underlay network for the traffic being carried between hosts
>>>>>> outside of the ILA domain. As long as the ILA domain is
>>>>>> perfectly transparent to the overlay network and its hosts,
>>>>>> then what ever happens within the ILA domain doesn't matter, similar
>>>>>> to how link layer compression, as long as fully and
>>>>>> perfectly reversed, also doesn't matter.)
>>>>>>
>>>>>
>>>> Mark, it was interesting the way you worded this. I think of ILA
>>>> and “its domain” as the overlay and once the originated packet is
>>>> transformed, it traverses the underlay.
>>>>
>>>>
>>> It has a few years since I read through Tom's initial ILA draft,
>>> and I'd forgotten a fair amount, in particular about the ILA
>>> address transform happening on the same device that originated the
>>> pre-ILA packet.
>>>
>>
>> But I think you got it right.
>>
>> The thing I remembered was that it could be described as
>>> "encapsulationless" tunnelling, where tunnel end-points are represented by
>>> /64s rather than /128s, and the address information that is normally
>>> preserved in the inner packet header is instead preserved in the ILA
>>> ingress and egress devices in the /64 mapping tables. It isn't perfect
>>> tunnelling though, as the hop count, DSCP
>>> and possibly the flow label field values are not preserved.
>>>
>>
>> Encapsulation-less is the right term. Meaning ILA puts no new headers
>> on the packet. It changes the source and destination high-order bits
>> in the packet. So the ID is perserved through the whole path.
>>
>
> I think encapsulation w/o new headers is better named 'address
> translation' rather than 'encapsulation-less' because there is no
> encapsulation at all.
>
> There is also 'Routing Header' that does not put new headers on the
> packet. (the RH is there but the nodes rotate somehow the addresses inside).
>
> Also, translation of addresses that is not evil is the NPT: Network Prefix
> Translation RFC.
>

I like Mark's explanation that ILA is "address transformation" not "address
translation". Maybe "zero packet overhead" is  better than
"encapsulation-less" to capture the property that ILA doesn't require
anything additional to the existing IP header?

Tom