Re: [Ila] Proposed charter

[Mark Smith <[e-mail]>]

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.

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.

My default view of tunnelling is that it occurs somewhere within the
network.That means my default view of hosts is that they are simple,
meaning that they use the addresses they're given, the address(es) the
host has are the address(es) that are visible to applications and the
IP stack in the host below the application normally won't do anything
"complex" like ILA.

So from the perspective of the applications, ILA looks like something
that is occurring in the IP layer (either within the packet origin
device, or within a router along the path to the final destination),
and as an IP tunnel is a virtual link, and links appear below the IP
layer, that is why I described ILA as an underlay.

Regards,
Mark.





> Dino
>