Re: [tsvwg] I-D Action: draft-ietf-tsvwg-ecn-l4s-id-18.txt

[Derek Fawcus <[e-mail]>]

On Thu, Jul 01, 2021 at 01:45:05PM +0100, Bob Briscoe wrote:
>   * After consulting with the int-area
>     <https://mailarchive.ietf.org/arch/msg/int-area/y5UmhfSAka7xi_iBvX50bZ0jxzQ/>
>     and PALS
>     <https://mailarchive.ietf.org/arch/msg/pals/iWxEpj0MB-Du_U8KjelIocbg6Yk/>
>     lists (follow the links for the relevant long threads), it was
>     decided there is no need to mention that tunnels that support
>     resequencing like L2TP should have it disabled for data channels
>     carrying L4S traffic (because there's no evidence that any would
>     enable sequencing for IP data - sequencing is generally for the
>     tunnel control channel or for stateful header compression that
>     nowadays hinders rather than helps performance).

While that was the service provider view, it is not the only deployment
of L2TP.  So I'm not sure that this is a safe assumption, as one of the
cases I believe I mentioned in that thread is the Microsoft RAS VPN product.

It has at least two forms, PPTP (IP/PPP/GREv1) and L2TP/IPsec (IP/PPP/L2TP/ESP).
Both forms can make use of sequence numbers in their encapsulation.

I know the PPTP version is still actively being used, as we recently ended
up adding an ALG for it to our CGNAT software, due to requests.

We used to support use of the L2TP form in our product around 3 years ago,
so it was still in use then.  It could well still be in use, as it often
'just works' through NATs since its ESP has a version of UDP NAT-Traversal.

Last I played with these, the MS version offered the ability to enable
compression, which I believe included IP header compressions, and so may
be reordering sensitive.

The problem here would be in determining the degree of use, and if people
(usually not being specialists) have enabled compression.  Certainly one
place I worked at some years ago had enabled compression, that was by
someone who just viewed compression as good.  This was a SME, which seems
to be the usual use case.

DF