[bess] CW in EVPN: Was Signaling Control Word in EVPN

[James Bensley <[e-mail]>]

Hi All,

I've removed all the individual contacts as per mod request and
changed the subject as this conversation was diverging away from the
OPs original query (sorry if any of that was my fault).


On Tue, 9 Oct 2018 at 15:54, Andrew G. Malis <[e-mail]> wrote:
>
> James,
>
> Agreed. We touched on that in section 7 of draft-ietf-pals-ethernet-cw, where we advised operators that enabling post-CW DPI for ECMP calculations could cause misordering.

Hi Andy,

Perhaps I wasn't clear enough - and LSR (not the ingress/egress LER)
even trying to detect CW is a source of problems within the network,
this is why I was querying the use of the PWMCW.


On Tue, 9 Oct 2018 at 16:44, Yutianpeng (Tim) <[e-mail]> wrote:
>
> Personally I support having control word capability which is more common. It is said in RFC 8214:
>
>    “It is recommended that the control word be included in the absence of an entropy label”
>
> So I think we can still have EL capability on EVPN VPWS if I understand correct. Only if the existing "BGP Path  Attributes" does not work well.
>
> I support adapt CW capability into EVPN also as EVPN itself is facing same challenge with EVPN VPWS.
>
> By the way, rfc4385 mentioned PW controlling ECMP.

The CW doesn't control ECMP - this is my gripe here. It's one thing to
recommend a technology that not all devices support (EL/ELI or FAT)
but which fully fixes the problem if it supported, it's another thing
to recommend a technology that doesn't fully fix the problem if it is
supported at all. My concern is that by continuing to suggest a
partial solution (PWMCW) we help to keep that partial solution in
circulation when surely the WG should look to deprecate it for a
solution that fully fixes the problem?

Cheers,
James.