Re: [bess] Signaling Control Word in EVPN

["Andrew G. Malis" <[e-mail]>]

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.

Cheers,
Andy


On Tue, Oct 9, 2018 at 10:35 AM James Bensley <[e-mail]> wrote:

> On Tue, 9 Oct 2018 at 15:16, Andrew G. Malis <[e-mail]> wrote:
> >
> > James,
>
> Hi Andy,
>
> > It's much harder to mandate use of EL than the CW for several reasons:
>
> I didn't say it should be mandated, but recommended.
>
> > - CW implementation is much more common than EL implementation
> > - PWs and/or EVPN are rarely the only traffic in an MPLS traffic tunnel,
> rather, they will be multiplexed with other MPLS-based applications that
> are using the traffic tunnel to reach a common destination. Thus, by using
> the CW, you can disable ECMP only for those MPLS packets that cannot
> tolerate reordering.
>
> The CW does not disable ECMP. Any LSR on the path between ingress and
> egress LER is free to look beyond the MPLS label stack and
> misinterpret the 0x00 0x00 at the start of a control-word as a valid
> MAC that starts 00:00:XX:XX:XX:XX and try to hash on Ethernet headers
> starting directly after the MPLS label stack, and not label stack + 4
> bytes. This is my point. The PWMCW doesn't stop re-ording in all
> cases, but it does in most. So yes, not all devices support EL, but CW
> doesn't stop re-ordering in all cases, so?
>
> > That said, I'm also concerned that because of the existing text in 7432,
> implementations may not be using the CW even for P2P EVPN.
> >
> > And we still don't have a good answer for Muthu's original question. :-)
>
> Sorry my intention is not to send this thread off-topic.
>
> Cheers,
> James.
>