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 <[email protected]> wrote: > On Tue, 9 Oct 2018 at 15:16, Andrew G. Malis <[email protected]> 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. >
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