Subject: [Pals] draft-ietf-pals-ethernet-cw Operational Considerations

From: Stewart Bryant <[email-masked]>
Date: Fri, 23 Feb 2018 16:01:58 +0000

I have edited the Operational Considerations section of 
draft-ietf-pals-ethernet-cw. Hopefully, I have correctly reflected our 
discussion at the last IETF.

Any comments before I upload a new version of the draft?

- Stewart

# Operational Considerations

CW presence on the PW is controlled by the configuration and may be subject
to default operational mode of not being enabled. Care needs to be taken
to ensure that software that implements this recommendation does not
depend on existing configuration setting that prevents the use of
control word. It is recommended that platform software emits a
rate limited message indicating that CW  can be used but is disabled
due to existing configuration.

Instead of including a payload type in the packet, MPLS relies on
the control plane to signal the payload type that follows the
bottom of the label stack. Some LSRs attempt to deduce the packet
type by MPLS payload inspection, in some cases looking past the
PW CW. If the payload appears to be IP or IP carried in an Ethernet
header they perform an ECMP calculation based on what they assume
to be the five tuple fields. However deduction of the payload type
in this way is not an exact science, and where a packet that is not
IP is mistaken for an IP packet the result can be packets delivered
out of order.
Misordering of this type can be difficult for an operator to dignose.
Operators therefore need to careful when enabling capability that
allows information gleaned from packet inspection past the PW CW to
be be used in any ECMP calculation.

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