DEI egress remarking

It is often desirable to meter traffic from different users to ensure fairness or to meet bandwidth guarantees. Dropping all traffic in excess of a committed rate is likely to result in severe under-utilization of the networks, because most traffic sources are bursty in nature. It is burdensome to meter traffic at all points in the network where bandwidth contention occurs. One solution is to mark those frames in excess of the committed rate as drop eligible on admission to the network.

Previously, the discard eligibility was determined using existing QoS fields; for example, the three MPLS EXP and Ethernet dot1p bits. Using specific combinations of these bits to indicate both forwarding class (priority) and discard eligibility meant decreasing the number of forwarding classes that can be differentiated in the network.

IEEE 802.1ad-2005 and IEEE 802.1ah standards allow drop eligibility to be conveyed separately from priority, preserving all the eight forwarding classes (priorities) that could be indicated using the three 802.1p bits. All the previously introduced traffic types are marked as drop eligible. Customers can continue to use the dot1p markings with the enhancement of changing the dot1p value used, in access, based on the profile information.

The following commands can be used to remark the DE values at a SAP egress:

sap-egress policy-id create
     fc fc-name create
           de-mark [force de-value]
           de-mark-inner [force de-value]
           de-mark-outer [force de-value]
     exit 
exit

By default, the DE bit is set to 0 for inplus-profile and in-profile traffic and 1 for out-of-profile and exceed-profile traffic, unless explicitly forced.

The precedence of these commands is summarized from highest to lowest precedence, as follows:

• de-mark-outer used for outer tag markings

• de-mark-inner used for inner tag markings

• existing de-mark used for marking both tags

• markings taken from packet received at ingress

The configuration of qinq-mark-top-only under the SAP egress takes precedence over the use of the de-mark-inner in the policy, that is, the inner VLAN tag is not remarked when qinq-mark-top-only is configured. The marking used for the inner VLAN tag is based on the current default, which is governed by the marking of the packet received at the ingress to the system. If qinq-mark-top-only is omitted, both the inner and outer VLAN tags are remarked.

Remarking the inner DE bit is not supported based on the profile result of egress policing.

The egress remarking occurs after any egress classification.