WRED drops packets
selectively based on
any specified criteria, such
as CoS, DSCP, EXP, discard-class, or precedence
. WRED uses
these
matching criteria
to determine how to treat different types of traffic.
Configure WRED using the
random-detect command and different CoS, DSCP,
EXP, and discard-class values. The value can be range or a list of values that
are valid for that field. You can also use minimum and maximum queue thresholds
to determine the dropping point.
When a packet arrives, the
following actions occur:
-
If the
queue size is less than the minimum queue threshold, the
arriving packet is queued.
-
If the
queue size is between the minimum queue threshold for that
type of traffic and the maximum threshold for the interface, the packet is
either dropped or queued, depending on the packet drop probability for that
type of traffic.
-
If the
queue size is greater than the maximum threshold, the packet
is dropped.
Restrictions
-
On systems with Cisco ASR 9000 High-Density 100GE Ethernet line cards and fifth-generation line cards, ensure that you configure
the minimum and maximum threshold values that are greater than the default minimum and maximum threshold values. If you apply
a policy that has lesser than default values to a bundle that has both these line cards, the show policy-map interface command displays a mismatch in statistics bag size.
-
When configuring the random-detect dscp command, you must configure one of the following commands: shape average, bandwidth, and bandwidth remaining.
Note
|
The Cisco ASR 9000 Series ATM SPA supports only time-based WRED thresholds. Therefore, if you try to configure the WRED threshold
using the random-detect default command with bytes or packet as the threshold units, the "Unsupported WRED unit on ATM interface" error occurs.
|
-
Only two minimum and maximum thresholds (each with different match criteria) can be configured per class.