CBWFQ Flashcards
How is WRED configured?
Using the random-detect command either on the interface or in a policy-map.
What type of queue is enabled when WRED is turned on?
FIFO.
How can you set the depth of the queue used for WRED?
hold-queue out.
Which values can be used to influence drop probability?
IPP or DSCP.
How can you ensure a particular marking never gets dropped?
Configure a min threshold that is greater than the hold queue depth.
What is the Mark Probability Denominator (MPD)?
An inverse value used to determine how many packets are dropped between the min and max thresholds.
If an MPD of 4 is used, 25% of packets for this marking will be dropped at the max threshold.
What is the Exponential Weighting Constant?
WRED does not act on actual queue depth but on an average queue depth. The EWC changes how quickly WRED reacts to the changing queue depth.
- 9 is the default. The valid range is 1-16.
- A lower number makes WRED react more quickly.
- A higher number makes WRED react more slowly.
How is the EWC configured?
random-detect exponential-weighting-constant
What is ECN mode?
If ECN is supported on a particular flow (signified by the ToS two least significant bits) the router may mark the packet with Congestion Encountered (CE) instead of dropping the packet. The receiver then echoes this back to the sender to ask it to slow down.
How is ECN mode configured?
random-detect ecn
What is flow mode?
When used on an interface only WRED can use flow mode to ensure flows are taken into account when dropping packets.
How can the amount of tracked flows be configured for flow mode?
random-detect flow count
How many packets can each flow have in flow mode?
The queue depth is divided by the number of flows and then multiplied buy the average depth factor which must be a power of 2.
random-detect flow average-depth-factor
