ONT – Cong. Mgnt & Queu. Pt. 1
What interface configuration command sets the size of the hardware queue of an interface?
What command can be used to display the size of the hardware (transmit) queue on serial interfaces?
show controllers serial
Describe how a first-in, first-out queuing works on an interface.
FIFO is the default queuing discipline in most interfaces except those at 2.048 Mbps or lower (E1). FIFO is a simple algorithm that requires no configuration.
What are the 4 different queues available with Priority Queuing and how do they function.

PQ has four queues available:high, medium, normal, and low. As long as the high-priority queue has packets, the PQ scheduler forwards packets only from the high-priority queue. If the high-priority queue is empty, one packet from the medium-priority queue is processed. After processing-dequeuing one packet from any queue, the scheduler always starts over again at the top.

What command is used to define the traffic that is assigned to each of the 4 PQ queues?
priority-list list-num {protocol name | interface int | default} {high | medium | normal | low}
What command specifies the maximum number of packets allowed in each of the priority queues?
priority-list list-num queue-limit [high-limit [medium-limit [normal-limit [low-limit]]]
What are the default Priority Queuing packet limits?
From high to low, they are 20, 40, 60, and 80, respectfully.
What command assigns a priority list number to an interface?
priority-group list-num
What command displays the contents of packets inside a queue for a particular interface?
show queue interface
What command displays the status of the priority queuing lists?
show queueing priority
Describe how Round Robin queueing works as a queueing discipline.
RR has typically has a few queues, and you assign traffic to them. The RR scheduler processes one packet from one queue and then a packet from the next queue and so on. No queue has priority over the others, and if the packet sizes from all the queues are (roughly) the same, effectively the interface bandwidth is shared equally among the RR queues.
How does Weighted Round Robin (WRR) differ from just Round Robin?
WRR allows you to assign a "weight" to each queue, and based on that weight, each queue effectively receives a portion of the interface bandwidth, not necessarily equal to the others.
Baed on what fields can the flows of WFQ be identified?
Flows are identied based onthe following fields from IP and either TCP or UDP headers: – Source or destination IP address – Source or destination TCP/UDP port number – Protocol number – Type of service (ToS)
How are hashes used with WFQ to determine what queue a packet should go in?
A hash is generated based on the fields in the IP and transport headers.

Because packets of the same traffic flow end up with the same hash values, they are assigned to the same queue. If the packet is the first from a new flow, it is assigned to a new queue for that flow.

In WFQ, describe how an assigned sequence number is used for scheduling purposes.
Every packet that arrives is assigned a sequence number and a queue.

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The sequence number is determined by multiplying the weight (which is inversely proportional to the packet priority (ToS)) by the packet size. Then the sequence number of the last packet in the flow queue is added to this modified size.

How do you construct the queues to be used in WFQ?
The WFQ system is based on the number of active flows, so WFQ dynamically builds and deletes queues. The interface bandwidth is divided among the active flows/queues, and that division is partially dependent on the priorities of those flows. So WFQ does not offer precise control over bandwidth allocation among the flows.
How does WFQ work with tunneling and encryption?
WFQ does not work with tunneling and encryption, because WFQ needs access to packet header fields to compute the hash used for assigning packets to flow-based queues.

How many flows/queues can be build by the WFQ system?
The maximum number of queues, called WFQ dynamic queues, is 256 by default. The number can be set between 16 and 4096, but the number must be a power of 2.
What command enables WFQ on an interface?
fair-queue [cdt_theshold [dynamic_queues [reservable-queues]]]
What command modifies the number of packets an interface can hold in its outbound software queue when using WFQ?
hold-queue max-limit out
What command displays information out the WFQ system on a particular interface?
show queue interface