CCNP ONT Exam Certification Guide

QoS Service Class (Classification, Marking, and NBAR)

Planning and implementing QoS policies entails three main steps: Step 1 Identify network traffic and its requirements. Step 2 Divide the identified traffic into classes. Step 3 Define QoS policies for each class. In Step 1, you use tools such as NBAR to identify the existing traffic in the network. You might discover many different […]

Trust Boundaries (Classification, Marking, and NBAR)

End-system devices such as personal computers, IP phones, IP conference devices, and video conference gateways, plus switches and routers at different levels of the network hierarchy, can mark the IP packets or the encapsulating frames such as 802.1Q/P. One of the design and policy decisions you have to make is where to place your network […]

Network Based Application Recognition (NBAR) (Classification, Marking, and NBAR)

NBAR is a Cisco IOS feature that can be used to perform three tasks: ■ Protocol discovery ■ Traffic statistics collection ■ Traffic classification Because NBAR can discover which applications and protocols are running on your network and display volume and statistics about them, you can use it as a powerful yet simple tool to […]

Cisco IOS Commands to Configure NBAR (Classification, Marking, and NBAR)

To enhance the list of protocols that NBAR recognizes through a PDLM, download the PDLM from CCO and copy it into the flash or on a TFTP server. Next, enter the following command, which refers to the PDLM name in URL format: The URL, for example, can be flash://citrix.pdlm, referring to the citrix.pdlm file in […]

Introduction to Congestion Management and Queuing

Congestion happens when the rate of input (incoming traffic switched) to an interface exceeds the rate of output (outgoing traffic) from an interface. Why would this happen? Sometimes traffic enters a device from a high-speed interface and it has to depart from a lower-speed interface; this can cause congestion on the egress lower-speed interface, and […]

First-In-First-Out, Priority Queuing, Round-Robin, and Weighted Round-Robin Queuing (Congestion Management and Queuing)

FIFO is the default queuing discipline in most interfaces except those at 2.048 Mbps or lower (E1). The hardware queue (TxQ) also processes packets based on the FIFO discipline. Each queue within a multiqueue discipline is a FIFO queue. FIFO is a simple algorithm that requires no configuration effort. Packets line up in a single […]

Weighted Fair Queuing (Congestion Management and Queuing)

WFQ is a simple yet important queuing mechanism on Cisco routers for two important reasons: first, WFQ is the default queuing on serial interfaces at 2.048 Mbps (E1) or lower speeds; second, WFQ is used by CBWFQ and LLQ, which are two popular, modern and advanced queuing methods. (CBWFQ and LLQ are discussed in the […]

Class-Based Weighted Fair Queuing (Congestion Management and Queuing)

CBWFQ addresses some of the limitations of PQ, CQ, and WFQ. CBWFQ allows creation of user-defined classes, each of which is assigned to its own queue. Each queue receives a user-defined (minimum) bandwidth guarantee, but it can use more bandwidth if it is available. In contrast to PQ, no queue in CBWFQ is starved. Unlike […]

Low-Latency Queuing (Congestion Management and Queuing)

Neither WFQ nor CBWFQ can provide guaranteed bandwidth and low-delay guarantee to selected applications such as VoIP; that is because those queuing models have no priority queue. Certain applications such as VoIP have a small end-to-end delay budget and little tolerance to jitter (delay variation among packets of a flow). LLQ includes a strict-priority queue […]

Congestion Avoidance

Congestion avoidance is used to avoid tail drop, which has several drawbacks. RED and its variations, namely WRED and CBWRED, are commonly used congestion-avoidance techniques used on Cisco router interfaces. Congestion avoidance is one of the main pieces of a QoS solution. Tail Drop and Its Limitations When the hardware queue (transmit queue, TxQ) is […]