What type of trust configurations do Catalyst switches support on ingress frames.

Catalyst switches support trusting via DSCP, IP Precedence, or CoS values on ingress frames. When trusting CoS or IP Precedence, Catalyst switches map an ingress packet's CoS or IP Precedence to an internal DSCP value.

Describe how the default CoS-to-DSCP and IP Precedence-to-DSCP mappings are configured.

For each value bit that is set on CoS or IP Precedence, a value of (value * 8) exists for DSCP

What command configures a switch for trusting using DSCP, CoS, or IP Precedence?

What command configured CoS-to-DSCP mapping on a switch?

What command configures IP Presedence-to-DSCP mappings on a switch?

What type of classification features are supported by NBAR?

- Classification of applications that dynamically assign TCP and UDP ports.

 

- Classification of HTTP traffic by URL, host, or MIME type

 

- Classification of Citrix Independent Computer Architecture (ICA) traffic by application name

 

- Classification of applications using subport information 

Describe how marking works in regards to QoS

Marking refers to changing the DSCP, CoS, or IP Precedence bits on ingress frames. Marking is configurable on a per-interface basis or via a policy map. Marking alters the DSCP value of packets, which in turn affects the internal DSCP.

What command configures DSCP marking on the ingress queue of a switch?

What command configured CoS marking on the ingress queue of a switch?

Describe how shaping works with regards to traffic conditioning

Shaping meters traffic rates and delays (buffers) excessive traffic so that the traffic rates stay within a desired rate limit. As a result, shaping smoothes excessive bursts to produce a steady flow of data.

Describe Policing with regards to traffic conditioning.

Policing does not delay or buffer traffic. The action for traffic that exceeds a specified rate is usually to drop.

What is a leading recommended formula for configuring traffic bursts?

What are the 3 different types of traffic policing on Catalyst switches?

Individual policers, aggregate policers, and microflow policing

Describe the individual policers type of traffic policing on Catalyst switches.

An individual policer is a per-interface policer where the switch applies specified policing parameters on a per-interface basis.

Describe the aggregate policers type of traffic policing on Catalyst switches.

Microflow policing is a per-flow policing where a switch applies policing parameters to each class within a policy map

What command configures the DSCP-to-CoS mapping on a switch?

Explain the specific nomenclature for referencing egress queues in Cisco IOS.

Describe the FIFO queuing method on a switch.

FIFO queuing is the default method of queuing, in which the switch places all egress frames into the same queue. FIFO queuing does not use classification, and all packets are treated as if they belong to the same class.

Describe the Weighted Round Robin (WRR) queuing method on a switch.

Describe the shaped mode for the Shaped Round Robin (SRR) method of queuing.

In shaped mode, egress queues are shaped to an exact percentage of interface bandwidth. Traffic from an egress queue cannot exceed a specific rate regardless of traffic in other queues.

Describe the shared mode for the Shaped Round Robin (SRR) method of queuing.

In shared mode, egress queues receive a percentage of bandwidth; however, the egress queues are not limited to that bandwidth. Queues are able to use bandwidth from other queues if their queues do not have data to transmit. Also, a percentage of bandwidth per queue is guaranteed when congestion exists.

Describe the priority queuing method of traffic shaping

When applying priority queuing to egress queues, the switch schedules frames from that queue as long as there are frames in the queue, before servicing any other queue.

Describe how Catalyst switches use Custom Queuing as a queuing method.

Custom queuing (CQ) reserves a percentage of available bandwidth for an interface for each selected traffic type. If a particular type of traffic is not using the reserved bandwidth, other queues and types of traffic may use the remaining babdwidth.

How does congestion avoidance work on a Catalyst switch?

Congestion-avoidance techniques monitor network traffic loads in an effort to anticipate and avoid congestion at common network bottleneck points.

Describe the tail drop behavior on a Catalyst switch.

If the arrival rate of packets for transmission on an interface exceed the router's or switch's ability to buffer the traffic, the router or switch simply drops the packets. This is the default behavior on Catalyst switches.

Describe how global synchronization effects traffic flows on a switch.

As a result of multiple TCP flows vastly exceeding the buffer limit, multiple TCP sessions simultaneously go into TCP slow start. Consequently, all TCP traffic slows down and then slow-starts again. This behavior occurs as waves of congestion crest only to be followed by thoughs during which link utilization is not fully utilized.

Describe how Weighted Random Early Detection (WRED) works as a congestion-avoidance mechanism.

WRED attempts to avoid congestion by randomly dropping packets with a certain classification when output buffers reach a specific threshold. RED randomly drops packets at configured threshold values (percentage full) of output buffers. As more packets fill the output queues, the switch randomly drops frames in an atempt to avoid congestion without the "saw-tooth" TCP problem.

What should be configured on all inter-switch links in the Building Distribution submodule?

In this layer, configure all inter-switch links for trusting. In this manner, the Building Distribution submodule switches trust the classification from all other switches.

What does AutoQoS use to ensure that the device attached to the LAN is really an IP phone?

AutoQoS used CDP for voice packets the ensure that the device attached to the LAN is really an IP phone

What are the 2 interface configuration options for enabling AutoQoS on Catalyst switches running IOS?

-  VoIP Cisco-phone - Trusts ingress CoS and DSCP only if a phone is detected and connected to the interface with CDP

What are the major configuration components for QoS on Catalyst switches?

- Congestion management and avoidance