Cisco PIX 525 Dokumentacja Pobierz pdf (Strona 323)

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Cisco Security Appliance Command Line Configuration Guide

OL-6721-01

Chapter 20 Applying QoS Policies

Activating the Service Policy

Viewing QoS Priority-Queue Statistics

To view the QoS priority-queue statistics, use the following command in privileged EXEC mode:

hostname# show service-policy priority

This command displays the QoS priority-queue statistics; for example:

hostname# show service-policy priority

Global policy:

Service-policy: global_fw_policy

Interface outside:

Service-policy: qos

Class-map: TG1-voice

Priority:

Interface outside: aggregate drop 0, aggregate transmit 9383

Note “Aggregate drop” denotes the aggregated drop in this interface; “aggregate transmit” denotes the

aggregated number of transmitted packets in this interface.

Activating the Service Policy

The service-policy command activates a policy-map command globally on all interfaces or on a targeted

interface. An interface can be a virtual (vlan) interface or a physical interface. Only one global

policy-map is allowed. If you specify the keyword interface and an interface name, the policy-map

applies only to that interface. An interface policy-map overrides a global policy-map, and only one

policy-map is allowed per interface. In general, a service-policy command can be applied to any

interface that can be defined by the nameif command.

Using the policy-map example in the previous section, the following service-policy command activates

the policy-map “qos,” defined in the previous section, for traffic on the outside interface:

hostname# service-policy qos interface outside

Applying Low Latency Queueing

The security appliance allows two classes of traffic: low latency queuing (LLQ) for higher priority,

latency-sensitive traffic (such as voice and video) and best effort, the default, for all other traffic. These

two queues are built into the system. The security appliance recognizes QoS priority traffic and enforces

appropriate QoS policies.

Because queues are not of infinite size, they can fill and overflow. When a queue is full, any additional

packets cannot get into the queue and are dropped. This is tail drop. To avoid having the queue fill up,

you can use the queue-limit command to increase the queue buffer size.

You can configure the low latency (priority) queue to fine-tune the maximum number of packets allowed

into the transmit queue (using the tx-ring-limit command) and to size the depth of the priority queue

(using the queue-limit command). This lets you control the latency and robustness of the priority

queuing.

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