QoS på Cisco

[timtowtdi]

Skrev noe på en webside her, kanskje nyttig for noen:

 

Quality of Service

 

The two terms 'Quality' and 'Service' can be defined equivocal: Experienced / Expected

 

We want our customer to experience great service - we do The Traditional Approach: increase bandwidth - do The Flank Maneuver: upgrade some equipment - and finally accept that the fact is Lowered Expectations.

 

But what are really our customer's expectations?

 

In my world, customers expect connectivity and bandwidth around the clock. They expect certain bandwidth and low jitter for voice calls. Some want guaranteed bandwidth for video-conferencing traffic. One customer want 50Mbps uplink bandwidth to be available amd freely shared between five different sites, but with a certain level of guaranteed bandwidth available to each of the sites.

 

Being the messenger - we wash our hands for any dirt, aggressive protocols, spam, attacks - you name it we bring it as long as it has a IPv4 header. The traffic patterns seen can be a challenge. Links are frequently congested, UDP times out and TCP's backoff algorithm goes kanakkas - with the result that end-user experience no service - which is A Bad Thing® .

 

The solution to these issues on Cisco IOS is to use MQC to build class-maps and policy-maps and finally apply the service-policy on the interface. Frequently known as CBWFQ, this is also often a result of our activities in MQC

 

The key element is to make a parent-child class structure and traffic-shape in the parent class, while the traffic classes / PHBs (Per-Hop Behaviors) are defined in the child-structure.

 

Here is an example defining two classes, the VOICE class confirming 128kbps traffic to RFC3246, the VIDEO 512kbps to RFC2597. We use NBAR payload classification for simplicity:

 

class-map match-any VOICE

match protocol rtp audio

 

class-map match-any VIDEO

match protocol rtp video

 

policy-map CHILD

class VOICE

priority 128 3200

class VIDEO

bandwidth 512

class class-default

fair-queue

 

policy-map PARENT

class class-default

shape average 960000

service-policy CHILD

 

interface Serial0

service-policy output PARENT

 

 

Now if the Professor Balthazar Machine is working, you get some pretty nifty statistics and can tune your setup by issuing:

 

show policy-map interface

 

You can play with the whole MQC/CBWFQ shebang for many hours. I have done that. It boils down to the old principle KISS (Keep It Simple Stupid), if you must enable other mechanisms, I suggest random-detect on the default class within the CHILD structure. It drops packets and prevents packet loss in other classes.

 

timtowtdi

Endret 24. november 2008 av timtowtdi

[L4r5]

Veldig greit med en liten guide ja. Mange som sliter med QoS

 

Men burde kanskje vært plassert på Nettverk (bedrift)