Mls qos map cos dscp

Introduction

Objective

As a network engineer working for a Service Provider, configure Traffic Classification in a Converged network. The traffic types that need classification are: VOIP, Television, High-Speed Internet, and management traffic. But first the configuration has to be tested in a lab.

Note that the traffic types used are the same as the previous lab, where we assumed the classification has been done. In this lab we are doing the classification.

Testing Cases

For the lab the traffic sources are connected to NYCORE1. The service provider decided to classify traffic at the ingress of ports connected to the traffic sources. See the table below for the ports numbers and COS class.

Lab Network Diagram

Task Index

· Task 1 - Enable QoS. 


· Task 2 - Configure Classification at the Interface Ingress of the Traffic 


· Task 3 - COS-DSCP mapping 


· Task 4 - DSCP-COS mapping 


Task 1 - Enable QoS

Step 1: Access Switch NYCORE1 go to privileged mode

NYCORE1> enable

NYCORE1#

Step 2: Enable QoS on the switch

NYCORE1#config t

Enter configuration , one per line. End with CNTL/Z.

NYCORE1 (config)#mls qos

NYCORE1 (config)#

Step 3: Show that the QoS was enabled

NYCORE1(config)#exit

NYCORE1#show mls QoS

QoS is enabled
QoS ip packet dscp rewrite is enabled

Task 2 - Configure Classification at the Interface Ingress of the Traffic

The classification will be based on the layer 2 classification using COS. The Ethernet header has a 3 bits field that will carry the classification, the same way it carries source or destination mac address.

Step 1: Apply the classification on the interfaces

NYCORE1#Config t

NYCORE1(config-if)#int fa1/0/5

NYCORE1(config-if)#mls qos cos 6

NYCORE1 (config-if)#mls qos cos override

NYCORE1(config-if)#int fa1/0/6

NYCORE1(config-if)#mls qos cos 5

NYCORE1 (config-if)#mls qos cos override

NYCORE1(config-if)#int fa1/0/7

NYCORE1(config-if)#mls qos cos 3

NYCORE1(config-if)#mls qos cos override

NYCORE1(config-if)#int fa1/0/8

NYCORE1(config-if)#mls qos cos 0

NYCORE1 (config-if)#mls qos cos override

Step 2: Verify the configuration using the show run command

NYCORE1# show run

Scroll down using the space bar and you should see the interfaces configured as the following:

interface FastEthernet1/0/5

mls qos cos 6

!

interface FastEthernet1/0/6

mls qos cos 5 !

interface FastEthernet1/0/7

mls qos cos 3

!

interface FastEthernet1/0/8

Note that interface 1/0/8 does not show the COS, that is because the COS that was used for internet was COS 0, and that is the default. The show command does not show the default configuration on the Cisco switch.

Task 3 - COS-DSCP Mapping

Now that the traffic has been classified, we need to make sure, that the marking is done at the egress of the router toward the IP network, which uses Layer 3 DSCP marking. In production the backbone is based on other technologies and not Ethernet, so the layer 2 COS marking cannot be used. Layer 3 DSCP (Differentiated Services Code Point) is used. DSCP has 64 classes, from 0 to 63. So we need to map the COS marking to DSCP marking before it egress toward the backbone network. Cisco has already a default mapping, we will check it next.

Step 1: Show the default cos-dscp mapping

NYCORE1#show mls qos map cos-dscp

Cos-dscp map:

cos: 01234567 -------------------------------- dscp: 0 8 16 24 32 40 48 56

NYCORE1#show mls qos map cos-dscp

Cos-dscp map:

cos: 01234567 -------------------------------- dscp: 0 8 16 24 32 40 48 56

The output form the show command shows that all the COS classes are mapped, starting from COS 0 mapped to dscp 0 and ending with COS7 mapped to dscp 56.

Everything looks good except that in the case of this service provider you are working for, and as an example, dscp 40 is used from for something else, so you need to change the default mapping to map COS 5 to dscp 46 and not 40 as the default mapping. You will do that next.

Step 2: Change the default cos-dscp mapping

NYCORE1# config t

NYCORE1(config)#mls qos map cos-dscp 0 8 16 24 32 46 48 56

NYCORE1(config)#exit

Step 3: Verify the cos-dscp mapping changes

NYCORE1#show mls qos map cos-dscp

Cos-dscp map:

cos: 01234567 -------------------------------- dscp: 0 8 16 24 32 46 48 56

The output now shows that COS 5 is mapped to dscp 46.

Task 4 – DSCP-COS Mapping

The last switch before the customer connection in a production service provider network has to reverse the mapping from dscp to cos, since the customer is connected using fast Ethernet, which is a layer 2 protocol and does support cos. In the case of our lab NYCORE2 needs to do this mapping. But first let see what is the default Cisco dscp to cos mapping?

Step 1: Check the default dscp-cos mapping

Go to NYCORE2 and issue the following command:

NYCORE2#show mls qos map dscp-cos

Dscp-cos map:

d1: d20 1 2 3 4 5 6 7 8 9 ---------------------------------------

. 0: 00000000 


. 1: 01010101 


. 2: 02020202 


. 3: 03030404 


. 4: 05050505 


. 5: 06060606 


. 6: 07070707 


000000000101 010102020202 030303030303 040404040404 050505050606 060607070707

Because now we have to map 64 dscp classes to 8 cos classes, more than one dscp class can be mapped to one cos class.

In the output above d1 column represents the first digit of dscp, and d2 row represents the second digit. The cross point of d1 and d2 is the cos class. So for example dscp 21 is mapped to cos 2. We are interested in dscp 46, we want to make sure is mapped to cos 5, which is the reverse of what we did in TASK 3, Step 3.

So looking at dscp in the above output you can see that dscp 46 is mapped to cos 5, and all the other dscp that we are interested in are mapped to the right cos. Therefore you keep the dscp- cos default mapping.

With this we are sure that QoS classification and marking are kept end to end in the network.

Summary

In this lab you completed the following tasks:

· Task 1 - Enable QoS. 


· Task 2 - Configure Classification at the Interface Ingress of the Traffic 


· Task 3 - COS-DSCP Mapping 


· Task 4 - DSCP-COS Mapping 


NETW320 Week 2 Report

Configuring Traffic Classification (40 points)

Name:
Date:
Professor:

Write a paragraph (minimum five college-level sentences) below that summarizes what was accomplished in this lab. What did you learn by performing it? (10 points)

Answer the following question with short answers, and copy and paste the screenshots or the show output command when it is required, from the configuration.

*Hint* Read and study the instructions and explanations within the lab for assistance.

1. What was accomplished in task 2, step 1? (3 points)

2. What was accomplished in task 3, step 2? (3 points)

3. What was accomplished in task 4? (4 points)

4. Copy and paste the output from the show run that shows the interfaces configured with cos task 2, step 2. (5 points)

5. In the output of task 2, step 2, why is the cos 0 is not showing? (5 points)

6. Copy and paste the output from the show command in task 3, step 3. (5 points)

7. In the output of task 3, step 3, to which cos is dscp 46 mapped? (5 points)