Catalyst 3560 Cisco IOS QoS.

Well, sometimes i feel like the best way to understand a technology is to write about it. I was reading about QoS for Cisco based switched networks and i though maybe i could share my understanding of the technology with all visitors of this blog.

Qos which is an abbr to "Quality of Serice" according to Cisco; refers to the capability of a network to provide better service to selected network traffic over various technologies, including Frame Relay, Asynchronous Transfer Mode (ATM), Ethernet and 802.1 networks, SONET, and IP-routed networks that may use any or all of these underlying technologies. The primary goal of QoS is to provide priority including dedicated bandwidth, controlled jitter and latency (required by some real-time and interactive traffic), and improved loss characteristics. Also important is making sure that providing priority for one or more flows does not make other flows fail. QoS technologies provide the elemental building blocks that will be used for future business applications in campus, WAN, and service provider networks. This chapter outlines the features and benefits of the QoS provided by the Cisco IOS QoS.

Now that we all know what QoS is, lets see how it can be implemented on a Cisco 3560 Catalyst layer 3 switch.

Will start by classifying the type of traffic or application we need to implement QoS on.

Router#enable
Router#config terminal
Router(config)#class-map match-any junk-internet-traffic
Router(config-cmap)#match protocol kazza2
Router(config-cmap)#match protocol Gnutella
Router(config-cmap)#match protocol fasttrack
Router(config-cmap)#exit

Router(config)#class-map match-any important
Router(config-cmap)#match protocol ipsec
Router(config-cmap)#match protocol smtp
Router(config-cmap)#exit

After classifying we now need to Mark the above applications/traffic.

Router#enable
Router#config terminal
Router(config)#policy-map marking
Router(config-pmap)#class junk-internet-traffic
Router(config-pmap-c)#set precedence 0
Router(config-pmap-c)#exit
Router(config-pmap)#class important
Router(config-pmap-c)#set precedence 5
Router(config-pmap-c)#exit

After Marking the traffic we can now apply the policy to the interface.

Router#enable
Router#config terminal
Router(config)#int fa0/0
Router(config-if)#service-policy input marking


With the above, we have achieved to implement QoS with one Policy called Marking which contains a number of different classes of traffic i.e. important and junk-internet-traffic.