cisco qos end to end question

[cormon]

hi guys

I am currently studying up on qos and think I've nailed the different options . My only stumbling block is where to place the actual qos rules


server

http://www---100m---router1---1.5m--router2--100m---userlan1

server dns
server sql



I read somewhere that the "qos should be placed close to the source facing the bottleneck close to the servers youre trying to ensure bandwidth to" , in this case SQL. Do I configure qos on router 1 and place it on the low bw link to router 2.

Do I also need to have qos configured on router 2 to ensure return traffic is priority on the return path.

I dont have any running config to post just trying to get the concept right.

Thanks in advance

 

[KiscoKid]

Typically you "mark" your traffic as close to the source as possible. By marking, I mean you assign an IP precedence or DSCP value to the traffic you want to define a QoS policy for.

Once marked, you can then assign bandwidth reservations on the bottlenecks in your network - typically WAN interconnections.

So in your scenario, I would assume you have a switch between all these servers and router 1? If so, you can mark the traffic on this device. Router 1 can then be configured to ensure the marked traffic receives the service (i.e. bandwidth reservation) you want.

And yes I would also prioritise the return traffic on router 2.

There's a few options available to you regarding how to configure this solution. It largely depends on the applications in use, their perceived importance and required priority levels.

The following is a comprehensive list of QoS mechanisms available. They include explations and configuration examples - they may prove of use to you:

http://www.cisco.com/en/US/tech/tk543/tsd_technology_support_category_home.html

 

[cormon]

Typically you "mark" your traffic as close to the source as possible. By marking, I mean you assign an IP precedence or DSCP value to the traffic you want to define a QoS policy for"

1)Can I also do this on the router itself instead off the switch .

2) Can I "mark" the traffic with an access-list.

thanks for the reply kiscokid.

Kevin.

 

[KiscoKid]

You can mark on the router for sure. The only thing to bear in mind is that your QoS solution would no longer be end-to-end and thus within your switching infrastructure, you will be just employing best-effort approach to QoS.


You can mark the traffic with an access list. The access list will allow you to identify the layer 3 or layer 4 characteristics of the applications in question. You could also entertain enabling something like NBAR which looks packets at an application layer and classifies them accordingly.

 

[cormon]

thanks again KiscoKid

exactly what I looking for.clear and concise.

One final point though. The three device are on a fullduplex 100m lan interfaces . is there need for qos here ? .My assertion was that the only on bottlenecks/aggregation links would qos be neccasary. BTW its a layer 2 switch.

Kevin

 

[KiscoKid]

I would agree that on your bottlenecks is the only likely place where you want to apply bandwidth reservations. On your faster, 100mb LAN (ingress) interfaces however you may want to classify/mark your traffic prior to that traffic hitting the WAN interface.

Whilst layer 2 switches don't understand IP Precedence, they may still be able to mark CoS (class of service). These bits in the frame correlate with the appropriate IP precedence hits hence your routers will still be able to understand the QoS markings.

Hope this helps.