QOS planning stage

Unanswered Question
Apr 3rd, 2008

Alrighty, Im in the planning/researching stage of a qos rollout. Im not sure if I should get a consultant to get it done within a day or try it myself and learn a thing or two. Im new to qos and read alittle so far from the manuals downloaded off the site. It seems there are a few options to choose from, thinking of going w 802.1p w diffserv, is this a good option? And before implementing I just wanted to get some opinions or hints.

Anyway, this is what Im working with:

-approx 100 nodes

-catalyst 4503 supII+TS

-trunk to catalyst 3560

-aironet 1200s

-vlan bw 4503 and asa

-vlan for video conference devices, want highest priority

-vlan for infrastructure, next priority

-vlan for managed wired access, next priority

-vlan for managed wifi access, next priority

-vlan for guest wired access, next priority

-vlan for guest wifi access, lowest priority

Just so you know this is a higher ed center, explains the guest access. Is there anyway to limit/lower the bandwidth for the guest vlans? When dealing with qos, is there any configuration that needs to be done on the actual end devices ie video units and windows machines?

Any ideas or best practices? If more info is needed just shout. As usual, thanks for the comments. R

I have this problem too.
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pcarvill Thu, 04/03/2008 - 10:01


Rather than jumping into a technical conversation I think you need to define what you want to achieve in basic English (the tools will allow you to accomplish most things).

Do you have a problem to solve (Latency, slowness issues with applications)? Do you have a policy to enforce and what is it (Guests limited to 1 meg of bw)? Write down in basic English what you want to achieve and I'm sure we can find the commands to accomplish it.

Based on what you want to achieve you will see where your QoS policy needs to be applied. Generally not on the end devices, but could be that they do some default marking which needs to be taken into account.

If I have to define a QoS policy, I basically like to get an idea of all the traffic on the network and any current marking systems. Then define what needs to be achieved (including SLAs, etc) and then the config begins.


rhopkins_nci Thu, 04/03/2008 - 11:52

Well its nothing major like an SLA or policy, just personal preference I guess. What got me thinking of qos was when checking the call statistics on the video units, I noticed some jitter/latency issues. So I wanted to try and resolve that. And while I was at it, I wanted to make sure the guest access had the least priority and bandwidth if possible, if I could meter the guest vlans to 256K to 1meg, that would be great. Other than that, thats about all I know or was wanting. By the way, how can I check to see if there are any currently marked systems? Thanks for the help Paul.

pcarvill Sat, 04/05/2008 - 03:02

Since you are on a Campus network, I doubt you are running into congestion on the wire. I would look at an LLQ approach prioritising your media traffic and policing your guest vlans. All other traffic should fall into your default class.

In your approach think end-to-end. Mark and classify as close to the edge. Ensure QoS is configured on all devices.

Start a QoS Policy Document where you describe your traffic classes and marking scheme. This will allow you to modify your QoS config easlier going forward.

This is of course off the top of my head, but it's a good place to start.

James Hawkins Sun, 04/06/2008 - 01:06

The best document for understanding QoS is the Enterprise QoS SRND which is available at the url below:


It ontins many examples which can be adopted to meet your needs.

It does not include specific configs for guest networks but how you would handle these would depend upon a number of things including how the user is identified as a guest and allocated to a guest VLAN. In the past I have done this by using 802.1x and a radius server to allocate VLANs based upon login credentials.

With QoS I would probably not treat guests as any different to normal users on the LAN (allow them 5 Mbps of traffic before remarking everything else as scavenger). I wold enforce some form of rate limiting on Internet uplinks to ensure that guests do not consume all the bandwidth.

Before you get started I think that you need to define a QoS policy detailing your traffic classes and how traffic applied to them should be identified and marked. I would do this on the edge switches and definitley not trust markings you receive from end devices.


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