Hello, can somebody explain me what is the idea of marking packets and how is it done. Does it have something in common with QoS?

"Marking" a packet allows that packet to be treated differently as it goes through your network depending on the marking. For example, you can mark a VoIP (Voice over IP) packet such that it gets priority over normal data traffic to provide it with a better Quality of Service (QoS).

A marking could be one of the following:

- CoS (Class of Service)
- DSCP (DiffServ Code Point)
- IP Precedence

The way you mark a packet depends on your network device (each vendor does it differently). But basically you first match a criteria (say VoIP traffic, or DNS, etc) and then you set the bits on the packet (again vendor specific) and then you pass it along with the set bits. Once you mark the packet then as the packet goes through the network each network element that receives the packet would have to look for the marking (i.e. the properly set bits) and act accordingly.

Hope that helps as a starting point.

Casey

Hi, thank you for answer - it was very helpful. But I have another question : you wrote that marking a packet depends on network device (different vendors), but there's many firewalls which offer marking packets. Do they have different implementations (for marking packets) for different devices?
How and where can I set bits on a packet if I want to mark it - in ethernet frame, ip packet header etc or in data field?

Thanks - mikkael

What I meant by vendor dependent is in the mechanics (command line, GUI, etc) they use to mark the packets. However, the result of what they do at the packet header level should be standard. Here is a quick reference on how QoS is done (high level) from Cisco:

http://www.cisco.com/en/US/products/...800a3e2f.shtml

Casey

Thanks - finally I had a chance to figure it out. Now I wonder how to implement this engine under windows (VS.NET), for example how to mark outgoing packets. I know that there is API for .NET - I have found some files in my .NET directory like "Qos.h", "QosName.h", "Qossp.h". Do how how to use this API or have example source?