Knowledge Base

Setting DSCP/QOS Byte on packets with Windows 7/8

Question

I'm trying to set the DSCP byte on packets and am getting an error (and it doesn't work!).

Solution

Important note: The following information currently only applies to versions 4.12.0 and older of PingPlotter.

Starting with Windows 7, it's more difficult to use application-set DSCP bytes on packets. The operating system wants to override the setting that PingPlotter uses. This results in all outbound packets being set with 0 (or some other OS-policy-defined) DSCP value.

It's difficult to work around this with Windows 7 / 8, and for best results, you might want to switch to using Windows XP for this type of testing.

Some of this depends on if you're part of a domain or not, and which edition of Windows you're using.

You may have working results by making a couple of registry changes. The settings here include any settings that PingPlotter tries to make itself, so if you're getting a permissions error when you try changing the DSCP setting in PingPlotter, you can follow these instructions as well.

To make changes to the registry which "might" allow custom DSCP values to work in Windows 7 / Windows 8:

• Download (and save) this .reg file.
• Extract the .reg file from the .zip. Launch the .reg file. Allow RegEdit to make the changes as prompted.
• Reboot.
• Make the changes in the DSCP field in PingPlotter Packet Options.

We've had success with the TCP packet type using Npcap on most editions of Windows, but not as much success with ICMP. Your results may vary.