QoS Prioritisation using DSCP/DiffServ with Linux and XS708Ev2

Hello,

I'm trying reduce the mean-delay (round-trip-time) of my PTP packets when going over a switch and generated traffic by increasing the DSCP priority - but without success so far.

I have a XS708Ev2 and two types of data

• low priority iperf data with 9k packet size
• high priority PTP multicast data with about 100 byte packet size

I ve set the QoS of the XS708Ev2 to "802.1p/DSCP-based" (which was the default) - see attached screenshot.

Further more I ve set the DSCP field of the multicast traffic on both - sender and receiver - to CS5:

• sudo iptables -t mangle -A POSTROUTING -d 224.0.0.0/4 -j DSCP --set-dscp-class cs5

I'm not using 802.1p - so there is no VLAN tag which could overrule the DSCP value.

I verified this by wireshark:

• low priority (CS0) iperf data
  
• high priority (CS5) multicast PTP data
  
  

Is there something wrong with my approach - or is there another setting to enable QoS in the Switch?

I ve seen other configuration menus, which have some CoS sub-menus under QOS - but in my case only the port-based or DSCP-based setting is selectable - is this enough to get it working?

Thanks a lot in advance,

Karl