DSCP marking by 3CX Phone System

[CedarglenHomes]

I have set MSRTPTOS to 46 and rebooted my 3CX server in an attempt to enable DSCP markings for call traffic leaving 3CX.

I then used tcpdump to create a pcap file with some call data in it to confirm MSRTPTOS is in effect and adding the DSCP markings.
However it does not appear to be adding the markings when reviewing the PCAP in wireshark.

What am I missing?

The 3CX server is running on linux.
I am currently on Version 16 and am fully up to date

Thanks

 

[cobaltit]

Not sure if you read the description but this appears to be a Windows-only setting and honestly I don't know if it works there.

This parameter instructs the Media Server to mark all the packets it generates with a value between 0 and 63 in the DSCP field in the IP Header. Default Value: 0 - Valid Values: 0-63 Please note that Windows XP and Server 2003 disables IP Header tagging by default. You will need to set a DWORD registry value called DWORD registry value called DisableUserTOSSetting in the following location "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters" and give it value "0". You will need to restart the machine for this setting to kick in.

Since you're on linux, follow this guide:

https://www.3cx.com/blog/voip-howto/qos-linux/

 

[complex1]

Yes it is possible to mark RTP traffic with DSCP 46 and mark SIP traffic with DSCP 26.
You have to add mangle rules to your iptables.

 

[CedarglenHomes]

Not sure if you read the description but this appears to be a Windows-only setting and honestly I don't know if it works there.



Since you're on linux, follow this guide:

https://www.3cx.com/blog/voip-howto/qos-linux/

I did read the description. It does not say the setting is windows specific. It says under windows XP or Server 2003 you have to enable aditional windows settings before it works correctly.

I did see the guide you linked to. however the mangle commands given as example don't work.

I did manage to find working examples in this thread about half way down that I was able to successfully implement

https://www.3cx.com/community/threads/ubiquiti-edgerouter-qos-with-3cx-softphones-question.67413/

These examples are better also in that they don't tag all traffic from the server just the appropriate voip traffic.

Thanks

 

[cobaltit]

Very true it doesn't say it's only for Windows (and neither did I) but keeping in mind that 3CX was originally Windows only coupled with the fact it's called MSRTPTOS leads me to believe it's a legacy setting that doesn't work anymore or at least only works on Windows.

Tagging all the traffic makes sense. A dedicated 3CX box really isn't going to have that much traffic outside of the VoIP traffic, and this covers everything (3CX tunneled traffic, WebRTC traffic, etc).

Glad you found a working solution.

 

[CedarglenHomes]

Tagging all the traffic makes sense. A dedicated 3CX box really isn't going to have that much traffic outside of the VoIP traffic, and this covers everything (3CX tunneled traffic, WebRTC traffic, etc).

Glad you found a working solution.

True, but I would rather not have my servers OS update traffic QOS tagged

 

[cobaltit]

Bah.... let your PBX get updates before everything else! But whatever works. I'm always in favor of the 'throw more bandwidth at it' approach.

 

[CedarglenHomes]

LOL