DSCP settings for Zoom on a Cisco AutoQoS enabled network

[myxxymoxx]

Hello,

I have a question about AutoQoS on a Cisco LAN. The LAN is all enabled by using AutoQoS and the Access Switches are configured to trust Cisco IP Phone. Now if I was to pull that phone out and connect the LAN directly to a PC which is using a Zoom client I don't think the QoS will be trusted as by default marking values are 56 (CS7) for audio, 40 (CS5) for video, and 40 (CS5) for screen sharing. I believe Cisco is trusting the following (is this right?)

• Voice with a dscp 46 or EF,
• Interactive video 34 or AF41,
• Streaming video as dscp 32 or CS4

So, if I was to change the DSP settings on the Zoom client, the LAN will trust these IP Packets and queue them accordingly?

[Roger Kallberg]

No. As the trust is also looking for if the traffic originated from a Cisco phone, with the use of CDP information, it would not trust the traffic that originates from the PC. You’d need to implicitly trust the traffic on the port to honour the DSCP value received or create another match criteria for this, for example use a ACL to map out what traffic to trust. There are plenty of reading material on this available if you search for it with your favourite search engine.

[Mohammed al Baqari]

Hi,

I am not sure what version of AutoQos you are using, but the concept of
trust and untrust using CDP has been deprecated by Cisco. QoS SRND (AutoQos
4.0) uses a combination of ACLs and DSCP marking with match-all classes to
match interesting traffic. This is needed to match SoftClients such as
Jabber, Teams, Zoom, etc).

So you need to start configuring class-maps to match ACLs along with DSCP
markings from the clients to trust traffic and set the right CIR/MIRs.

Also, keep in mind that Windows by default reset all DSCP markings. Hence
you need to install Zoom as administrator or use GPOs to set DSCP markings
for zoom and untrust other applications (I suggest the GPO approach
because it is more unified).

The approach I suggest is to enable auto-qos, get the syntax of applied
config, then start editing it to match your applications DSCPs and IP.
Finally, remove auto-qos and apply your script.

Here are some references.

https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst9500/software/release/16-6/configuration_guide/qos/b_166_qos_9500_cg/b_166_qos_9500_cg_chapter_00.html
https://support.zoom.us/hc/en-us/articles/207368756-Using-QoS-DSCP-Marking

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