Poor Performance with ZCC on MacOS BigSur


We’re actual running a PoC with Zscaler and we are confronted with some strange performance issues with ZCC on MacOS. The support seems a little bit clueless so I want to ask if someone facing the same issues or has an idea what could be wrong.

We’re using the following configuration:

  • MacOS Big Sur and Catalina, lastet Patch level, only Intel CPU
  • Tunnel Version 2.0
  • ZCC version and (beta)
  • PAC File routes traffic only through german datacentres Frankfurt and Munich
  • WAN connection tested via fibre (Deutsche Telekom 300Mb/sec syncron) and different coaxial cable connections in homeoffices (Vodafone up to 600 Mbit /sec down and 40 Mbit /sec upstream)
  • same Forwarding Profile for all Clients

If we do some speed tests via fast.com, gateway.zscaler.net/test or simply download some testing files via “Speedtest Belwü” we facing a speed degradation with activated ZCC to more then a half of the regular speed without Zscaler.
At the homeoffice from one colleague the speed drops vom 240 to 65-70 downstream.
Tested with several devices and WAN connections.

With windows clients there are no speed issues, sure a little bit degraded performance because routing through Zscaler network but not this huge impact at all.

We disabled and uninstalled Endpoint Security, disabled the MacOS Firewall and tested with devices complete separated from MDM policies. We also thought that it has something to do with carrier grade NAT at Vodafone WAN connections, but the issue persists also on our fibre connection which is only using IPv4.

The whole issue is only mostly observable by WAN connection with more than ca. 150MBit /sec downstream. With less the full bandwidth is used.

I’m happy for any suggestions or ideas.

Solution found here
Kudos to @snafu and @manuel

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