USG FLEX 200H: Shared BWM still affects unrelated VLANs on current firmware

This appears to be the same Shared BWM issue reported in this thread in April 2025.

https://community.zyxel.com/en/discussion/29056/usg-200h-wan-upload-problem#latest

Since that discussion is now closed, I am opening a new thread because I can still reproduce the issue on the current USG FLEX 200H firmware.

My setup:

• USG FLEX 200H
• Latest available firmware V1.39(ABWV.0)
• 1 Gbit/s symmetric WAN connection
• Multiple VLANs
• BWM configured locally on the firewall
• Several Shared BWM rules, each intended to limit only one specific VLAN

One example is a Shared BWM rule with:

• Incoming interface: VLAN 172
• Source: full subnet of VLAN 172
• Outgoing interface: WAN
• Destination: any
• Service: any
• Upload limit: 80 Mbit/s, just for testing

The problem is that this limit also affects traffic that should not match the rule.

I tested this directly from a dedicated configuration port (p8) on the firewall. This port is not part of VLAN 172 and is not subject to any intended bandwidth restriction.

I also repeated the test on several different WLANs assigned to different VLANs. All of them show the same behavior: as soon as BWM is globally enabled, the upload speed is limited to roughly the value configured in one of the Shared BWM rules, even though the corresponding rule is disabled and the traffic originates from a different VLAN.

Results:

• BWM globally disabled: about 700 Mbit/s upload
• BWM globally enabled, but all custom BWM rules disabled: about 80 to 90 Mbit/s upload
• The same behavior occurs on several different WLANs and VLANs
• The measured value corresponds closely to the 80 Mbit/s upload limit configured in one of the disabled Shared BWM rules

All custom BWM rules are shown as disabled in the local GUI. The default BWM rule has no bandwidth limit configured.

This shows the relevant interfaces and confirms that the test client is connected through a separate configuration port p8 and not through the VLAN affected by the BWM rule.

This looks very similar to the behavior already described earlier in this thread, where a Shared BWM rule for one VLAN also affected traffic from another VLAN, and disabling the rule did not fully remove the bandwidth restriction.

In my case, disabling BWM globally immediately restores the expected upload speed.

I found another important detail while testing:

The order or priority of the BWM rules themselves does not seem to have any effect. Instead, the upload traffic is always shaped according to the values configured in the rule with the lowest Traffic Shaping priority, regardless of whether that rule should actually match the tested interface or VLAN.

I also confirmed that this behavior only affects the upload direction. Download traffic is not affected in the same way.

Can Zyxel confirm:

1. This issue was reported in this thread almost 1.5 years ago and I can still reproduce essentially the same behavior on the current firmware. Has Zyxel still not fixed this, or is this now considered a known limitation of Shared BWM on the USG FLEX H series?
2. Since Per-Source-IP limits each client individually, it does not solve my use case. I need one shared bandwidth limit for the entire VLAN. Is there currently any reliable workaround or supported method to achieve this on the USG FLEX 200H?

For me, reliable and predictable bandwidth management is a basic requirement for this type of firewall. If Shared BWM cannot reliably limit one VLAN without affecting unrelated traffic, Zyxel is no longer a viable option for future deployments.