For pass-by monitoring and filtering, you need to setup a mirroring port in your switch. When port mirroring feature is enabled, the switch will replicate data from other ports onto a single port for monitoring purpose. Since the original packets will not be hold or delayed, port mirroring does not affect your network speed theoretically.

However, inproper port mirroring settings will cause heavy load in your switch and even cause packet loss.

So please consider the following points when configuring a mirroring port:

1. Do not mirror multiple ports to one port until necessary.
2. If it is required to mirror multiple ports, please make sure the total mirrored ports throughput will not exceeds the mirroring port throughput limit.
3. For WFilter, mirroring the internet port is enough. Usually, only the router/firewall port needs to be mirrored.
4. If your switch does not allow outgoing traffic on the mirroring port, or you’re using WFilter to filter internet access for more than 50 computers, it is recommended to use two network adapters: one is for monitoring only, another one is for filtering.

How to check whether port mirroring settings are correct?
How to check whether a switch supports port mirroring?
Why a port mirroring switch is required to monitor my network?