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Comment by mrpelz | Hacker News Reader

Keep in mind that the way the second Ethernet interface is connected to the Pi will have an impact on performance.

The board mentioned above uses PCIe, as does the even smaller alternative “Raspberry Pi Compute Module 4 IoT Router Carrier Board Mini” from DFRobot [1].

Other boards use USB 3, like the “Dual Gigabit Ethernet NICs Carrier Board for Raspberry Pi Compute Module 4” from SeedStudio [2].

I wouldn’t recommend using USB.

[1]: https://www.dfrobot.com/product-2242.html

[2]: https://www.seeedstudio.com/Rapberry-Pi-CM4-Dual-GbE-Carrier...

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>I wouldn’t recommend using USB.

I've heard this from networking wizards all the time during my internship but nobody actually explained whats wrong with usb to ethernet NICs

As the unfortunate owner of an intel NIC, USB ones where actually way more reliable.

USB NIC consumes more CPU. Also if you are trying to use pfSense or another *BSD based router, they don't support the USB NICs very well. I ran that setup for a bit and it was dropping packets left and right. After I switched to a Linux kernel all the issues disappeared. The problems are mostly software, not hardware.

Also, if you use a hypervisor and your router in a VM with USB pass through. The overhead on the CPU for USB pass through is significant. Better to PCI pass through the entire USB controller.

So, there are gotchas and pit falls but they are mostly manageable and avoidable with a bit of understanding.

I ran a pi4 + USB NIC as a router for years before switching to proxmox VM based router (still USB NICs). It was fine, the switch was rough until I figured out the issues.

I had similar experience. Passing a USB2 NIC to pfSense in VM. The performance was horrible.

What gave USB NICs a bad reputation in the SBC community is that before the RPi4 the USB bus was USB 2.0 (the RPi4 has a USB 3.0 bus) and this meant that the max speed was 480 MBps if the NIC consumed the entirety of the bus. A USB NIC would never be able to get to 1 Gbps speed no matter what might have been claimed.

With the RPi4 you have USB 3.0 on the main USB bus so the max bandwidth there is now 5 Gbps, but the next bottleneck to be faced is the PCIe x1 bus that is used to connect these CM4 modules to the third-party carrier boards. Now you are hitting a 4 Gbps limit.

> As the unfortunate owner of an intel NIC

Odd comment. Intel are one of the best NIC vendors out there.

What was your specific device and problem?

https://wccftech.com/intel-foxville-i225-v-2-5gbe-networking...

Hosting specific things (minecraft and smb in my case) has a chance of crashing it so hard only a power cycle fixes it.

It's hard to reproduce with smb but with MC I can reliably make it crash by spawning a couple hundred mobs in quick succession.

At least there's an easy workaround - just use 1Gbps mode.

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