I've been following the issue CM4 is missing IEEE1588-2008 support through BCM54210PE since I heard about IEEE1588-2008 support on the Compute Module 4 last year.
Apparently the little NIC included on every Compute Module 4—the BCM54210PE, which is different than the NIC on the Pi 4 model B (a BCM54213PE)—includes support for a feature called PTP, or Precision Time Protocol.
As I start using Raspberry Pis for more and more network routing activities—especially as the Compute Module 4 routers based on Debian, OpenWRT, and VyOS have started appearing—I've been struggling with one particular problem: how can I set routing priorities for network interfaces?
Now, this is a bit of a loaded question. You could dive right into routing tables and start adding and deleting routes from the kernel. You could mess with subnets, modify firewalls, and futz with iptables.
But in my case, my need was simple: I wanted to test the speed of a specific interface, either from one computer to another, or over the Internet (e.g. via speedtest-cli).
The problem is, even if you try limiting an application to a specific IP address (each network interface has its own), the Linux kernel will choose whatever network route it deems the best.
Since the Raspberry Pi Compute Module 4 was introduced last year, I've been testing a variety of PCI Express NICs with it. One of the main types of NIC I'm interested in is cheap 2.5 Gigabit Ethernet adapters.
2.5 Gigabits is about the highest reasonable bandwidth you can get through the PCI Express Gen 2.0 x1 lane on the Raspberry Pi, and it's also a lot more accessible than 10 Gigabit networking, especially for home users who might already have Cat5e runs that they are loathe to swap out for Cat6 or better cabling.
In my testing, besides discovering that not all 10 Gbps SFP+ transceivers are created equal, I found out that when it comes to performance, the Linux driver you're using matters—a lot.
There could be a thousand reasons something like this happens, but here's my situation:
A few months ago, when I was testing 10 Gigabit networking on the Raspberry Pi, I noticed something funny when I was doing iperf3 speed tests between devices connected through my MikroTik CRS305 10G switch.