Here’s a chunk from the new Networking for System Administrators.
Here’s the catch. The listed speed is not how fast the interface can pass traffic. Think of the speed as a language. Your server’s NIC might speak and understand the 2.5G protocol, but that’s no guarantee that the server, card, or network can support passing that much traffic. Actual throughput depends on how the NIC is attached to the host’s bus, the network cable, the load on the switch, and more. Some low-quality NICs speak the protocols but are built on hardware incapable of passing a tenth of the claimed bandwidth. Servers that can’t push 2.5G might ship with 10G interfaces. Some NICs speak the 10G protocol but interrupt so frequently they can’t even reach a gigabit. Certain vendors run benchmarks using carefully crafted packets so they can claim performance you will never achieve in reality.
This isn’t new; gigabit Ethernet first appeared on hardware incapable of handling even a hundred megabit, just so that vendors could advertise the new feature.
I keep having to circle back to the beginning of this book to fix boneheaded errors. The first edition doesn’t even mention virtual interfaces! I’d appreciate your support in getting this done.