system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does the size of the packet impact the speed at which a firewall can process traffic?

Something that I do not entirely understand. Why is it that a router can have different throughput ratings depending on the size of the packets?

If a router receives a 1518 byte and can achieve 100 mbps. Yet the same router receives a 64 byte packet and the throughput drops to 50 mbps for example.

Why is that?

Since the router can handle large packets wouldn't the small ones just glide right through?
gpt
Since the firewall has "packet inspection" it needs to stop, open, analyze, close and pass along each packet.  So....if you have larger packets there is simply less of the "stop, open, close and pass along" parts of that process.  The analyze takes a smidge longer, but the elimination of all the per-packet overhead improves the overall performance.