If you're in trouble and cannot find an answer to a question which goes beyond Stack Overflow...
If you have a not-so-usual solution for your problems but need to justify it to your boss...
If you like to think on your own rather than blindly follow "common wisdom" and "profound truth"...
...then 'No Bugs' Hare on Soft.ware might be the right place for you.
Your mileage may vary. Batteries not included

Network programming is one field which everybody uses but very few people really know in depth. Our IT Hare did write a software which processes billions of network packets per day; moreover, they’ve done it in a very robust and efficient manner. And last but not least, they’re ready to share their experience :-)

Network Programming, page 1:

Packet Loss for an App-Level Developer. Part I. Router Failures, BGP Convergence Time, AQM, Traffic Shapers.

Quote: “All the routers, switches (actually – pretty much each and every device which forms Internet infrastructure) – are allowed to drop each and every packet.”
Another Quote: “TCP, when it observes a dropped packet, interprets it as an indication of congestion – and slows down.”

War on Clones, Part I. IP-based (non-)Identification. Identifying PCs and Macs

Quote: “NEVER EVER use IPv4 for long-term bans”
Another Quote: “If using MAC addresses to identify devices, you SHOULD gather stats on repeating MAC addresses within your DB”

Marshalling and Encodings

Quote: “Encoded data size is especially important for Client-Server communications, and less important (within reason) for Server-to-Server ones and for locally-stored format.”
Another Quote: “On the other hand, due to being optimized for CPU operation, Flatbuffers are NOT optimized space-wise; even compared to not-so-optimal-space-wise Google Protocol Buffers, Flatbuffers can lose additional 1.5x in size”

Network Programming: Socket Peculiarities, Threads, and Testing

Quote: “I am not saying that this architecture is the only viable one, but it does work for TCP for sure (and performs reasonably well too)”
Another Quote: “The whole task of optimizing performance beyond, say, 20-50K packets/second per box tends to be Quite Elaborated, and involves quite a few things which are platform- and hardware-dependent.”

UDP for games – security (encryption and DDoS protection)

Quote: “Yes, you DO need to encrypt your UDP traffic. And no, using UDP is NOT a valid excuse to skip encryption”
Another Quote: “Personally, I prefer to think of it as of insurance – when I’m paying my premiums in hope that my money will go to waste.”

UDP from MOG Perspective

Quote: “you may think of UDP as of an analog of good old C: you can do pretty much everything, but it is not because the language helps you – it is rather because it doesn’t stand in the way :-)”
Another Quote: “As most of the routers (including pretty much every backbone router out there) are not configured to support multicast, it makes multicast over the public Internet hopeless :-(“