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:

(Almost-)Zero-Additional-Latency UDP-over-TCP

Quote: “we realize that for some of the Clients – UDP just doesn’t work because of some weird firewall between Client and Server”
Another Quote: “there is nothing to block us (so head-of-line blocking doesn’t apply)”
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TCP Peculiarities as Applied to Games, Part II

Quote: “Nagle’s algorithm aims to deal with those [CENSORED] developers who’re trying to send data over TCP in really small chunks (like 1 byte each time)”
Another Quote: “it seems that “proportional rate reduction” (PRR, reportedly used by Linux kernels by default starting from 3.2) performs for gaming purposes a little bit better than the alternatives”
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TCP Peculiarities for Games, part 1

Quote: “the best we can hope when using a single TCP connection over 5%-loss channel – is having 1.5-second “lag spike” every 5 or so minutes, and a 3-second “lag spike” every 2 hours.”
Another Quote: “we may already have the-information-we-need on the receiving host – but this information is hidden from us by layers of abstraction on receiving side”
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Packet Loss for an App-Level Developer. Part II. Last Mile, Wi-Fi, and Summary

Quote: “Burstable packet loss. May be caused by a neighbor preparing his breakfast”
Another Quote: “if there is a NAT device on the way from your Client to your Server – a sudden IP change can occur with absolutely no notification to Client whatsoever.”
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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.”
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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”
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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”
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