You mention communication protocols. There was a recent article here about a tool bridging an ipv6 only Linux box to the ipv4 world using LD_PRELOAD. A kernel

You mention communication protocols. There was a recent article here about a tool bridging an ipv6 only Linux box to the ipv4 world using LD_PRELOAD. A kernel module could trap the calls in a more clean way. https://news.ycombinator.com/item?id=35773554 https://news.ycombinator.com/item?id=35773554