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DNS resolution is a shared resource. The DNS client is typically a user-space OS service that resolves and caches DNS requests. What is resolved by one application is cached and reused by another. But at the app level, there are is no deconflicting happening like transport layer protocols. However, the same can be said about IP, IP addresses like name servers are configured system wide and shared by all apps.

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It can be shared access to a cache, but this is an implementation detail for performance reasons. There is no problem with having different processes resolve DNS with different code. There is a problem if two processes want to control the same IP address, or manage the same TCP port.

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Yeah, but there is still no reason why an "ip_stack" process can't ensure a different IP isn't used and a "gnu_tcp" or whatever process can't ensure tcp ports are assigned to only one calling process. An exclusive lock on the raw layer 2 device is what you're looking for I think. I mean right now, applications can just open a raw socket and use a conflicting tcp port. I've done to kill TCP connections matching some criteria by sending the remote end an RST pretending to be the real process (legit use case). Which approach is more performant, secure, and resilient? that's the what i'm asking here.