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For DNS resources, the Gateway maintains a per-peer NAT table from the client-assigned proxy IPs to the real IPs of the domain. Whenever the Client re-queries a DNS resource domain locally, we asynchronously ping the Gateway to also re-query said domain. This allows us to detect changes in the DNS records of DNS resources. To avoid breaking existing connections, the mapping between proxy IPs and real IPs is currently not updated if there are any active UDP or TCP flows for a proxy IP. This logic turns out to be unnecessarily restrictive as TCP flows can linger around for up to 2h before they timeout if they are not closed with a TCP RST. What we really need to do is always update the mapping of proxy IP <> real IP but honor existing NAT table entries when we route packets before creating new ones. This ensures that an existing connection to a previously resolved IP remains intact, even if a later DNS response for the same domain updates the mapping. At the same time, new connections (i.e. with a different source port) will immediately use the new destination IP.
Connlib
Firezone's connectivity library shared by all clients.
Building Connlib
You shouldn't need to build connlib directly; it's typically built as a dependency of one of the other Firezone components. See READMEs in those directories for relevant instructions.