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Within Firezone, there are multiple components that deal with DNS queries. Two of those components are the `l4-udp-dns-server` and `l4-tcp-dns-server`. Both of them are responsible for receiving DNS queries on layer 4, i.e. UDP or TCP. In other words, they do _not_ operate on an IP level (which would be layer 3) but instead use `UdpSocket` and `TcpListener` to receive queries and sent back responses. Right now, the interfaces of these crates are designed for the usecase of receiving forwarded DNS queries from the CLient on the Gateway's TUN device. This is a special-case of DNS resolution. When receiving a TXT or SRV query for a domain that is covered by a DNS resources, Firezone Client's will forward that query to the corresponding Gateway and resolve it in its network context. SRV and TXT records are commonly used for service discovery and as such, should be resolved in the network context of the service, i.e. the site that assigned to the resource. For that usecase, it made sense to allow each DNS server to listen on 1 IPv4 and 1 IPv6 address. Since then, our event-loop has evolved a bit, being able to handle multiple inputs at once. As such, we can simplify the API of these crates to only listen on a single address and instead create multiple instances of them inside `Io`. Depending on how the design of our DNS implementation for the Clients evolves, this may be used to listen on multiple IPs later (e.g. from the `127.0.0.0/8` subnet). Related: #8263
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.