11/14/2022 0 Comments Reasons for socker error 1To illustrate this, let's write an UDP echo server. Traditionally on the server side UDP requires unconnected sockets. It can be done with connect(AF_UNSPEC), but this is rather advanced Linux magic. Depending on the specifics of the setup this might save some CPU cycles.įor completeness, it is possible to roll a new source port and reuse a socket descriptor with an obscure trick called "dissolving of the socket association". Generally speaking for outbound traffic it's preferable to use connected UDP sockets.Ĭonnected sockets can save route lookup on each packet by employing a clever optimization - Linux can save a route lookup result on a connection struct. For security, DNS assumes the client source port is unpredictable and short-lived. It is tempting to reuse the socket descriptor and query another DNS server afterwards, but this would be a bad idea, particularly when dealing with DNS. Otherwise, the program can get confused by some random inbound internet junk - like port scanning. Which one is better? In the second case, when receiving, the programmer should verify the source IP of the packet. First snippet is using a connected socket: They do the same thing - send a packet to the DNS resolver. To illustrate the latter, consider these two snippets. It is possible to use connected sockets for ingress handling, and unconnected for egress. UDP clientĪs we'll learn today, these can be mixed. Traditionally the connected sockets were mostly used for outgoing flows, while unconnected for inbound "server" side connections. Connected sockets have a full 4-tuple associated. UDP sockets can be "connected" (or "established") or "unconnected". How do you "accept" connections on a UDP server? If you are using unconnected sockets, you generally don't.īut let's start with the basics. In this blog post we'll cover the basics: all you need to know about UDP servers to get started. We have a lot of generic UDP traffic going through our Spectrum service.Īlthough UDP is simple in principle, there is a lot of domain knowledge needed to run things at scale. We operate WARP - our Wireguard protocol based tunneling service - which uses UDP under the hood. QUIC is a new transport protocol based on UDP, it powers HTTP/3. Stateful UDP gains popularity for a number of reasons: Recently though, we started operating big scale stateful UDP services. We've spent significant effort optimizing traditional HTTP/1.1 and HTTP/2 servers running on top of TCP. Historically Cloudflare's core competency was operating an HTTP reverse proxy. Snippet from internal presentation about UDP inner workings in Spectrum.
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