what size of the buffer is sufficient for UDP case of recvfrom?

Question

I'm using recvfrom to receive udp multicast data. As far as I know it receives not more than 1 datagram in call (is that correct?). What buffer size would be enough for such call then? I guess it should be ~MTU of UDP for this machine, but how can I know it on runtime?

I don't want to "overestimate" size of the buffer because I actually have ring-buffers of buffers under the scene and I don't want to spent too much extra memory.

Answer 1

The maximum size of an UDP datagram is 64k. Unless you're allocating a lot of buffers, just use this size.

Answer 2

The maximum size of an IPv4 UDP datagram payload is 65507 bytes, but you won't be getting them other than via the loopback. The best you can do across a real network is the MTU minus 28. The generally accepted practical limit without fragmentation is 534 bytes.