Device interrupts will feed the generator so that the output from the CSPRNG is indistinguishable from random. There's lots of stuff happening on a network tha

Device interrupts will feed the generator so that the output from the CSPRNG is indistinguishable from random. There's lots of stuff happening on a network that's impossible to guess and replay. This is also called noise. Keep in mind that the CSPRNG generator only needs a random seed, then it can produce psuedo random numbers all day long. Linux will continue to reseed as more interrupts occur. Linux will also save a 512 byte file on shutdown and seed the generator with it on the next boot up, so you immediately enter into a safe/random state.