6 ms·

> the extras UDP provides Like what? UDP is lightweight and bare-bones, no?

• ncmncm 7y ago
  It adds source and destination ports and a checksum. Computing the checksum is a nuisance, and it is usually inadequate, so it is allowed to be zero in IPV4, but not IPV6. Normally, if you need a checksum, you need one that cannot be forged, and you need more than 16 bits. So the L3 one is just overhead. I have never seen an actual use of UDP that looked at the port numbers, although firewalls often use them for filtering.
  • detaro 7y ago
    Name a few UDP-based protocols whose implementations do not listen to only a specific port number, or a rely on port numbers established as part of the protocol flow, then?
    • sk5t 7y ago
      This is a weird thread. I too would be interested to know about these uses of UDP that don't use ports to post data to processes (or even traverse NAT I guess?).
      • ncmncm 7y ago
        Yes, I was completely wrong. PBKAC.
  • MaxBarraclough 7y ago
    > Computing the checksum is a nuisance, and it is usually inadequate, so it is allowed to be zero in IPV4, but not IPV6. If IPv6 disallows simpy zeroing the field, that sounds like it's not just a nuisance. > I have never seen an actual use of UDP that looked at the port numbers, although firewalls often use them for filtering. I don't know what you're saying here. UDP's ports model isn't optional in any sense, it's just like TCP's. If you run several UDP-based services on your server, port numbers are how the server knows which packets are destined for which processes.
    • ncmncm 7y ago
      OK. Too much time spent in kernel-bypass coding. But the checksum is very anemic, inadequate when correctness matters.