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Nobody's claiming TCP/IP to be based on UDP/IP. I mean to suggest that buffering isn't a proper feature distinction between TCP and unreliable protocols. Sepa

by sk5t 7y ago

Nobody's claiming TCP/IP to be based on UDP/IP. I mean to suggest that buffering isn't a proper feature distinction between TCP and unreliable protocols. Separately, it seems a tad obscure to use IP as the exemplar here--doesn't most everyone want UDP features on top?

ncmncm 7y ago
Hardly anybody relies on any of the extras UDP provides, so they are typically just wasted overhead. But user-level libraries offer UDP, so that is what people use.
- kragen 7y ago
  I've never seen a UDP application that didn't depend on port numbers, which are an extra UDP provides.
- MaxBarraclough 7y ago
  > 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.

by sk5t 7y ago

ncmncm 7y ago

Hardly anybody relies on any of the extras UDP provides, so they are typically just wasted overhead. But user-level libraries offer UDP, so that is what people use.

kragen 7y ago
I've never seen a UDP application that didn't depend on port numbers, which are an extra UDP provides.
MaxBarraclough 7y ago
> 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.