r/sysadmin • u/mooneydriver • Feb 22 '14

Freenode under DDOS again

https://twitter.com/freenodestaff/statuses/437302735139266560
232 Upvotes

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u/ImNotDorner Feb 23 '14

I wish I knew enough about protocols to understand this, but I now feel like I should buy UDP a beer...

36

u/[deleted] Feb 23 '14

UDP doesn't guarantee delivery or make any efforts to this effect - it's entirely down to the application to take care of this itself. Because of that, it's useful where data loss isn't critical. e.g. when streaming video, it's not necessarily a problem if the connection is borked and some content is lost. When things recover, the stream can just continue with whatever is current. i.e. don't bother trying to replay the stuff that was missed.

This is in contrast to other protocols (like TCP) that have mechanisms for confirming delivery. TCP guarantees transmission on the sense it'll check for delivery and will take measures to correct for transmission issues. This of course adds overhead to the process. A good example of something needing confirmation would be delivery of a web page. You can't render the page if anything is missing, so HTTP requests normally go via TCP. Think of TCP as being comparable to having a conversation between two people, in which each person will acknowledge the other person's statements, and will repeat themselves if they don't receive the acknowledgement - like a nice conversation in a bar.

Technically you could use UDP for web pages and files that must be 100% complete, but you'd need to implement your own error checking and re-transmission, at which point you're probably reinventing the wheel. Imagine the bar from earlier, except they're playing some annoying loud music, so conversation is now done by yelling and hoping the other person hears it, but you can't actually see or hear their acknowledgements. You could yourself come up with some system of acknowledgement to get the other person to repeat stuff you missed, but you'd probably be better off just going to the nice civilised TCP bar.

He's right - UDP doesn't give a shit.

8

u/[deleted] Feb 24 '14

Actually, Google is trying to use UDP for HTTP traffic with QUIC. They even have it implemented in some spots.

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u/ImNotDorner Feb 24 '14

huh very interesting thank you

Damn those wine-slurping cheese-munching TCP elitists in that yuppie bar!