Julia EvansJun 19, 2024

when I asked people to explain how UDP works I got a lot of answers to the effect of "it's spray and pray"

but I'm having trouble thinking of examples of UDP-based protocols that actually work in a "spray and pray" way —

* DNS is "send 1 packet, retry if you don't get a reply”
* QUIC is a sophisticated system for streaming data over UDP
* I'd guess that video protocols correct for packet loss
* maybe statsd is a "spray and pray” system?

(please do not reply to this explaining how UDP works)

Show threadStéphane Bortzmeyer

@b0rk DNS NOTIFY? You send the packet but never expect any form of ack.

There are may be other types of best-effort notification working the same way.

Jun 19, 2024 at 1:35pmWeb
Show threadCsillag TamásJun 19, 2024

@bortzmeyer @b0rk
There is a response defined in RFC1996 4.7:

"It will also send a NOTIFY response back to the NOTIFY request's source, with the following characteristics..."

https://datatracker.ietf.org/doc/html/rfc1996

RFC 1996: A Mechanism for Prompt Notification of Zone Changes (DNS NOTIFY)

This memo describes the NOTIFY opcode for DNS, by which a master server advises a set of slave servers that the master's data has been changed and that a query should be initiated to discover the new data. [STANDARDS-TRACK]

IETF Datatracker
Show threadJohn W. O'BrienJun 19, 2024
@bortzmeyer @b0rk This seems like a good example of an optimization where successful delivery of the NOTIFY will promote rapid replication of zone changes, but the value of doing so and the consequences of failing to do so are small. The reliability and corresponding costs of TCP is not justified.