Re: connect(2) for UDP

 
> I got the idea from Chapter 8.11 of Stevens's "Unix Network Programming",
> Volume 1, 3rd edition, page 252.  And he says what you said:
>
>	"[T]he kernel just checks for any immediate errors ... records the IP
> address and port number of the peer ... and returns immediately to the
> calling process."

Yep.  For UDP, having the other end not be listening is not an immediate error.

> The same program, when trying to communicate with a down host, times out
> reading.  Not surprising, on reflection, because there's no machine to
> send that ICMP message.

Note that some last-hop routers will make an ICMP Host Unreachable response
on a down host, because the ARP fails.  I don't know if this will be turned
into a useful diagnostic by the UDP layer.  In any case, it takes some time
for it to decide if the ARP has timed out.

Craig