Re^4: udp send not reporting host unreachable errors

How do you propose this is done? Making the actual send() wait for a possible ICMP package is not practical, as you do not know whether there will come one, and you will not get a success message if the package was accepted.

It is not practical. I am not going to use it. My pursuit is not to know whether the code snippet I wrote is practical, it is - why isn't the application behaving as I think it should? My point is: I should be getting 'Destination Unreachable' errors like I got for 'Connection Refused'.

Comment on Re^4: udp send not reporting host unreachable errors

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Re^5: udp send not reporting host unreachable errors
by roboticus (Chancellor) on May 05, 2009 at 16:32 UTC

saurabh.hirani

You don't understand: You'll receive an error only if the machine sends you an error packet which makes it all the way back to your machine. The 'Connection Refused' is a message from the destination machine¹ telling you to go away. No machine means there's nothing to receive the packet and send you an error result.

Why can't some other computer send you a 'Destination Unreachable' message? Well:

Whose responsibility is it to do that? No one has that responsibility.
How can they tell that the host doesn't exist? Since a computer doesn't have to support any network services, there's no way for a different computer on the network to tell if the computer actually exists or not.

If you require feedback, then you need to use a connection with TCP.

...roboticus

1. Usually it's the computer. Some firewalls, however, can be configured to send a 'Connection Refused' because the network administrator doesn't want that sort of inbound packet.

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