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I know that UDP has no real error control facilties outside of silent discard of packets failing checksums.

Am I correct in thinking that a UDP packet with a TTL=1 reaching a router will generate an ICMP Time Exceeded message, and a UDP packet arriving with an unused port # (54823 or something) at an end host will be rejected, causing an ICMP Port Unreachable message - and that both of those ICMP messages would be sent back to the originator of the message?

I'm pretty sure that's how it works, but I wanted to make sure I wasn't confusing myself somehow

John Humphreys
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Yes, you're right. That is also how traceroute does it.

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That's right, but if you want to receive those messages in your app you have to use connect for the socket.

Karoly Horvath
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