UDP Traceroute on FreeBSD

Michael Sierchio kudzu at tenebras.com
Mon Oct 3 15:35:14 UTC 2016

On Mon, Oct 3, 2016 at 5:52 AM, Mark Tinka <mark.tinka at seacom.mu> wrote:

> Can anyone tell me whether FreeBSD is able to respond to traceroute
> packets transported over UDP?

Absolutely, yes - unless firewall rules drop stray UDP packets inbound, or
the kernel parameter net.inet.udp.blackhole is set to 1.

Also note that traceroute only yields the expected behavior (an ICMP
PORT_UNREACHABLE which terminates the trace) if nothing is listening on the
selected port on the IP address you're tracerouting to.

"Well," Brahma said, "even after ten thousand explanations, a fool is no
wiser, but an intelligent man requires only two thousand five hundred."

- The Mahābhārata

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