Date: Wed, 10 Dec 2025 15:25:21 +0100 From: Peter Eriksson <pen@lysator.liu.se> To: "net@freebsd.org" <net@FreeBSD.org> Subject: Is it possible to force packets to go over a loopback cable? Message-ID: <3C76FF27-49A7-4C45-8E8F-51C1BBF3C6E0@lysator.liu.se>
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I’d like to find some way to force FreeBSD to send a stream of packet over a loopback cable connected between two ethernet ports on the same machine, but it seems FreeBSD also short-circuits it and handles that traffic internally in the OS. Which normally is a good thing for speed, but bad when you are trying to test suspect cables :-) I’ve found references that back in the pre-FreeBSD 10 days there used to exist a sysctl: net.link.ether.inet.useloopback that could be set to 0 to disable this internal shortcut and force the packets out onto the cable… Any suggestions? :-) - Peterhelp
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