hardware loopback test with plug

[bruno schwander]

Hi,

I am trying to configure FBSD 4.8 to do an ethernet loopback test. I want
to be able to sent packets over the ethernet interface, and a device
hooked up to the ethernet port (at the very minimum, an RJ-45 loopback
plug, i.e.  with pins 1 & 3 and 2 & 6 connected together)

This is to test a type of network transmitter. There exist a description
of a test setup done using Linux here
http://ronja.twibright.com/tetrapolis/testing.php, but applying the same
principles does not seem to work on FBSD.

Essentially, I would like to be able to ping the interface, and if the
loopback plug is hooked up, then tcpdump should show the packets received,
otherwise, nothing should be seen.

Anybody knows how to do that ?

I have been manipulationg arp tables and routes to no end, I do not see
how to make this work.

Any help appreciated

bruno