Ports doubt, check network performance...?

[perikillo]

   Hi people.

    I have some problems on my network, and i want to use my freebsd
box to see if i can find the problems on my network, we have two
networks in two countrys connected by a private link, but i have seen
just a couple a weeks ago that we have some problems between both
links, we are lossing packets if i ping some server on the other link,
some times i get 36% of packets loss, is to but to much on bussines
hours.

    I want to use my freebsd box running 6.0 but just want to know if
some one could recomend me wich ports to check to see if i can find
wich device is causing this problem.

   Thanks any help will be apreciated, greetings!!!