Alvarion VL , with Nat configured

Dear All,

I have this kind of problem on the routerboard in object with OS Lev.4

When I connect it only behind a Alvarion VL , with Nat configured on routerboard beetween two interface, upload stop work, and only download works done.
I tryed it behind 5 different VL and it’s always the same.

How can it be? Could be an eth problem ? I’ve used all kind of ethernet negotiation but no result and doesn’t seems an MTU problem.

Rgs

Max