Cannot reach MBL IP from MAC

I have OSX 10.6.which is connected wiressly to my router. MBL is connected to DLINK switch and then to router switch ports.

After some time MBL become unreachable from MAC by ip and domain name. But it’s reachable from other devices conected wirelesly and by patch-cords. tcpdump on MBL shows that MBL receives ICMP packets and send’s replies, but for some reason tcpdump on osx doesn’t see them.

Next day MBL become reachable again, but after some time when copyint big file from MAC to MBL it again became unreachable from MAC with the same sympthoms.

Thanks in advance for your help

Try mapping the drive