My PDC can’t PING my BDC HELP !!

My PDC and my BDC can’t PING between them. I
have NT 4.0 server on all my servers. I’m using IBM Netfinity servers. They have the same subnet 255.255.255.0 and they are under the same IP scope. 10.100.1.xxx

My BDC is also my Exchange Server 5.5

I have an LMhosts file running on both machines with the rigth IP addresses.