how to stop if from using route with mac address as gateway



i have two servers which their ips are on the same subnet and they have the same default gateway. the one is with linux and the other with a mac osx

we received a mail from the datacenter saying that for that kind of servers that communicate with each other we have to add a static ip like that because they're changing their network infrstracture:

for linux server for example
destination: mac_ip gateway: default_gateway_ip

I set those static IPs but the servers still cannot communicate

I see that mac server instead using the route i added is using the one below:
linux_ip 54:75:d0: UHLWI 14 85663 en0 709

it's using the route with mac address. how can i stopped that?
i deleted the arp entry for linux server but still the same.

What do you suggest?

mac version:
ProductName: Mac OS X
ProductVersion: 10.6.8
BuildVersion: 10K549

on linux server since i added the static route the arp entry for mac was gone.
what do you suggest?
i do understand how tcp/ip and direct connections on the same subnet works - on network layer - but as i told you there's no direct connection any more but it's just trying to reach it as it is. this arp entry is on status incomplete and though i delete it it keeps coming. Even after a restart. I do believe now that it's because of the network implementation so i asked the datacenter support to have a look. on the linux server when i entered the static route the incomplete arp entry was gone from the arp table. i access the server via terminal. thank you for responding.
Now is this Linux Server support an Open directory or an Active directory? This Linux servers sounds like the Mail Domain Server? Am I correct?

Does the pop go from the modem directly to this Linux server?
no there's no open or active directories. The problem was fixed from the datacenter, probably they had done something wrong on network implementation after the changes they've done on their network topology.

thank you very much for your help.