The MAC can access Internet in one building, but it can't from another building. 2 buildings have different IP, but only first building has Internet gateway.

Hi,

I did checked the proxy, there was nothing. I did ping the server in same IP range, it’s fault. But I can ping this MAC from a PC.

It found a strange IP ( which I didn't know where it came from) and stopped there.

1st building (which has Internet) IP 10.10.10.xxx, 2nd building IP 172.21.16.xxx. We use Bell fiber to link this 2 buildings. I ran command tracert on a PC in 2nd building, It found the gateway then 192.168.252.1 which is Bell link port, and backup to our gateway in first building. But on MAC it stopped at 192.168.252.1 afte ran the traceoute utility.

I don't think so as any PCs can access Internet from 2nd building, even I use my home laptop there. Also there is an older MAC works in 2nd building, and we want use a new one to replace that old one.