Intel PRO 1000 MT gigabit NIC on a FreeBSD 5.0 REL box. The box already has a separate NIC with a 192.168.1.x address. When bringing up a second interface on the same subnet as an existing interface, you have to tell which interface to use for broadcasts. The second interface can’t have the default netmask for the subnet. This was confirmed in this helpful post. To bring up the first (primary) interface: If you want to broadcast, use the second interface:”]
Source: https://taosecurity.blogspot.com/2003/07/im-testing-new-intel-pro-1000-mt.html