[thomseddon]

Both are valid addresses and can be assigned to hosts.

Network address is only really used for directly attached networks, non directly attached networks will route to any address in the block correctly.

Same for broadcast address, they're also relative to whatever block you're talking about at the time, so whilst 3.255.255.255 is the broadcast for 3.0.0.0/8 subnet it's just another "usable" address in the 3.0.0.0/5 subnet and when you send a packet then you, and probably your router, don't know what subnets in use on the other side :) (unless it's directly attached)