> 'unique' is a very mild expression. The word you're actually looking for was probably 'wrong'. > > Your gateway *must* be in the network your interfaces are in. You also would not want your living room be built without any doors and a sign on the wall 'the exit is in the kitchen'. There does exist one use case that was pointed out on IRC that might be valid ... although the OP is somewhat abstract in his original definition so this might not apply... In the event an ISP provides new IPs and routes them to your host but these are outside of the pre-existing subnet it is possible to use them with no gateway in the subnet associated with these (it's essentially a point to point link directing traffic at an interface)... This somewhat describes the situation: http://www.adminsehow.com/2011/09/gateway-on-a-different-subnet-on-linux/ However it is a rather specific use case and may not apply here...