a ton of routers (think, high end access or core platforms) use "unroutable" ip space for internal communication between different systems in the router. These

a ton of routers (think, high end access or core platforms) use "unroutable" ip space for internal communication between different systems in the router. These are hardcoded addresses used in the backplane of the system, and changing them would be incredibly difficult because usually: - these routers have multiple forwarding and control plane systems for redundancy purposes, and upgrading them all at the same time is usually not feasible. (remember, these system are build redundantly because you want no downtime on a core router). - Some of these prefixes are used for constructs inside the routers (virtual interfaces between forwarding planes for instance). This might be called ugly, but it is the way it is. and changing that is near impossible.