- Local vs. remote: If a host is on the same subnet, it can be reached via L2. If the host is on a different subnet, traffic must leave the subnet via a default gateway (i.e., router or L3 switch).

- In a routing domain, network addresses are unique. Firewalls, transport and application load balancers and some security gateways break this rule, but also create separate domains.

- Routers do not maintain state. This is not true when using Multiprotocol Label Switching (MPLS) or Resource Reservation Protocol to reserve bandwidth, typically for voice or video over IP. Nevertheless, general network layer route discovery is used to find the paths over which bandwidth can be reserved.

The local vs. remote problem, and finding the local gateway

Remember the local vs. remote assumption on LANs, which does not always hold on hub-and-spoke media such as Frame Relay. When you provide redundant first-hop gateways (i.e., routers or L3 switches), the local hosts need to be able to find them, and many hosts can be configured only for one gateway address.