|  | 11.5 | The Context of Different Routing Protocols
| 11.5.3 | LAN-to-LAN routing
The network layer must understand and be able to interface with various lower layers. Routers must be capable of seamlessly handling packets encapsulated into various lower-level frames without changing the packets' Layer 3 addressing. The Figure shows an example of this with LAN-to-LAN routing. In this example, packet traffic from source Host 4 on Ethernet Network 1 needs a path to destination Host 5 on Network 2. The LAN hosts depend on the router and its consistent network addressing to find the best path. When the router checks its routing table entries, it discovers that the best path to destination Network 2 uses outgoing port To0, the interface to a token-ring LAN. Although the lower-layer framing must change as the router passes packet traffic from Ethernet on Network 1 to token-ring on Network 2, the Layer 3 addressing for source and destination remains the same. In the Figure, the destination address remains Network 2, Host 5, regardless of the different lower-layer encapsulations.