A logical router is a configured partition of a traditional network hardware, or "physical," router. It replicates the hardware's functionality, creating multiple routing domains within a single router. Logical routers perform a subset of the tasks that can be handled by the physical router, and each can contain multiple routing instances and routing tables. Using logical routers can be an effective way to maximize router usage, because a set of logical routers within a single physical router can perform the operations previously performed by several pieces of equipment.
Logical routers can work independently with most internetworking protocols, including OSPF (Open Shortest Path First), RIP (Routing Information Protocol), BGP (Border Gateway Protocol), RSVP (Resource Reservation Protocol), MPLS (Multiprotocol Label Switching), and various multicast protocols. They are able to interface with such networking transmissions standards and technologies as SONET (Synchronous Optical Network), ATM (asynchronous transfer mode), Ethernet, and multilink bundled services.
Depending on the hardware vendor, some services -- such as firewall filtering, policy-based accounting, and Class of Service, usage and forwarding -- cannot be implemented for a specific logical router and must be configured at the physical router level.
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