This chapter describes how to configure On-Demand Routing (ODR). For a complete
description of the ODR commands in this chapter, refer to Chapter
6, “On-Demand Routing Commands.” To locate documentation
of other commands in this chapter, you can search online at www.cisco.com.
ODR is a feature that provides IP routing for stub sites with minimum
overhead. The overhead of a general, dynamic routing protocol is avoided without
incurring the configuration and management overhead of static routing.
A stub router can be thought of as a spoke router in a hub-and-spoke network topology,
where the only router to which the spoke is adjacent is the hub router. In
such a network topology, the IP routing information required to represent
this topology is fairly simple. These stub routers commonly have a WAN connection
to the hub router, and a small number of LAN network segments (stub
networks) are directly connected to the stub router.
These stub networks might consist only of end systems and the stub router
and, thus, do not require the stub router to learn any dynamic IP routing
information. The stub routers can then be configured with a default route
that directs IP traffic to the hub router.
To provide full connectivity, the hub router can be statically configured
to know that a particular stub network is reachable via a particular stub
router. However, if there are multiple hub routers, many stub networks, or
asynchronous connections between hubs and spokes, statically configuring the
stub networks on the hub routers becomes a problem.