A router running a dynamic routing protocol does not only make a best path determination to a network, it also determines a new best path if the initial path becomes unusable (or if the topology changes). For these reasons, dynamic routing protocols have an advantage over static routes. Routers that use dynamic routing protocols automatically share routing information with other routers and compensate for any topology changes without involving the network administrator.
Cisco ISR routers can support a variety of dynamic IPv4 routing protocols including:
- EIGRP - Enhanced Interior Gateway Routing Protocol
- OSPF - Open Shortest Path First
- IS-IS - Intermediate System-to-Intermediate System
- RIP - Routing Information Protocol
To determine which routing protocols are supported by the IOS, use the router ? command in global configuration mode as shown in the figure.
Note: The focus of this course is on EIGRP and OSPF. RIP will be discussed only for legacy reasons; the other routing protocols supported by the IOS are beyond the scope of the CCNA certification.