When you configure a summary address, Cisco NX-OS automatically configures a discard route for the summary address to prevent routing black holes and route loops.
OSPFv2 has the following configuration guidelines and limitations:
You can have up to four instances of OSPFv2 in a VDC.
Cisco NX-OS displays areas in dotted decimal notation regardless of whether you enter the area in decimal or dotted decimal notation.
All OSPFv2 routers must operate in the same RFC compatibility mode. OSPFv2 for Cisco NX-OS complies with RFC 2328. Use the rfc1583compatibility command in router configuration mode if your network includes routers that support only RFC 1583.
You must configure RFC 1583 compatibility on any VRF that connects to routers running only RFC1583 compatible OSPF.
Reference bandwidth for link cost calculation
OSPFv2 requires an Enterprise Services license. For a complete explanation of the Cisco NX-OS licensing scheme and how to obtain and apply licenses, see the Cisco NX-OS Licensing Guide.
nexus7009(config)# feature ospf
Nexus7009(config-if)# ip router ospf 201 area 0.0.0.15
Routing Summarization is a major factor in the success of designing your network. To ensure that your network can scale properly, route summarization is the biggest factor against which to measure your success. Without summarization, you have a flat address design with specific route information for every subnet being transmitted across the network—a bad thing in large networks.
The six time-proven steps to designing a network are as follows:
A dynamic routing protocol supports a routed protocol and maintains routing tables.
The most common use of static routes is in stub networks.
In Link-State routing protocols, each router sends only that portion of the routing table that describes the state of its own links.
Link-state protocols are based on the distributed map concept, which means that every router has a copy of the network map that is regularly updated.
The principle of link-state routing is that all the routers within an area maintain an identical copy of the network topology.
Link-state protocols such as OSPF flood all the routing information when they first become active in link-state packets. After the network converges, they send only small updates via link-state packets.
In OSPF, because each router knows the complete topology of the network, the use of the SPF algorithm creates an extremely fast convergence.
Sends updates to tables only, instead of entire tables, to routers.
Is a more economical routing protocol than RIP over time because it involves less network traffic.
During an external convergence event, OSPF could flood more traffic than RIP. Consider that RIP carries 25 routes per update; on the other hand, OSPF floods a single LSA per external route that is affected by the convergence event.
Distance vector means that information sent from router to router is based on an entry in a routing table that consists of the distance and vector to destination—distance being what it “costs” to get there and vector being the “direction” to get to the destination.
Call for each router to send its entire routing table, but only to its neighbors. The neighbor then forwards its entire routing table to its neighbors, and so.