How to Configure OSPF Router Protocol

 

Belong to a single autonomous system based on TCP/IP network as IGP expressly used to design an IETF open shortest path first (OSPF) Protocol. It was designed as a link-state protocol can be extended to all but the most complex networks.

OSPF operation created by the forming of adjacencies between routers and topology database that contains status information about all links in the OSPF network. This information includes links and interface-based type of bandwidth or by the network administrator to manually place the weights of the various interfaces. Internal path traversal cost determined by calculating the sum of the cost of each link in the database. At the lowest cost (shortest path) path is to select the best route. If there are multiple equal-cost paths, OSPF will load balance across up to 4 of these paths.

As long as the form or discard the adjacency update this database. Complete picture of the network maintained by each router adjacency of eye drops and the corrosponding links are no longer on our website all the time, from information already on your router you can quickly choose a new path. However, since it must hold a full copy of the topological database, the required memory is considerable.

In a large network, the number of links in the database can grow very large. In these cases, a single link to change the system has a significant impact on each router. Intermittantly links to our website support and unavailible all routers will result in high processor use, reduce network performance. OSPF provides a method to segment the network into several areas. These areas as described above, connected to the "backbone" (0). Area border routers, and each link state advertisement (LSA) as the backbone, describe their links to the region's unique propegate "Summary" advertizements propegating. This describes the region as a whole database in a single summary Advertisement message, thereby reducing the overhead of computing and memory usage. Were also reduced to divide the network into areas in a single router or change network effects in other countries. Only additional area paths through the router or interface must be recalculated.

Use stub zones and areas between the routing topology of the summary could also help to reduce the number of entries in the database, and needs to go further to reduce CPU and memory requirements when changes occur in the network path is recalculated. Stub zones do not receive external LSAs (those injected into OSPF via redistribution from another protocol such as RIP) does not need to maintain any links except in the State records in the stub zone.

Configure OSPF routers via multicast or unicast SPF router Hello data reporting for all (the multicast addresses 224.0.0.5) finds other OSPF routers. Hello datagram is used to form and maintain adjacencies between routers.

Adjacent cells automatically across a point-to-point link. In multiple access networks (such as an Ethernet "designated router" (DR) election. This multi-access network on the router forms adjacencies with all other routers, is responsible for the topological database for synchronization. In addition, the backup designated router (BDR) is also selected. If a failure occurs, disconnect from the network DR,BDR took over and elected the new BDR. Which reduces the traffic because each router on the network do not form an adjacency with each of the other routers. It also reduces CPU usage, in all other router cannot connect to this network through the router. "Show IP OSPF neighbor" or "show IP OSPF interface <interface>", you can decide which router is the DR and BDR.

OSPF is enabled by creating and specifying a process ID the OSPF routing process. "Network" (such as RIP or routing), run OSPF networks. At the same time, the networks area number assigned. Through the use of "neighbors" statement, implying that neighbor. Please note that a neighbor does not necessarily form an adjacency. "Show IP OSPF neighbor" exec command can be used to determine which routers are considered neighbors and link status (whether they are simple, neighbors, neighbors, neighbors, BDR and Dr). A simple OSPF configuration is shown below.

Interface Ethernet0/0
  ip address 1.1.1.1 255.255.255.0
 Interface Serial1/2
  ip address 1.1.2.1 255.255.255.0
 Interface Fddi2/0
  ip address 1.1.3.1 255.255.255.0

 router ospf 1234
  network 1.1.1.0 0.0.0.255 area 1
  network 1.1.2.0 0.0.0.255 area 2
  network 1.1.3.0 0.0.0.255 area 0

This sequence of commands configure OSPF interfaces listed on the three nodes assign area 1, Serial1/2 2, Ethernet0/0, and Fddi2/0 to the backbone area (area 0). Please note that network statement Fu Ping needed a wildcard to cover and not the network mask.

OSPF supports variable-length subnetting and routing area, although it must be configured to check. Between and into the OSPF backbone area area area. Abstract the configuration of the network is an area border router and "regional < ID> range < network shield > <network>" command. Using routing zone, can significantly reduce the topological database size reduced, need to do a course becomes inaccessible or the amount calculated when a topology change occurs. The backbone area should not be sumarized. If properly summarize all other areas, all backbone area will contain a summary of the course.

Similarly, sumarization can be done when another protocol is redistributed into OSPF with a "summary-address <network> <network mask>"