Characteristics of OSPF
OSPF is an open protocol.
It is based upon SPF algorithm written by Dijkstra.
OSPF is a link state routing protocol because it sends the information of link and their states to the directly connected neighbors.
OSPF support bandwidth VLSM,multicasting and CIDR.
OSPF is a classless routing protocol.
Administrative distance of OSPF is 110 and the metric is cost.
By default OSPF will load balance on equal path and maximum can be 16 paths.
Multicast address of OSPF is 224.0.0.5 and 224.0.0.6.
224.0.0.5 is the address of all OSPF router 224.0.0.6 is only for the DR’s(DR and BDR).
OSPF router creates three tables-
Neighbor table
Topology table
Routing table
Neighbor table contain the information of directly connected network.
Topology table have the multiple path to reach at destination.
Routing table has the best path to reach the destination.
OSPF router uses the HELLO message for the discovery of new neighbor and maintenance of neighbor table.
OSPF router send HELLO message in every 10 second on point to point and BMA type network and in every 30 second in NBMA type network.
If any OSPF router unable to receive 4 HELLO message continuously from its neighbor then that neighbor will declare as dead after 40 second on BMA and after 120 second on NBMA.
Dead timer = 4 * HELLO timer
To form the neghborship following parameter must be match.
Hello timer
Dead timer
Area id number
Stub flag
Authentication
If any single parameter is not match neighboring will not form.
We can check OSPF neighbor via-
Router# show ip OSPF neighbor
OSPF work on area concept
Area is a logical group of router that has same topology or database table
With the help of area we can reduce the size of routing table and minimize CPU utilization.
We can improve the performance of the network
We can reduce the burden of administrator
At least one interface of the router belong to different area must be directly connected to Area 0 for best performance of the network.
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