OSPF(Open Shortest path first)- CCNA

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OSPF

  •  OSPF stand for Open Shortest path first
  • It uses SPF (shortest path first) or Dijkstra algorithm
  • Standard protocol.It’s a link state protocol
  • Unlimited hop count
  • Metric is cost (cost=10 ^8/B.W.)
  •  Administrative distance is 110
  • It is a classless routing protocol
  • It supports VLSM and CIDR
  •  It supports only equal cost load balancing 
  • Introduces the concept of Area’s to ease management and control traffic
  • Must have one area called as area 0
  • All the areas must connect to area 0
  •  Scales better than Distance Vector Routing protocols.
  •  Supports Authentication
  •  Updates are sent through multicast address 224.0.0.5 
  • Sends Hello packet every 10 seconds
  •  Trigger/Incremental updates
  •  Router’s send only changes in updates and not the entire routing tables in periodic
    updates
ospf

Router ID
The highest IP address of the active physical interface of the router is Router ID.
If logical interface is configured, the highest IP address of the logical interface is Router ID 


Router Types
 
In OSPF depending upon the network design and configuration, we have different types of routers.


Internal Routers are routers whose interfaces all belong to the same area. These routers have a single Link State Database.


Area Border Routers (ABR) It connects one or more areas to the backbone area and has at
least one interface that belongs to the backbone, Backbone Router Area 0 routers


Autonomous System Boundary Router (ASBR) Router participating in OSPF and other
protocols (like RIP, EIGRP and BGP)


OSPF maintains three tables :
 
1) Neighbor Table: it contains information about the directly connected ospf neighbors forming the adjacency.


2) Database table: it contains information about the entire view of the topology with respect to each router.

3) Routing information Table: it contains information about the best path calculated by the shortest path first algorithm in the database table.

SyntaxConfiguring OSPF
Router(config)# router ospf <pid>
Router(config-router)# network <Network ID> <wildcard mask> area <area id>
Example:

ROUTER 1
 
Router #config terminal
Router(config) # router ospf 100
Router(config-router) # network 10.0.0.0 0.255.255.255 area 0
Router(config-router) # network 192.168.1.0 0.255.255.255 area 0 
Router(config-router) # exit
 Router(config) # exit

Router # show ip route 
Router  # show ip ospf database 
Router  # show ip ospf neighbors

 ROUTER 2


Router #config terminal
Router(config) # router ospf 200
Router(config-router) # network 10.0.0.0 0.255.255.255 area1
Router(config-router) # network 192.168.2.0 0.255.255.255 area 1
Router(config-router) # exit 
Router (config) # exit

Router # show ip route 
Router  # show ip ospf database 
Router # show ip ospf neighbors

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