OSPF (Open Shortest Path First or First Shortest Route Free) is a routing protocol IGP (Interior Gateway Protocol) link-state used in large networks.
OSPF features:
- Metric: Cost (Bandwidth Cisco IOS).
- Administrative distance: 110.
- Fast convergence and scalability.
- Supports classless routing, VLSM and route summary.
OSPF tables:
- Database of State Liaison: Contains data (LSA’s) received from all routers in the area.
- SPF Tree: Contains the full topology of the area generated from data of the Database of State Liaison.
- Routing Table: Routing Table: Contains the best route to each destination using data from the SPF tree.
OSPF Operation:
All routers exchange their data area (LSA’s), they set up a SPF tree with the topology of the area and cost as the routing table armed with the best routes to destinations in the area.
OSPF can be set in an area or multiple areas and multiple access networks to avoid saturation of LSA’s you use a router DR (designated) and a router BDR (backup designated).
Later on, configuration examples and tutorials of each case and some OSPF-specific commands will be presented.
Configure OSPF Configuration (Basic)
Router> enable
Router # config terminal
Router (config) # router ospf 1
(Number from 1 to 65535 as Process ID, this number is awarded the admin and not have to coinidir between routers in the same area to be neighbors)
Router (config-router) # network 10.0.0.0 0.0.0.255 area 0
(Published directly connected network, if you must use the wildcard and the ID of the area must be the same for all routers in the area)
Router (config-router) # network 192.168.10.8 0.0.0.3 area 0
(Published directly connected subnet, you should always use the wildcard and the ID of the area must be the same for all routers in the area)
Of all the routing protocols covered in the CCNA, this is the most complicated configuration.