Here are some important OSPF facts:

Packet Tracer doesn't allow you to configure OSPF through the GUI - everything must be done in the command-line interface (CLI).
A variety of factors are used to calculate the best path to each LAN, such as speed, cost, and path congestion.
When the OSPF configurations are made, they use a wildcard mask and an area number.
- The wildcard mask is the opposite of a subnet mask, where it uses 0-bits to indicate the network ID and 1-bits to indicate an ignoring bit.
- The area ID indicates which logical area a router is in. If devices are in the same area, they share more detailed information compared to devices not in the same area (they receive summarized information). These ares are interface-specific, and can be any area between 0 and 4294967295 (area 0 is used as a backbone area that all OSPF area must connect with).

How OSPF works

OSPF assigns unique Router IDs (RID), which allows OSPF-enabled devices to send ping packets to other OSPF-enabled devices, specifically the direct connections. These RIDs can be configured manually or assigned automatically, the latter of which will try to use the highest loopback IPv4 address or the highest interface IPv4 address. When the directly-connected devices, otherwise known as neighbors, ping each other, they exchange link-state advertisements (LSAs); this is similar to a broadcast. All of the LSAs are sent around until every device has all LSAs (aka LSA-flooding). These LSAs are used by the router to build the link-state database (LSDB). Then, the best paths are calculated using the cost of each link and create the SPF tree. The SPF is finally used to update the SPF tree, and this process is only repeated when a change is made on one of the OSPF-enabled devices.

Configuring OSPF involves
- Enabling it on the router
- and, declaring which of the directly connected networks should be advertised, and in which area (we're using area 0 because this is a small network)
Here is the configuration for R2 in our example:
- From "config" mode type:
  - router ospf 1
- This will now put you in "router config mode"
- And then specify the networks directly connected to Router 2 along with the wildcard mask
  - network 192.168.30.0 0.0.0.255 area 0
  - network 10.10.20.0 0.0.0.255 area 0