I am learning about OSPF Routing which is a dynamic routing protocol.
I have questions with regards to commands on the router:
Why do the commands end with 0.0.0.255 area 0?
What does 0.0.0.255 mean?
What does area 0 mean?
Cisco – Why do OSPF route commands end with 0.0.0.255
ciscocisco-commandsospfrouterrouting
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What does the topology look like? How are you doing routing today towards these networks? Or is the router being deployed now? Do you have an OSPF capable router connected to this router that is not running OSPF?
If you do then I suggest you redistribute static on this router. Something like:
ip prefix-list static-routes permit 10.0.0.0/24
ip prefix-list static-routes permit 10.0.10.0/24
ip prefix-list static-routes permit 10.0.20.0/24
route-map static-allowed permit 10
match ip address prefix-list static-routes
route-map static-allowed deny 20
The explicit deny at the end is not really needed as there is an implicit deny but it makes the logic a bit more clear.
Then under the OSPF process:
router ospf x
redistribute static subnets route-map static-allowed
It's important to note that type 2 LSA's are only generated on segments where a DR/BDR has been elected - this includes BMA (Broadcast Multi-Access) and NBMA (Non-Broadcast Multi-Access) networks. The DR is what generates the type 2 LSA. This behavior can be bypassed by configuring your Ethernet interfaces that you're choosing to run OSPF on as point-to-point (this will also prevent the DR election process).
Type 2 LSA's are beneficial when running OSPF over a Broadcast (Ethernet) or Non-Broadcast Multi-Access (Frame Relay) medium. Put simply, yes, the routers could use type 1 LSA's and detail every router's links to all other routers, but this is inefficient and will introduce unnecessary bloat into the OSPF LSDB. To mitigate this, the Type 2 (network) LSA is used to represent the broadcast subnet. Each router LSA then has a link to the broadcast subnet’s network LSA, and the network LSA has links to each of the router LSAs. It's a math problem - with every router using type 1 LSA's, you have n * (n - 1) links in the link state database. With type 2 LSA's, this number is reduced to n * 2.
I highly recommend reading John Moy's book on OSPF. He also wrote the initial RFC's for the protocol.
Very well explained!
Maybe this graphic help visualize that.
Best Answer
An OSPF domain is broken up into areas, and every area connects to area 0. The area portion of the command tells OSPF which area to put the interface(s) using address(es) in that range into.
The "0.0.0.255" is a wildcard mask (inverse of the prefix mask). It tells OSPF the range to use for selecting the interfaces for that network statement. The "network 10.0.1.0 0.0.0.255 area 0" means any interfaces in the 10.0.1.0/24 prefix will be in area 0.