OSPF area notation

In OSPF, the Area ID is a 32 bit value that identifies the OSPF area. As a 32 bit number, it can be written either as a decimal number or in dotted decimal notation (like an IPv4 address) to indicate the area. For example both of the following commands have identical results:

R2(config-router)#network 192.168.23.0 0.0.0.255 area 5
R2(config-router)#network 192.168.23.0 0.0.0.255 area 0.0.0.5

The router interprets both of these in binary anyway, so they are the same.

Notice the following:

RouterA(config-router)#network 198.51.100.0 0.0.0.255 area ?
  <0-4294967295>  OSPF area ID as a decimal value
  A.B.C.D         OSPF area ID in IP address format

The range of values in decimal is the same as the number of values in a 32 bit dotted decimal notation.