CCNP ROUTE: 11.Choosing the best OSPF routes - Inter-Area (between areas)

For routers in one area to calculate the cost of an interarea route, the process is similar:
Step 1. Calculate the intra-area cost from that router to the ABR listed in the type 3 LSA.
Step 2. Add the cost value listed in the Type 3 LSA. (This cost represents the cost from the ABR to the destination subnet.)

Consider R3's route to R12's Loopback 33 (192.168.33.33/24). R9 is the ABR between areas 0 and 3, so he advertised the network to R3:
R3#show ip ospf database                            
...
                Summary Net Link States (Area 0)

Link ID         ADV Router      Age         Seq#       Checksum
10.0.1.1        9.9.9.9         1107        0x80000001 0x00E22A
10.0.1.2        9.9.9.9         1078        0x80000001 0x005B70
10.0.1.3        9.9.9.9         1107        0x80000001 0x005179
10.0.10.10      9.9.9.9         1081        0x80000001 0x00B108
10.0.11.11      9.9.9.9         1109        0x80000001 0x009C1B
192.168.3.0     9.9.9.9         1158        0x80000002 0x00F7AC
192.168.33.33   9.9.9.9         1129        0x80000001 0x007FE2
...

The intra-area cost from R3 to R9 is the sum of outgoing interfaces costs along the path:

R3#show ip ospf interface fastEthernet 0/0
FastEthernet0/0 is up, line protocol is up
  Internet Address 192.168.0.3/29, Area 0
  Process ID 1, Router ID 3.3.3.3, Network Type BROADCAST, Cost: 10
...

R1#show ip ospf interface serial 0/0
Serial0/0 is up, line protocol is up
  Internet Address 192.168.0.21/30, Area 0
  Process ID 1, Router ID 1.1.1.1, Network Type POINT_TO_POINT, Cost: 64

So, up until now, the cost (from R3 to R9) is 10+64=74.

Now, we have to add the cost value listed in the Type 3 LSA (R9 advertised in the Type 3 LSA his cost to reach 192.168.33.33):
R3#show ip ospf database summary 192.168.33.33

            OSPF Router with ID (3.3.3.3) (Process ID 1)

                Summary Net Link States (Area 0)

  Routing Bit Set on this LSA
  LS age: 1344
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 192.168.33.33 (summary Network Number)
  Advertising Router: 9.9.9.9
  LS Seq Number: 80000001
  Checksum: 0x7FE2
  Length: 28
  Network Mask: /32
        TOS: 0  Metric: 11

So, the total cost from R3 to R12's Loopback33 is 74+11=85, as can be verified in the routing table of R3:
R3#show ip route
...
     192.168.33.0/32 is subnetted, 1 subnets
O IA    192.168.33.33 [110/85] via 192.168.0.1, 00:25:56, FastEthernet0/0

Note: "O IA" means OSPF Inter-Area route. Inter-Area routes are routes for which the subnet is known from a Type 3 summary LSA.

Rules concerning Intra-area and Interarea Routes on ABRs:
1. When choosing the best route, an intra-area route is always better than a competing interarea route, regardless of metric.
2. If an ABR learns a Type 3 LSA inside a nonbackbone area, the ABR ignores that LSA when calculating its own routes.