Categories R&S

OSPF – Implement and troubleshoot area types – Totally stubby area

Let’s follow up with the second area type which is totally stubby area.

 

Theory:

 

Totally stubby area stops inter-area (LSA 3) and external routes (LSA 5).

Since type 5 external LSAs are blocked, we can’t have an ASBR in a totally stubby area.

 

Requirements :

 

Change OSPF area 100 to a totally stubby area.

 

Diagram:

OSPF - Implement and troubleshoot area types - Totally stubby area

 

Configuration and verification:

 

Configuration is pretty straight forward as we only need to change the configuration on R10.

R10(config)#router ospf 10
R10(config-router)#area 100 stub no-summary

R10 is still neighbor with R11.

R10#sh ip ospf neigh
Neighbor ID     Pri   State           Dead Time   Address         Interface
111.111.111.111   0   FULL/  -        00:00:31    10.10.101.2     Ethernet0/2

Let’s see what’s happening with R11 routing table.

R11#              sh ip route ospf
Gateway of last resort is 10.10.101.1 to network 0.0.0.0
O*IA  0.0.0.0/0 [110/11] via 10.10.101.1, 00:03:17, Ethernet0/0

R11 is now showing only a default route to R10.

R11 OSPF database is also reduce to a minimum size.

R11#sh ip ospf database
            OSPF Router with ID (111.111.111.111) (Process ID 10)
                Router Link States (Area 10)
Link ID         ADV Router      Age         Seq#       Checksum Link count
111.111.111.111 111.111.111.111 1154        0x80000001 0x00C7FE 2
                Router Link States (Area 100)
Link ID         ADV Router      Age         Seq#       Checksum Link count
100.100.100.100 100.100.100.100 1111        0x80000003 0x00DD60 2
111.111.111.111 111.111.111.111 1145        0x80000002 0x002CE6 2
                Summary Net Link States (Area 100)
Link ID         ADV Router      Age         Seq#       Checksum
0.0.0.0         100.100.100.100 224         0x80000003 0x00E9C0

We can verify that area 100 is configure as totally stubby by checking R10.

R10#sh ip ospf | b Area 100
    Area 100
        Number of interfaces in this area is 1
        It is a stub area, no summary LSA in this area
        Generates stub default route with cost 1
        Area has no authentication
        SPF algorithm last executed 00:08:40.853 ago
        SPF algorithm executed 5 times
        Area ranges are
        Number of LSA 3. Checksum Sum 0x01F406
        Number of opaque link LSA 0. Checksum Sum 0x000000
        Number of DCbitless LSA 0
        Number of indication LSA 0
        Number of DoNotAge LSA 0
        Flood list length 0

 

When using totally stub area, we optimize further the OSPF database.

In the next post, we will finish to explore the area types.

 

Thank you for reading.

 

OSPF – Implement and troubleshoot area types – Totally stubby area