LAB: OSPF Stub Areas

-Configure Area 3 to be Stub areas to filter External type 5 routes.

Stub areas used to remove Type-5 External link states from the database and replace them with a default route.
  Note:  type 1, 2 and 3 LSA are still present inside the Stub areas. only type 4 and type 5 are not present.


command:

R5:
router ospf 1
area 3 stub

SW2:
router ospf 1
area 3 stub
 

SW4:
router ospf 1
area 3 stub

pre-verification before applying the stub commands

Rack1SW4# sho ip ospf database | begin Type-5
                Type-5 AS External Link States

Link ID         ADV Router      Age         Seq#       Checksum Tag
30.0.0.0        150.1.4.4       3     (DNA) 0x80000001 0x00D80A 0
30.1.0.0        150.1.4.4       3     (DNA) 0x80000001 0x00CC15 0
30.2.0.0        150.1.4.4       3     (DNA) 0x80000001 0x00C020 0
30.3.0.0        150.1.4.4       3     (DNA) 0x80000001 0x00B42B 0
31.0.0.0        150.1.4.4       3     (DNA) 0x80000001 0x00CB16 0
31.1.0.0        150.1.4.4       3     (DNA) 0x80000001 0x00BF21 0
31.2.0.0        150.1.4.4       3     (DNA) 0x80000001 0x00B32C 0
31.3.0.0        150.1.4.4       3     (DNA) 0x80000001 0x00A737 0
51.51.51.51     192.10.1.254    1110  (DNA) 0x8000000C 0x008677 0
54.1.1.0        150.1.6.6       4     (DNA) 0x80000001 0x000EE6 0
200.0.0.0       150.1.6.6       4     (DNA) 0x80000011 0x0093C0 0
200.0.1.0       150.1.6.6       5     (DNA) 0x80000001 0x00A8BA 0
200.0.2.0       150.1.6.6       4     (DNA) 0x80000001 0x009DC4 0
200.0.3.0       150.1.6.6       4     (DNA) 0x80000001 0x0092CE 0
204.12.1.0      150.1.4.4       3     (DNA) 0x8000000A 0x004CD1 0

Rack1SW4#show ip ospf database external 30.1.0.0

            OSPF Router with ID (150.1.10.10) (Process ID 1)

                Type-5 AS External Link States

  Routing Bit Set on this LSA
  LS age: 3 (DoNotAge)
  Options: (No TOS-capability, DC)
  LS Type: AS External Link
  Link State ID: 30.1.0.0 (External Network Number )
  Advertising Router: 150.1.4.4
  LS Seq Number: 80000001
  Checksum: 0xCC15
  Length: 36
  Network Mask: /16
        Metric Type: 2 (Larger than any link state path)
        TOS: 0
        Metric: 20
        Forward Address: 0.0.0.0
        External Route Tag: 0

Rack1SW4#show ip ospf database asbr-summary 150.1.4.4

            OSPF Router with ID (150.1.10.10) (Process ID 1)

                Summary ASB Link States (Area 3)

  Routing Bit Set on this LSA
  LS age: 2 (DoNotAge)
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(AS Boundary Router)
  Link State ID: 150.1.4.4 (AS Boundary Router address)
  Advertising Router: 150.1.5.5
  LS Seq Number: 8000000B
  Checksum: 0x4F61
  Length: 28
  Network Mask: /0
        TOS: 0  Metric: 64

after applying the stub commands.




Rack1SW4#show ip ospf database asbr-summary 150.1.4.4

            OSPF Router with ID (150.1.10.10) (Process ID 1)

Rack1SW4#show ip route 30.1.0.0
% Network not in table

Rack1SW4#show ip ospf database summary 0.0.0.0

            OSPF Router with ID (150.1.10.10) (Process ID 1)

                Summary Net Link States (Area 3)

  Routing Bit Set on this LSA
  LS age: 18 (DoNotAge)
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 0.0.0.0 (summary Network Number)
  Advertising Router: 150.1.5.5
  LS Seq Number: 80000001
  Checksum: 0x1D7F
  Length: 28
  Network Mask: /0
        TOS: 0  Metric: 1

Rack1SW4#traceroute 30.1.0.1

Type escape sequence to abort.
Tracing the route to 30.1.0.1

  1 155.1.108.8 4 msec 4 msec 4 msec
  2 155.1.58.5 12 msec 16 msec 0 msec
  3 155.1.45.4 16 msec 24 msec 4 msec
  4 204.12.1.254 16 msec *  40 msec

Rack1SW4#show ip route | include 0.0.0.0
Gateway of last resort is 155.1.108.8 to network 0.0.0.0
O*IA 0.0.0.0/0 [110/181] via 155.1.108.8, 00:22:56, Port-channel1