다음과 같이 Topology로 구성되어 있는 경우, Area 1의 Network 정보가 Area 0에 있는 R1에서 어떻게 보이는지 확인해 보자. Area 1의 Network은 ‘6.6.6.6/32’, ‘10.10.36.0/24’, ‘10.10.46.0/24’, ‘10.10.56.0/24’이 있다.

  그리고, 각 Area 1의 Network은 각 ABR(R3, R4, R5)로부터 Cost가 다음과 같다.

R3 6.6.6.6/32 5+1 = 6
10.10.36.0/24 5
10.10.46.0/24 5+10 = 15
10.10.56.0/24 5+7 = 12
R4 6.6.6.6/32 10+1 = 11
10.10.36.0/24 10+5 = 15
10.10.46.0/24 10
10.10.56.0/24 10+7 = 17
R5 6.6.6.6/32 7+1 = 8
10.10.36.0/24 7+5 = 12
10.10.46.0/24 7+10 = 17
10.10.56.0/24 7

  이 정보를 R1에서 보면 다음과 같이 나타난다.

R1#show ip ospf database summary 6.6.6.6

            OSPF Router with ID (1.1.1.1) (Process ID 1)

                Summary Net Link States (Area 0)

  LS age: 350
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 6.6.6.6 (summary Network Number)
  Advertising Router: 3.3.3.3
  LS Seq Number: 80000001
  Checksum: 0x56BC
  Length: 28
  Network Mask: /32
        MTID: 0         Metric: 6 

  LS age: 335
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 6.6.6.6 (summary Network Number)
  Advertising Router: 4.4.4.4
  LS Seq Number: 80000001
  Checksum: 0x6A9F
  Length: 28
  Network Mask: /32
        MTID: 0         Metric: 11 

  LS age: 253
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 6.6.6.6 (summary Network Number)
  Advertising Router: 5.5.5.5
  LS Seq Number: 80000001
  Checksum: 0x2EDA
  Length: 28
  Network Mask: /32
        MTID: 0         Metric: 8 
R1#show ip ospf database summary 10.10.36.0

            OSPF Router with ID (1.1.1.1) (Process ID 1)

                Summary Net Link States (Area 0)

  LS age: 773
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 10.10.36.0 (summary Network Number)
  Advertising Router: 3.3.3.3
  LS Seq Number: 80000001
  Checksum: 0xD81B
  Length: 28
  Network Mask: /24
        MTID: 0         Metric: 5 

  LS age: 465
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 10.10.36.0 (summary Network Number)
  Advertising Router: 4.4.4.4
  LS Seq Number: 80000001
  Checksum: 0x1FC6
  Length: 28
  Network Mask: /24
        MTID: 0         Metric: 15 

  LS age: 384
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 10.10.36.0 (summary Network Number)
  Advertising Router: 5.5.5.5
  LS Seq Number: 80000001
  Checksum: 0xE202
  Length: 28
  Network Mask: /24
        MTID: 0         Metric: 12 
R1#show ip ospf database summary 10.10.46.0

            OSPF Router with ID (1.1.1.1) (Process ID 1)

                Summary Net Link States (Area 0)

  LS age: 497
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 10.10.46.0 (summary Network Number)
  Advertising Router: 3.3.3.3
  LS Seq Number: 80000001
  Checksum: 0xCE11
  Length: 28
  Network Mask: /24
        MTID: 0         Metric: 15 

  LS age: 713
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 10.10.46.0 (summary Network Number)
  Advertising Router: 4.4.4.4
  LS Seq Number: 80000001
  Checksum: 0x7E62
  Length: 28
  Network Mask: /24
        MTID: 0         Metric: 10 

  LS age: 410
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 10.10.46.0 (summary Network Number)
  Advertising Router: 5.5.5.5
  LS Seq Number: 80000001
  Checksum: 0xA62F
  Length: 28
  Network Mask: /24
        MTID: 0         Metric: 17
R1#show ip ospf database summary 10.10.56.0

            OSPF Router with ID (1.1.1.1) (Process ID 1)

                Summary Net Link States (Area 0)

  LS age: 502
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 10.10.56.0 (summary Network Number)
  Advertising Router: 3.3.3.3
  LS Seq Number: 80000001
  Checksum: 0x4296
  Length: 28
  Network Mask: /24
        MTID: 0         Metric: 12 

  LS age: 492
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 10.10.56.0 (summary Network Number)
  Advertising Router: 4.4.4.4
  LS Seq Number: 80000002
  Checksum: 0x547A
  Length: 28
  Network Mask: /24
        MTID: 0         Metric: 17 

  LS age: 470
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 10.10.56.0 (summary Network Number)
  Advertising Router: 5.5.5.5
  LS Seq Number: 80000001
  Checksum: 0xD302
  Length: 28
  Network Mask: /24
        MTID: 0         Metric: 7

  해당 Network을 ABR이 Advertise 했다고 표시되어 있기 때문에 R1은 다음과 같이 Topology를 그리게 된다.

그리고, R1에서 Area 0에 대해 SPF 계산을 하면 다음과 같은 Topology가 그려진다.

그럼 Area 1 Network에 대해 Best-Path는 다음과 같다.

6.6.6.6/32 R3 6+6 = 12
R4 3+11 = 14
R5 3+8 = 11 (Best)
10.10.36.0/24 R3 6+5 = 11 (Best)
R4 3+15 = 18
R5 3+12 = 15
10.10.46.0/24 R3 6+15 = 21
R4 3+10 = 13 (Best)
R5 3+17 = 20
10.10.56.0/24 R3 6+12 = 18
R4 3+17 = 20
R5 3+7 = 10 (Best)

  이 정보를 R1에서 보면 다음과 같이 나타난다.

R1#show ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area 
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2
       i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
       ia - IS-IS inter area, * - candidate default, U - per-user static route
       o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
       a - application route
       + - replicated route, % - next hop override, p - overrides from PfR

Gateway of last resort is not set

O IA     6.6.6.6 [110/11] via 10.10.12.2, 00:27:06, GigabitEthernet4
O IA     10.10.36.0/24 [110/11] via 10.10.13.3, 00:32:58, GigabitEthernet1
O IA     10.10.46.0/24 [110/13] via 10.10.12.2, 00:30:37, GigabitEthernet4
O IA     10.10.56.0/24 [110/10] via 10.10.12.2, 00:27:41, GigabitEthernet4

  동일한 방식으로 Area 2에 대하여 Topology를 그리면 다음과 같다.

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