OSPF area range

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NOTE

  • area range で集約できるのは area にあるintra ルートのみ
  • area に存在するinterルートは集約できない

DIAGRAM

VERIFICATION

  • area 0 range 192.168.0.0 255.255.254.0 はできない
R3(config-router)#area 0 range 192.168.0.0 255.255.254.0
R4#sh ip ro os | b Gate
Gateway of last resort is not set
      10.0.0.0/8 is variably subnetted, 4 subnets, 2 masks
O IA     10.1.2.0/24 [110/3] via 10.3.4.3, 00:00:02, GigabitEthernet0/0
O IA     10.2.3.0/24 [110/2] via 10.3.4.3, 00:00:02, GigabitEthernet0/0
O IA  192.168.0.0/24 [110/4] via 10.3.4.3, 00:00:02, GigabitEthernet0/0
O IA  192.168.1.0/24 [110/4] via 10.3.4.3, 00:00:02, GigabitEthernet0/0
O IA  192.168.2.0/24 [110/3] via 10.3.4.3, 00:00:02, GigabitEthernet0/0
O IA  192.168.3.0/24 [110/3] via 10.3.4.3, 00:00:02, GigabitEthernet0/0
  • area 0 range 192.168.2.0 255.255.254.0 はできる
R3(config-router)#area 0 range 192.168.2.0 255.255.254.0
R4#sh ip ro os | b Gate
Gateway of last resort is not set
      10.0.0.0/8 is variably subnetted, 4 subnets, 2 masks
O IA     10.1.2.0/24 [110/3] via 10.3.4.3, 00:04:42, GigabitEthernet0/0
O IA     10.2.3.0/24 [110/2] via 10.3.4.3, 00:04:42, GigabitEthernet0/0
O IA  192.168.0.0/24 [110/4] via 10.3.4.3, 00:04:42, GigabitEthernet0/0
O IA  192.168.1.0/24 [110/4] via 10.3.4.3, 00:04:42, GigabitEthernet0/0
O IA  192.168.2.0/23 [110/3] via 10.3.4.3, 00:00:01, GigabitEthernet0/0
  • area 0 range 192.168.0.0 255.255.252.0 にして、filter-list で/24 * 2を止めると/22だけになるので経路を削減できるが、specific なintra ルートがなくなると集約経路もなくなるので、interルートへの接続性も失われてしまう。
ip prefix-list NO-ROUTE-SEND-TO-AREA2 seq 10 deny 192.168.0.0/24
ip prefix-list NO-ROUTE-SEND-TO-AREA2 seq 20 deny 192.168.1.0/24
ip prefix-list NO-ROUTE-SEND-TO-AREA2 seq 1000 permit 0.0.0.0/0 le 32
router ospf 1
 area 0 range 192.168.0.0 255.255.252.0
 area 0 filter-list prefix NO-ROUTE-SEND-TO-AREA2 out
  • specificな経路が無いとPassiveと表示される
R3#sh ip os | b Area B
    Area BACKBONE(0)
        Number of interfaces in this area is 1
        Area has no authentication
        SPF algorithm last executed 00:02:39.524 ago
        SPF algorithm executed 7 times
        Area ranges are
           192.168.0.0/22 Passive Advertise
        Area-filter NO-ROUTE-SEND-TO-AREA2 out
        Number of LSA 7. Checksum Sum 0x02B2FF
        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

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