OSPF NSSA – Translatorの選択 038

今回はOSPFのNSSAにABRが複数存在する場合の動作について解説します。

 

座学

NSSAのTranslatorについて

NSSAにABRが複数存在する場合、Router IDの大きいABRがLSA Type 7をLSA Type 5に変換します。

 

また、LSA Type 7からLSA Type 5への変換する役割を特定のルータに割り当てることも可能です。また、静的に役割を割り当てる際に使用するパラメータのことをNSSATranslatorRoleと呼びます。

 

NSSATranslatorRoleが割り当てられたルータは自身が生成するLSA Type 1のNSSATranslatorRole bitに1をセットします。

 

実機での動作確認

検証内容

R1のg2とg3、R2のg2、R3のg2でOSPF Area 0を有効にします。
R2のg3、R3のg3、R4のg2とg3でOSPF Area 2を有効にします。
R2のRouter IDを2.2.2.2、R3のRouter IDを3.3.3.3とします。
Network TypeにはPoint-to-Pointを使用します。
R4でOSPFに対してConnected Routeである180.1.1.0/24を再配送します。
Area 2でNSSAを有効化します。

R2とR3のどちらがLSA Type 7をLSA Type 5に変換するか確認します。

 

初期設定


interface GigabitEthernet2
 ip address 10.1.1.1 255.255.255.0
 ip ospf network point-to-point
!
interface GigabitEthernet3
 ip address 10.2.2.1 255.255.255.0
 ip ospf network point-to-point
!
router ospf 1
 router-id 1.1.1.1
 network 10.1.1.0 0.0.0.255 area 0
 network 10.2.2.0 0.0.0.255 area 0
            


interface GigabitEthernet2
 ip address 10.1.1.2 255.255.255.0
 ip ospf network point-to-point
!
interface GigabitEthernet3
 ip address 20.1.1.2 255.255.255.0
 ip ospf network point-to-point
!
router ospf 1
 router-id 2.2.2.2
 area 2 nssa
 network 10.1.1.0 0.0.0.255 area 0
 network 20.1.1.0 0.0.0.255 area 2
            


interface GigabitEthernet2
 ip address 10.2.2.3 255.255.255.0
 ip ospf network point-to-point
!
interface GigabitEthernet3
 ip address 20.2.2.3 255.255.255.0
 ip ospf network point-to-point
!
router ospf 1
 router-id 3.3.3.3
 area 2 nssa
 network 10.2.2.0 0.0.0.255 area 0
 network 20.2.2.0 0.0.0.255 area 2
            


interface GigabitEthernet2
 ip address 20.1.1.4 255.255.255.0
 ip ospf network point-to-point
!
interface GigabitEthernet3
 ip address 20.2.2.4 255.255.255.0
 ip ospf network point-to-point
!
interface GigabitEthernet4
 ip address 190.1.1.4 255.255.255.0
!
router ospf 1
 router-id 4.4.4.4
 area 2 nssa
 redistribute connected
 network 20.1.1.0 0.0.0.255 area 2
 network 20.2.2.0 0.0.0.255 area 2

 

NSSATranslatorRoleの指定無し

OSPFプロセスの状態確認

R3がLSA Type 7をLSA Type 5に変換していることが確認できます。

R2

R2#show ip ospf
 Routing Process "ospf 1" with ID 2.2.2.2
 Start time: 2w0d, Time elapsed: 00:06:11.557
    .
    <一部省略>
    .
    Area 2
        Number of interfaces in this area is 1
        It is a NSSA area
        Area has no authentication
        SPF algorithm last executed 00:00:11.450 ago
        SPF algorithm executed 9 times
        Area ranges are
        Number of LSA 8. Checksum Sum 0x031DE2
        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
R3

R3#show ip ospf
 Routing Process "ospf 1" with ID 3.3.3.3
 Start time: 2w0d, Time elapsed: 00:05:39.907
    .
    <一部省略>
    .
    Area 2
        Number of interfaces in this area is 1
        It is a NSSA area
        Perform type-7/type-5 LSA translation
        Area has no authentication
        SPF algorithm last executed 00:00:28.764 ago
        SPF algorithm executed 5 times
        Area ranges are
        Number of LSA 8. Checksum Sum 0x031DE2
        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

 

LSDBの状態確認

R3が190.1.1.0/24を格納したLSA Type 7をLSA Type 5に変換していることが確認できます。

R1

R1#show ip ospf database external 190.1.1.0

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

                Type-5 AS External Link States

  LS age: 197
  Options: (No TOS-capability, DC, Upward)
  LS Type: AS External Link
  Link State ID: 190.1.1.0 (External Network Number )
  Advertising Router: 3.3.3.3
  LS Seq Number: 80000001
  Checksum: 0xEA9
  Length: 36
  Network Mask: /24
        Metric Type: 2 (Larger than any link state path)
        MTID: 0
        Metric: 20
        Forward Address: 20.2.2.4
        External Route Tag: 0

 

R2が生成したLSA Type 1のNt bitに0がセットされていることが確認できます。

R4

R4#show ip ospf database router adv-router 2.2.2.2

            OSPF Router with ID (4.4.4.4) (Process ID 1)

                Router Link States (Area 2)

  LS age: 387
  Options: (No TOS-capability, DC)
  LS Type: Router Links
  Link State ID: 2.2.2.2
  Advertising Router: 2.2.2.2
  LS Seq Number: 80000006
  Checksum: 0xB70F
  Length: 48
  Area Border Router
  AS Boundary Router
  Number of Links: 2

    Link connected to: another Router (point-to-point)
     (Link ID) Neighboring Router ID: 4.4.4.4
     (Link Data) Router Interface address: 20.1.1.2
      Number of MTID metrics: 0
       TOS 0 Metrics: 1

    Link connected to: a Stub Network
     (Link ID) Network/subnet number: 20.1.1.0
     (Link Data) Network Mask: 255.255.255.0
      Number of MTID metrics: 0
       TOS 0 Metrics: 1

 

R3が生成したLSA Type 1のNt bitに0がセットされていることが確認できます。

R4

R4#show ip ospf database router adv-router 3.3.3.3

            OSPF Router with ID (4.4.4.4) (Process ID 1)

                Router Link States (Area 2)

  LS age: 342
  Options: (No TOS-capability, DC)
  LS Type: Router Links
  Link State ID: 3.3.3.3
  Advertising Router: 3.3.3.3
  LS Seq Number: 80000009
  Checksum: 0xB501
  Length: 48
  Area Border Router
  AS Boundary Router
  Number of Links: 2

    Link connected to: another Router (point-to-point)
     (Link ID) Neighboring Router ID: 4.4.4.4
     (Link Data) Router Interface address: 20.2.2.3
      Number of MTID metrics: 0
       TOS 0 Metrics: 1

    Link connected to: a Stub Network
     (Link ID) Network/subnet number: 20.2.2.0
     (Link Data) Network Mask: 255.255.255.0
      Number of MTID metrics: 0
       TOS 0 Metrics: 1

 

NSSATranslatorRoleの指定有り

R2にNSSATranslatorRoleを割り当てます。

追加した設定

ルータにNSSATranslatorRoleを割り当てるにはarea <area-id> nssaコマンドのtranslate type7 alwaysオプションを使用します。

R2

router ospf 1
 area 2 nssa translate type7 always

 

OSPFプロセスの状態確認

R2にNSSATranslatorRoleが割り当てられていること、また、R2がLSA Type 7をLSA Type 5に変換していることが確認できます。

R2

R2#show ip ospf
 Routing Process "ospf 1" with ID 2.2.2.2
 Start time: 2w0d, Time elapsed: 00:06:11.557
    .
    <一部省略>
    .
    Area 2
        Number of interfaces in this area is 1
        It is a NSSA area
        Configured to translate Type-7 LSAs
        Perform type-7/type-5 LSA translation
        Area has no authentication
        SPF algorithm last executed 00:01:25.227 ago
        SPF algorithm executed 12 times
        Area ranges are
        Number of LSA 8. Checksum Sum 0x03529F
        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
R3

R3#show ip ospf
 Routing Process "ospf 1" with ID 3.3.3.3
 Start time: 2w0d, Time elapsed: 00:05:39.907
    .
    <一部省略>
    .
    Area 2
        Number of interfaces in this area is 1
        It is a NSSA area
        Area has no authentication
        SPF algorithm last executed 00:02:14.151 ago
        SPF algorithm executed 9 times
        Area ranges are
        Number of LSA 8. Checksum Sum 0x03529F
        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

 

LSDBの状態確認

R2が190.1.1.0/24を格納したLSA Type 7をLSA Type 5に変換していることが確認できます。

R1

R1#show ip ospf database external 190.1.1.0

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

                Type-5 AS External Link States

  LS age: 197
  Options: (No TOS-capability, DC, Upward)
  LS Type: AS External Link
  Link State ID: 190.1.1.0 (External Network Number )
  Advertising Router: 2.2.2.2
  LS Seq Number: 80000001
  Checksum: 0x2C8F
  Length: 36
  Network Mask: /24
        Metric Type: 2 (Larger than any link state path)
        MTID: 0
        Metric: 20
        Forward Address: 20.2.2.4
        External Route Tag: 0

 

R2が生成したLSA Type 1のNt bitに1がセットされていることが確認できます。

R4

R4#show ip ospf database router adv-router 2.2.2.2

            OSPF Router with ID (4.4.4.4) (Process ID 1)

                Router Link States (Area 2)

  LS age: 13
  Options: (No TOS-capability, DC)
  LS Type: Router Links
  Link State ID: 2.2.2.2
  Advertising Router: 2.2.2.2
  LS Seq Number: 80000005
  Checksum: 0xE9CD
  Length: 48
  Area Border Router
  AS Boundary Router
  Unconditional NSSA translator
  Number of Links: 2

    Link connected to: another Router (point-to-point)
     (Link ID) Neighboring Router ID: 4.4.4.4
     (Link Data) Router Interface address: 20.1.1.2
      Number of MTID metrics: 0
       TOS 0 Metrics: 1

    Link connected to: a Stub Network
     (Link ID) Network/subnet number: 20.1.1.0
     (Link Data) Network Mask: 255.255.255.0
      Number of MTID metrics: 0
       TOS 0 Metrics: 1

 

R3が生成したLSA Type 1のNt bitに0がセットされていることが確認できます。

R4

R4#show ip ospf database router adv-router 3.3.3.3

            OSPF Router with ID (4.4.4.4) (Process ID 1)

                Router Link States (Area 2)

  LS age: 342
  Options: (No TOS-capability, DC)
  LS Type: Router Links
  Link State ID: 3.3.3.3
  Advertising Router: 3.3.3.3
  LS Seq Number: 80000005
  Checksum: 0xBDFC
  Length: 48
  Area Border Router
  AS Boundary Router
  Number of Links: 2

    Link connected to: another Router (point-to-point)
     (Link ID) Neighboring Router ID: 4.4.4.4
     (Link Data) Router Interface address: 20.2.2.3
      Number of MTID metrics: 0
       TOS 0 Metrics: 1

    Link connected to: a Stub Network
     (Link ID) Network/subnet number: 20.2.2.0
     (Link Data) Network Mask: 255.255.255.0
      Number of MTID metrics: 0
       TOS 0 Metrics: 1

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