OSPF NSSA – no-summaryオプション 034

今回はOSPFのNSSAのno-summaryオプションを解説します。

 

座学

NSSAのno-summaryオプション

NSSAのABRにおいて、area <area-id> nssaコマンドのno-summaryオプションを使用することで、ABRはNSSAに対して他のAreaのルート情報を格納したLSA Type 3は広報せず、デフォルトルートを格納したLSA Type 3のみ広報します。この機能をTotally NSSAと呼び、NSSA内のLSAの情報量を大幅に削減可能です。

 

実機での動作確認

検証内容

R1のg2、R2のg2でOSPF Area 0を有効にします。
R2のg3、R3のg2でOSPF Area 2を有効にします。
Network TypeにはPoint-to-Pointを使用します。
R1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でNSSAのno-summaryオプションを設定し、状態の変化を確認します。

 

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 180.1.1.1 255.255.255.0
!
router ospf 1
 router-id 1.1.1.1
 redistribute connected subnets
 network 10.1.1.0 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 20.1.1.3 255.255.255.0
 ip ospf network point-to-point
!
router ospf 1
 router-id 3.3.3.3
 area 2 nssa
 network 20.1.1.0 0.0.0.255 area 2

 

no-summaryオプション無し

OSPFプロセスの状態確認

R2において、Area 2でNSSAが有効な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: 00:20:12.017
 Supports only single TOS(TOS0) routes
 Supports opaque LSA
 Supports Link-local Signaling (LLS)
 Supports area transit capability
 Supports NSSA (compatible with RFC 3101)
 Supports Database Exchange Summary List Optimization (RFC 5243)
 Event-log enabled, Maximum number of events: 1000, Mode: cyclic
 It is an area border and autonomous system boundary router
 Redistributing External Routes from,
 Router is not originating router-LSAs with maximum metric
 Initial SPF schedule delay 50 msecs
 Minimum hold time between two consecutive SPFs 200 msecs
 Maximum wait time between two consecutive SPFs 5000 msecs
 Incremental-SPF disabled
 Initial LSA throttle delay 50 msecs
 Minimum hold time for LSA throttle 200 msecs
 Maximum wait time for LSA throttle 5000 msecs
 Minimum LSA arrival 100 msecs
 LSA group pacing timer 240 secs
 Interface flood pacing timer 33 msecs
 Retransmission pacing timer 66 msecs
 EXCHANGE/LOADING adjacency limit: initial 300, process maximum 300
 Number of external LSA 2. Checksum Sum 0x008B19
 Number of opaque AS LSA 0. Checksum Sum 0x000000
 Number of DCbitless external and opaque AS LSA 0
 Number of DoNotAge external and opaque AS LSA 0
 Number of areas in this router is 2. 1 normal 0 stub 1 nssa
 Number of areas transit capable is 0
 External flood list length 0
 IETF NSF helper support enabled
 Cisco NSF helper support enabled
 Reference bandwidth unit is 100 mbps
    Area BACKBONE(0)
        Number of interfaces in this area is 1
        Area has no authentication
        SPF algorithm last executed 00:00:32.302 ago
        SPF algorithm executed 5 times
        Area ranges are
        Number of LSA 3. Checksum Sum 0x019B64
        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
    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 00:00:24.623 ago
        SPF algorithm executed 7 times
        Area ranges are
        Number of LSA 4. Checksum Sum 0x017BE6
        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はArea 2に対して10.1.1.0/24を格納したLSA Type 3を広報していることが確認できます。

R3

R3#show ip ospf database

            OSPF Router with ID (3.3.3.3) (Process ID 1)

                Router Link States (Area 2)

Link ID         ADV Router      Age         Seq#       Checksum Link count
2.2.2.2         2.2.2.2         1481        0x80000008 0x009137 2
3.3.3.3         3.3.3.3         62          0x80000007 0x002A9D 2

                Summary Net Link States (Area 2)

Link ID         ADV Router      Age         Seq#       Checksum
10.1.1.0        2.2.2.2         1449        0x80000006 0x0059C3

 

SPFの計算結果の確認

R3は10.1.1.0/24のみ認識していることが確認できます。

R3

R3#show ip ospf rib

            OSPF Router with ID (3.3.3.3) (Process ID 1)

                Base Topology (MTID 0)

OSPF local RIB
Codes: * - Best, > - Installed in global RIB

*>  10.1.1.0/24, Inter, cost 2, area 2
      via 20.1.1.2, GigabitEthernet2
*   20.1.1.0/24, Intra, cost 1, area 2, Connected
      via 20.1.1.3, GigabitEthernet2

 

ルーティングテーブルの確認

R3のルーティングテーブルに10.1.1.0/24のみ存在していることが確認できます。

R3

R3#show ip route ospf
      10.0.0.0/24 is subnetted, 1 subnets
O IA     10.1.1.0 [110/2] via 20.1.1.2, 00:41:57, GigabitEthernet2

 

疎通確認

R3の20.1.1.3からR1の10.1.1.1へのPingは成功し、180.1.1.1へのPingは失敗することが確認できます。

R3

R3#ping 10.1.1.1 source 20.1.1.3
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.1.1.1, timeout is 2 seconds:
Packet sent with a source address of 20.1.1.3
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/1 ms

R3#ping 180.1.1.1 source 20.1.1.3
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 180.1.1.1, timeout is 2 seconds:
Packet sent with a source address of 20.1.1.3
.....
Success rate is 0 percent (0/5)

 

no-summaryオプション有り , default-costコマンド無し

追加した設定

R2がNSSAに対して0.0.0.0/0を格納したLSA Type 3のみを広報するように、area <area-id> nssaコマンドにno-summaryオプションを追加します。

R2

router ospf 1
 area 2 nssa no-summary

 

OSPFプロセスの状態確認

show ip ospfコマンドでは、no-summaryオプションが有効なことは確認できません。

R2

R2#show ip ospf
 Routing Process "ospf 1" with ID 2.2.2.2
 Start time: 2w0d, Time elapsed: 01:05:59.133
 Supports only single TOS(TOS0) routes
 Supports opaque LSA
 Supports Link-local Signaling (LLS)
 Supports area transit capability
 Supports NSSA (compatible with RFC 3101)
 Supports Database Exchange Summary List Optimization (RFC 5243)
 Event-log enabled, Maximum number of events: 1000, Mode: cyclic
 It is an area border and autonomous system boundary router
 Redistributing External Routes from,
 Router is not originating router-LSAs with maximum metric
 Initial SPF schedule delay 50 msecs
 Minimum hold time between two consecutive SPFs 200 msecs
 Maximum wait time between two consecutive SPFs 5000 msecs
 Incremental-SPF disabled
 Initial LSA throttle delay 50 msecs
 Minimum hold time for LSA throttle 200 msecs
 Maximum wait time for LSA throttle 5000 msecs
 Minimum LSA arrival 100 msecs
 LSA group pacing timer 240 secs
 Interface flood pacing timer 33 msecs
 Retransmission pacing timer 66 msecs
 EXCHANGE/LOADING adjacency limit: initial 300, process maximum 300
 Number of external LSA 1. Checksum Sum 0x008560
 Number of opaque AS LSA 0. Checksum Sum 0x000000
 Number of DCbitless external and opaque AS LSA 0
 Number of DoNotAge external and opaque AS LSA 0
 Number of areas in this router is 2. 1 normal 0 stub 1 nssa
 Number of areas transit capable is 0
 External flood list length 0
 IETF NSF helper support enabled
 Cisco NSF helper support enabled
 Reference bandwidth unit is 100 mbps
    Area BACKBONE(0)
        Number of interfaces in this area is 1
        Area has no authentication
        SPF algorithm last executed 00:00:59.583 ago
        SPF algorithm executed 26 times
        Area ranges are
        Number of LSA 3. Checksum Sum 0x01697D
        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
    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 00:00:59.583 ago
        SPF algorithm executed 25 times
        Area ranges are
        Number of LSA 3. Checksum Sum 0x019E12
        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はArea 2に対して10.1.1.0/24を格納したLSA Type 3は生成せず、0.0.0.0/0を格納したLSA Type 3のみ広報していることが確認できます。

R3

R3#show ip ospf database

            OSPF Router with ID (3.3.3.3) (Process ID 1)

                Router Link States (Area 2)

Link ID         ADV Router      Age         Seq#       Checksum Link count
2.2.2.2         2.2.2.2         107         0x80000015 0x007744 2
3.3.3.3         3.3.3.3         1238        0x80000007 0x002A9D 2

                Summary Net Link States (Area 2)

Link ID         ADV Router      Age         Seq#       Checksum
0.0.0.0         2.2.2.2         107         0x80000001 0x00FC31

 

以下はR2が生成した0.0.0.0/0を格納したLSA Type 3になります。Metricが1なことが確認できます。

R2

R2#show ip ospf database summary 0.0.0.0 adv-router 2.2.2.2

            OSPF Router with ID (2.2.2.2) (Process ID 1)

                Summary Net Link States (Area 2)

  LS age: 95
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 0.0.0.0 (summary Network Number)
  Advertising Router: 2.2.2.2
  LS Seq Number: 80000001
  Checksum: 0xFC31
  Length: 28
  Network Mask: /0
        MTID: 0         Metric: 1

 

SPFの計算結果の確認

R3は0.0.0.0/0を認識していることが確認できます。

R3

R3#show ip ospf rib

            OSPF Router with ID (3.3.3.3) (Process ID 1)

                Base Topology (MTID 0)

OSPF local RIB
Codes: * - Best, > - Installed in global RIB

*   20.1.1.0/24, Intra, cost 1, area 2, Connected
      via 20.1.1.3, GigabitEthernet2
*>  0.0.0.0/0, Inter, cost 2, area 2
      via 20.1.1.2, GigabitEthernet2

 

ルーティングテーブルの確認

R3のルーティングテーブルに0.0.0.0/0が投入されていることが確認できます。

R3

R3#show ip route ospf
O*IA  0.0.0.0/0 [110/2] via 20.1.1.2, 00:02:17, GigabitEthernet2

 

疎通確認

R3の20.1.1.3からR1の10.1.1.1と180.1.1.1へのPingが成功することが確認できます。

R3

R3#ping 10.1.1.1 source 20.1.1.3
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.1.1.1, timeout is 2 seconds:
Packet sent with a source address of 20.1.1.3
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/1 ms

R3#ping 180.1.1.1 source 20.1.1.3
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 180.1.1.1, timeout is 2 seconds:
Packet sent with a source address of 20.1.1.3
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/1 ms

 

no-summaryオプション有り , default-costコマンド有り

追加した設定

area <area-id> nssaコマンドのno-summaryオプションによって生成される0.0.0.0/0が格納されたLSA Type 3のMetricはarea <area-id> default-cost <cost>コマンドで変更可能です。

今回はR2が生成する0.0.0.0/0を格納したLSA Type 3のMetricを50に変更します。

R2

router ospf 1
 area 2 nssa no-summary
 area 2 default-cost 50

 

LSDBの状態確認

R2が生成した0.0.0.0/0を格納したLSA Type 3のMetricが50に変化したことが確認できます。

R2

R2#show ip ospf database summary 0.0.0.0 adv-router 2.2.2.2

            OSPF Router with ID (2.2.2.2) (Process ID 1)

                Summary Net Link States (Area 2)

  LS age: 95
  Options: (No TOS-capability, DC, Upward)
  LS Type: Summary Links(Network)
  Link State ID: 0.0.0.0 (summary Network Number)
  Advertising Router: 2.2.2.2
  LS Seq Number: 80000003
  Checksum: 0xE416
  Length: 28
  Network Mask: /0
        MTID: 0         Metric: 50

 

SPFの計算結果の確認

R3のSPFの計算結果から0.0.0.0/0のCostが51に変化したことが確認できます。

R3

R3#show ip ospf rib

            OSPF Router with ID (3.3.3.3) (Process ID 1)

                Base Topology (MTID 0)

OSPF local RIB
Codes: * - Best, > - Installed in global RIB

*   20.1.1.0/24, Intra, cost 1, area 2, Connected
      via 20.1.1.3, GigabitEthernet2
*>  0.0.0.0/0, Inter, cost 51, area 2
      via 20.1.1.2, GigabitEthernet2

 

ルーティングテーブルの確認

R3のルーティングテーブル内の0.0.0.0/0のメトリックが51に変化したことが確認できます。

R3

R3#show ip route ospf
O*IA  0.0.0.0/0 [110/51] via 20.1.1.2, 00:02:17, GigabitEthernet2

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