OSPF特殊區域:
R2,R3各有一個環回口通告進area0,所有的外部路由全部重分佈進OSPF進程。在R1上應該能看到4條E2路由,2條IA路由。
看下R1上EIGRP進來的兩條路由的下一跳。
2.0.0.0/32 is subnetted, 1 subnets
O E2 2.2.2.2 [110/20] via 12.0.0.2, 00:02:56, Serial1/0
22.0.0.0/32 is subnetted, 1 subnets
O E2 22.22.22.22 [110/20] via 12.0.0.2, 00:02:51, Serial1/0
看下這兩條路由的forward metric
R1(config-router)#do show ip ro 2.2.2.2
Routing entry for 2.2.2.2/32
Known via "ospf 1", distance 110, metric 20, type extern 2, forward metric 64 因爲沒有FA,將包發到始發的ASBR上。forward metric就是去往ASBR的metric,如果有forward address就是到達forward address的metric。
Last update from 12.0.0.2 on Serial1/0, 00:01:47 ago
Routing Descriptor Blocks:
* 12.0.0.2, from 2.2.2.2, 00:01:47 ago, via Serial1/0
Route metric is 20, traffic share count is 1
將area 1設爲stub區域,再看下路由
R1,R2,R4
area 1 stub
再看下R1的路由表:
2.0.0.0/32 is subnetted, 1 subnets
O E2 2.2.2.2 [110/20] via 13.0.0.3, 00:00:05, Serial1/1
22.0.0.0/32 is subnetted, 1 subnets
O E2 22.22.22.22 [110/20] via 13.0.0.3, 00:00:08, Serial1/1
100.0.0.0/32 is subnetted, 1 subnets
O IA 100.0.0.1 [110/65] via 12.0.0.2, 00:00:05, Serial1/0
看下同一條路由的forward metric
R1(config-router)#do show ip ro 2.2.2.2
Routing entry for 2.2.2.2/32
Known via "ospf 1", distance 110, metric 20, type extern 2, forward metric 65 經由R3到達R2的路由。 收到E2路由,
Last update from 13.0.0.3 on Serial1/1, 00:01:27 ago
Routing Descriptor Blocks:
* 13.0.0.3, from 2.2.2.2, 00:01:27 ago, via Serial1/1
Route metric is 20, traffic share count is 1
從多個方向收到一條E2路由的時候,AD相同的情況下,先比較 metric然後再比較forward metric(其中有FA的影響)。選路不做重點討論,在下節課會着重去講。
看下R4的路由表:
O*IA 0.0.0.0/0 [110/129] via 14.0.0.1, 00:03:22, Serial1/2
LSDB:
OSPF Router with ID (4.4.4.4) (Process ID 1)
Router Link States (Area 1)
Link ID ADV Router Age Seq# Checksum Link count
1.1.1.1 1.1.1.1 248 0x80000012 0x001E82 4
2.2.2.2 2.2.2.2 254 0x8000000C 0x00600C 2
4.4.4.4 4.4.4.4 247 0x80000004 0x002D32 2
Summary Net Link States (Area 1)
Link ID ADV Router Age Seq# Checksum
0.0.0.0 2.2.2.2 259 0x80000001 0x0075C0
13.0.0.0 2.2.2.2 259 0x80000006 0x00449F
100.0.0.1 2.2.2.2 259 0x80000006 0x004883
123.0.0.0 2.2.2.2 259 0x80000006 0x00268F
200.0.0.1 2.2.2.2 259 0x80000006 0x00392D
結論:STUB區域隔離4類LSA和5類LSA。會由ABR強制(任何兩個非骨幹區域,都不能直接通信,必須要經過骨幹區域)
totally stub:
由於3類LSA,和默認都是ABR下放的,totally只需要在ABR上做即可
R2(config-router)#area 1 stub no-summary
R4上路由表:
12.0.0.0/24 is subnetted, 1 subnets
O 12.0.0.0 [110/128] via 14.0.0.1, 00:13:40, Serial1/2
14.0.0.0/24 is subnetted, 1 subnets
C 14.0.0.0 is directly connected, Serial1/2
O*IA 0.0.0.0/0 [110/129] via 14.0.0.1, 00:01:50, Serial1/2
R4上LSDB:
OSPF Router with ID (4.4.4.4) (Process ID 1)
Router Link States (Area 1)
Link ID ADV Router Age Seq# Checksum Link count
1.1.1.1 1.1.1.1 159 0x80000013 0x001C83 4
2.2.2.2 2.2.2.2 100 0x8000000D 0x005E0D 2
4.4.4.4 4.4.4.4 821 0x80000006 0x002934 2
Summary Net Link States (Area 1)
Link ID ADV Router Age Seq# Checksum
0.0.0.0 2.2.2.2 100 0x80000003 0x0071C2
可以看出,totally stub 是隔離3,4,5類LSA,並且下放一條3類的默認路由。
NSSA:
R1,R2,R4:
area 1 nssa
看R4的路由表:
1.0.0.0/32 is subnetted, 1 subnets
O N2 1.1.1.1 [110/20] via 14.0.0.1, 00:05:06, Serial1/2
2.0.0.0/32 is subnetted, 1 subnets
O N2 2.2.2.2 [110/20] via 14.0.0.1, 00:05:06, Serial1/2
100.0.0.0/32 is subnetted, 1 subnets
O IA 100.0.0.1 [110/129] via 14.0.0.1, 00:05:06, Serial1/2
200.0.0.0/32 is subnetted, 1 subnets
O IA 200.0.0.1 [110/130] via 14.0.0.1, 00:05:06, Serial1/2
22.0.0.0/32 is subnetted, 1 subnets
O N2 22.22.22.22 [110/20] via 14.0.0.1, 00:05:06, Serial1/2
11.0.0.0/32 is subnetted, 1 subnets
O N2 11.11.11.11 [110/20] via 14.0.0.1, 00:05:06, Serial1/2
123.0.0.0/24 is subnetted, 1 subnets
O IA 123.0.0.0 [110/129] via 14.0.0.1, 00:05:07, Serial1/2
12.0.0.0/24 is subnetted, 1 subnets
O 12.0.0.0 [110/128] via 14.0.0.1, 00:05:07, Serial1/2
13.0.0.0/24 is subnetted, 1 subnets
O IA 13.0.0.0 [110/193] via 14.0.0.1, 00:05:07, Serial1/2
14.0.0.0/24 is subnetted, 1 subnets
C 14.0.0.0 is directly connected, Serial1/2
NSSA區域會將外部路由引入,用7類LSA代替5類LSA在本NSSA區域泛洪。NSSA不會下放默認路由,在R2上下放默認路由。
R2(config-router)#area 1 nssa default-information-originate
R4上看到一條N2的路由:
O*N2 0.0.0.0/0 [110/1] via 14.0.0.1, 00:00:05, Serial1/2
對於R4來說,R1是ASBR,R2是ASBR的同時也是ABR,但是R2下放了一條默認路由,訪問這個區域以外的路由,除了R1進來的路由,其他的都可以通過默認路由走。R2進來的7類LSA,完全沒有必要。
在R2上:
R2(config-router)#area 1 nssa no-redistribution
在R4上看,沒有了R2原來的兩條7類路由。
由此得出結論,NSSA區域可以隔離4,5類LSA,不會下放默認路由。
totally NSSA(CISCO私有)
R2上:
R2(config-router)#area 1 nssa no-summary
看下R4的路由表
1.0.0.0/32 is subnetted, 1 subnets
O N2 1.1.1.1 [110/20] via 14.0.0.1, 00:01:30, Serial1/2
11.0.0.0/32 is subnetted, 1 subnets
O N2 11.11.11.11 [110/20] via 14.0.0.1, 00:01:30, Serial1/2
12.0.0.0/24 is subnetted, 1 subnets
O 12.0.0.0 [110/128] via 14.0.0.1, 00:01:30, Serial1/2
14.0.0.0/24 is subnetted, 1 subnets
C 14.0.0.0 is directly connected, Serial1/2
O*IA 0.0.0.0/0 [110/129] via 14.0.0.1, 00:00:04, Serial1/2
totally NSSA會幹掉3,4,5類LSA,並且會下放一條3類的默認路由。
注:area 1 nssa no-redistribution default-information-originate no-summary 3條命令可以連用,後兩條多此一舉,3類默認路由會優於7類的默認路由。雖然LSDB裏面7類還有。