类似海贼王之魅力无限:在一个Stub区域内存在两个ABR,他们都产生默认路由。那么会不会出现由于互指默...
来源:百度文库 编辑:偶看新闻 时间:2024/04/29 17:41:37
在一个Stub区域内存在两个ABR,他们都产生默认路由。那么会不会出现由于互指默认路由而产生环路?
先上图描述一下这个环境:
手画的比较简陋,大概能明白就行。
Area 1目前是Stub区域并且存在两个ABR。首先说明的是一般在多个ABR的情况下不太建议做Stub,尤其是Totally Stubby,这样会有次优路径的问题,不过还是允许配置的,这样就有种可能,R2和R4这两个ABR会通告Default路由下来,那么事实上R2和R4也会收到彼此通告的默认路由。这里,如果R2和R4处理不到位,那么很可能出现路由环路。但是事实上路由器对于这种情况会不会这样做呢?我们还原一下。
R2目前的配置:
不过,这个原因是什么?有什么依据?
我们简单分析一下Database
首先看看R3:
在看看R2这个ABR的LSDB:
这里ABR有个约定,如果自己是个ABR而同时它又收到同区域另一个ABR的Type-3的关于Default-route的LSA,那么这个LSA不会设置Routing-bit。不只如此,如果这个ABR收到了另一个ABR的非默认路由的LSA,它也不会使用,不过这个原因在于区域内的路由由于区域间的路由。以R4为例:
再打开其中的10.0.0.1,这一条是R1的Loopback:
这里我也很迷惑,到底是因为路由优先级的问题还是因为这条路由来自于本区域的ABR导致路由器不加入这条LSA。
没人解释,那姑且我们就找个自己能理解的办法吧。
先上图描述一下这个环境:
手画的比较简陋,大概能明白就行。
Area 1目前是Stub区域并且存在两个ABR。首先说明的是一般在多个ABR的情况下不太建议做Stub,尤其是Totally Stubby,这样会有次优路径的问题,不过还是允许配置的,这样就有种可能,R2和R4这两个ABR会通告Default路由下来,那么事实上R2和R4也会收到彼此通告的默认路由。这里,如果R2和R4处理不到位,那么很可能出现路由环路。但是事实上路由器对于这种情况会不会这样做呢?我们还原一下。
R2目前的配置:
- router ospf 1
- router-id 2.2.2.2
- log-adjacency-changes
- area 1 stub
- network 10.0.0.2 0.0.0.0 area 0
- network 10.0.12.0 0.0.0.255 area 0
- network 10.0.23.0 0.0.0.255 area 1
- router ospf 1
- router-id 4.4.4.4
- log-adjacency-changes
- area 1 stub
- network 10.0.0.4 0.0.0.0 area 0
- network 10.0.14.0 0.0.0.255 area 0
- network 10.0.34.0 0.0.0.255 area 1
- R3#show ip route ospf
- 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, + - replicated route
- Gateway of last resort is 10.0.34.4 to network 0.0.0.0
- O*IA 0.0.0.0/0 [110/65] via 10.0.34.4, 00:03:23, Serial1/3
- [110/65] via 10.0.23.2, 00:03:33, Serial1/2
- 10.0.0.0/8 is variably subnetted, 10 subnets, 2 masks
- O IA 10.0.0.1/32 [110/129] via 10.0.34.4, 00:03:23, Serial1/3
- [110/129] via 10.0.23.2, 00:03:33, Serial1/2
- O IA 10.0.0.2/32 [110/65] via 10.0.23.2, 00:03:33, Serial1/2
- O IA 10.0.0.4/32 [110/65] via 10.0.34.4, 00:03:23, Serial1/3
- O IA 10.0.12.0/24 [110/128] via 10.0.23.2, 00:03:33, Serial1/2
- O IA 10.0.14.0/24 [110/128] via 10.0.34.4, 00:03:23, Serial1/3
- R2#show ip route ospf
- 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, + - replicated route
- Gateway of last resort is not set
- 10.0.0.0/8 is variably subnetted, 10 subnets, 2 masks
- O 10.0.0.1/32 [110/65] via 10.0.12.1, 00:05:18, Serial1/2
- O 10.0.0.3/32 [110/65] via 10.0.23.3, 00:04:48, Serial1/3
- O 10.0.0.4/32 [110/129] via 10.0.12.1, 00:05:18, Serial1/2
- O 10.0.14.0/24 [110/128] via 10.0.12.1, 00:05:18, Serial1/2
- O 10.0.34.0/24 [110/128] via 10.0.23.3, 00:04:48, Serial1/3
- R4#show ip route ospf
- 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, + - replicated route
- Gateway of last resort is not set
- 10.0.0.0/8 is variably subnetted, 10 subnets, 2 masks
- O 10.0.0.1/32 [110/65] via 10.0.14.1, 00:05:34, Serial1/0.14
- O 10.0.0.2/32 [110/129] via 10.0.14.1, 00:05:34, Serial1/0.14
- O 10.0.0.3/32 [110/65] via 10.0.34.3, 00:05:14, Serial1/3
- O 10.0.12.0/24 [110/128] via 10.0.14.1, 00:05:34, Serial1/0.14
- O 10.0.23.0/24 [110/128] via 10.0.34.3, 00:05:14, Serial1/3
不过,这个原因是什么?有什么依据?
我们简单分析一下Database
首先看看R3:
- R3#show ip ospf database summ 0.0.0.0
- OSPF Router with ID (3.3.3.3) (Process ID 1)
- Summary Net Link States (Area 1)
- Routing Bit Set on this LSA in topology Base with MTID 0
- LS age: 428
- 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: 0x75C0
- Length: 28
- Network Mask: /0
- MTID: 0 Metric: 1
- Routing Bit Set on this LSA in topology Base with MTID 0
- LS age: 422
- Options: (No TOS-capability, DC, Upward)
- LS Type: Summary Links(Network)
- Link State ID: 0.0.0.0 (summary Network Number)
- Advertising Router: 4.4.4.4
- LS Seq Number: 80000001
- Checksum: 0x39F4
- Length: 28
- Network Mask: /0
- MTID: 0 Metric: 1
在看看R2这个ABR的LSDB:
- R2#show ip ospf database summ 0.0.0.0
- OSPF Router with ID (2.2.2.2) (Process ID 1)
- Summary Net Link States (Area 1)
- LS age: 514
- 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: 0x75C0
- Length: 28
- Network Mask: /0
- MTID: 0 Metric: 1
- LS age: 509
- Options: (No TOS-capability, DC, Upward)
- LS Type: Summary Links(Network)
- Link State ID: 0.0.0.0 (summary Network Number)
- Advertising Router: 4.4.4.4
- LS Seq Number: 80000001
- Checksum: 0x39F4
- Length: 28
- Network Mask: /0
- MTID: 0 Metric: 1
这里ABR有个约定,如果自己是个ABR而同时它又收到同区域另一个ABR的Type-3的关于Default-route的LSA,那么这个LSA不会设置Routing-bit。不只如此,如果这个ABR收到了另一个ABR的非默认路由的LSA,它也不会使用,不过这个原因在于区域内的路由由于区域间的路由。以R4为例:
- R4#show ip ospf database
- OSPF Router with ID (4.4.4.4) (Process ID 1)
- Router Link States (Area 0)
- Link ID ADV Router Age Seq# Checksum Link count
- 1.1.1.1 1.1.1.1 1386 0x80000003 0x008BDD 5
- 2.2.2.2 2.2.2.2 1422 0x80000003 0x00F948 3
- 4.4.4.4 4.4.4.4 1380 0x80000003 0x001E0C 3
- Summary Net Link States (Area 0)
- Link ID ADV Router Age Seq# Checksum
- 10.0.0.3 2.2.2.2 666 0x80000001 0x0039AD
- 10.0.0.3 4.4.4.4 668 0x80000001 0x00FCE1
- 10.0.23.0 2.2.2.2 1414 0x80000001 0x004F84
- 10.0.23.0 4.4.4.4 668 0x80000001 0x0095F5
- 10.0.34.0 2.2.2.2 666 0x80000001 0x005830
- 10.0.34.0 4.4.4.4 1371 0x80000001 0x009927
- Router Link States (Area 1)
- Link ID ADV Router Age Seq# Checksum Link count
- 2.2.2.2 2.2.2.2 678 0x80000004 0x0089B8 2
- 3.3.3.3 3.3.3.3 670 0x80000005 0x00B75D 5
- 4.4.4.4 4.4.4.4 671 0x80000003 0x008694 2
- Summary Net Link States (Area 1)
- Link ID ADV Router Age Seq# Checksum
- 0.0.0.0 2.2.2.2 695 0x80000001 0x0075C0
- 0.0.0.0 4.4.4.4 688 0x80000001 0x0039F4
- 10.0.0.1 2.2.2.2 695 0x80000003 0x006781
- 10.0.0.1 4.4.4.4 688 0x80000002 0x002DB4
- 10.0.0.2 2.2.2.2 695 0x80000003 0x00DA4D
- 10.0.0.2 4.4.4.4 688 0x80000002 0x00A5FA
- 10.0.0.4 2.2.2.2 695 0x80000002 0x00CDD8
- 10.0.0.4 4.4.4.4 688 0x80000003 0x008A93
- 10.0.12.0 2.2.2.2 695 0x80000003 0x00E2FB
- 10.0.12.0 4.4.4.4 688 0x80000002 0x002B6C
- 10.0.14.0 2.2.2.2 695 0x80000003 0x004F4D
- 10.0.14.0 4.4.4.4 688 0x80000003 0x009044
再打开其中的10.0.0.1,这一条是R1的Loopback:
- R4#show ip ospf database summary 10.0.0.1
- OSPF Router with ID (4.4.4.4) (Process ID 1)
- Summary Net Link States (Area 1)
- LS age: 916
- Options: (No TOS-capability, DC, Upward)
- LS Type: Summary Links(Network)
- Link State ID: 10.0.0.1 (summary Network Number)
- Advertising Router: 2.2.2.2
- LS Seq Number: 80000003
- Checksum: 0x6781
- Length: 28
- Network Mask: /32
- MTID: 0 Metric: 65
- LS age: 909
- Options: (No TOS-capability, DC, Upward)
- LS Type: Summary Links(Network)
- Link State ID: 10.0.0.1 (summary Network Number)
- Advertising Router: 4.4.4.4
- LS Seq Number: 80000002
- Checksum: 0x2DB4
- Length: 28
- Network Mask: /32
- MTID: 0 Metric: 65
这里我也很迷惑,到底是因为路由优先级的问题还是因为这条路由来自于本区域的ABR导致路由器不加入这条LSA。
没人解释,那姑且我们就找个自己能理解的办法吧。
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