循序渐进 OSPF的详细剖析（三）

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范琳琳 2009-04-03 10:01:23 博主文章分类：CISCO ©著作权

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理论性的东西，理解起来总有点难。今天我们用实验验证一下前文中有关OSPF的知识！
试验所用拓扑如下：
循序渐进 OSPF的详细剖析（三）_职场

拓扑介绍：
分为Area 0 Area 1 和Area 2三个区域。R1的全部和R2的S0/0属于Area 1；r2的S0/1和R3的S0/0属于Area 0；R3的S0/1和R4的全部属于Area 2.每个路由器都设置有一个loop端口。

试验目的：理论结合试验，更深入理解OSPF的有关知识。
好了，让我们从OSPF的网络类型开始：
OSPF的网络类型
在上一篇文章中我们提到过：根据路由器所连接的物理网络不同，OSPF将网络划分为四种类型：
点到点型（Point-to-Point）、点到多点型（Point-to-MultiPoint）、广播多路访问型（Broadcast multiAccess）、非广播多路访问型（None Broadcast MultiAccess，NBMA）

首先配置点到点的多区域的OSPF。
多区域的OSPF其实很简单，只要注意正确分配网络到特定区域就OK了！
配置步骤如下：（路由器的基本配置省略）
R1
r1(config)#router ospf 100
r1(config-router)#network 192.168.1.0 0.0.0.255 area 1 分配网络到特定区域
r1(config-router)#network 172.16.1.0 0.0.0.255 area 1
r1(config-router)#network 10.1.1.0 0.0.0.255 area 1

R2
r2(config)#router ospf 100
r2(config-router)#network 192.168.1.0 0.0.0.255 area 1 分配网络到特定区域
r2(config-router)#network 192.168.2.0 0.0.0.255 area 0
r2(config-router)#network 20.1.1.0 0.0.0.255 area1

R3
r3(config)#router ospf 100
r3(config-router)#network 192.168.2.0 0.0.0.255 area 0 分配网络到特定区域
r3(config-router)#network 192.168.3.0 0.0.0.255 area 2
r3(config-router)#network 30.1.1.0 0.0.0.255 area 0

R4
r4(config)#router ospf 100
r4(config-router)#network 192.168.3.0 0.0.0.255 area 2 分配网络到特定区域
r4(config-router)#network 172.16.100.0 0.0.0.255 area 2
r4(config-router)#network 40.1.1.0 0.0.0.255 area 2

验证点到点OSPF的配置，PC1 和PC2之间能相互通讯。配置成功！
VPCS 1 >ping 172.16.100.2
172.16.100.2 icmp_seq=1 time=69.000 ms
172.16.100.2 icmp_seq=2 time=38.000 ms
172.16.100.2 icmp_seq=3 time=54.000 ms
172.16.100.2 icmp_seq=4 time=121.000 ms
172.16.100.2 icmp_seq=5 time=56.000 ms

接下来开始验证有关OSPF的网络类型的信息！
点到点型（Point-to-Point）
show ip ospf int s0/0查看OSPF的网络类型。如下显示，路由器间的网络类型是点到点型的网络。

r1>show ip ospf int s0/0
Serial0/0 is up, line protocol is up
Internet Address 192.168.1.1/24, Area 1
Process ID 100, Router ID 10.1.1.1, Network Type POINT_TO_POINT, Cost: 64
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
    oob-resync timeout 40
    Hello due in 00:00:05
Supports Link-local Signaling (LLS)
Index 3/3, flood queue length 0
Next 0x0(0)/0x0(0)
Last flood scan length is 1, maximum is 1
Last flood scan time is 0 msec, maximum is 0 msec
Neighbor Count is 1, Adjacent neighbor count is 1
    Adjacent with neighbor 20.1.1.1
Suppress hello for 0 neighbor(s)

查看每个路由器的邻居关系数据库（邻居表）。如下，验证了在点到点网络上是不需要选举DR和BDR
R1
r1#show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface
20.1.1.1 0 FULL/ - 00:00:31 192.168.1.2 Serial0/0

R2
r2#show ip ospf neighbor

Neighbor ID     Pri   State           Dead Time   Address         Interface
30.1.1.1          0   FULL/ -        00:00:38    192.168.2.2     Serial0/1
10.1.1.1          0   FULL/ -        00:00:31    192.168.1.1     Serial0/0

R3
r3#show ip ospf neighbor

Neighbor ID     Pri   State           Dead Time   Address         Interface
20.1.1.1          0   FULL/ -        00:00:37    192.168.2.1     Serial0/0
40.1.1.1          0   FULL/ -        00:00:32    192.168.3.2     Serial0/1

R4
r4#show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface
30.1.1.1 0 FULL/ - 00:00:37 192.168.3.1 Serial0/0

点到多点型（Point-to-MultiPoint）

我们把Area 2的网络类型改变为点到多点型。更改配置命令如下：
R3
r3(config)#int s0/1
r3(config-if)#ip ospf network point-to-multipoint

R4
r4(config)#int s0/0
r4(config-if)#ip ospf network point-to-multipoint

查看OSPF网络类型，网络类型已经更改为点到多点型。

r3#show ip ospf int s0/1
Serial0/1 is up, line protocol is up
Internet Address 192.168.3.1/24, Area 2
Process ID 100, Router ID 30.1.1.1, Network Type POINT_TO_MULTIPOINT, Cost: 64

Transmit Delay is 1 sec, State POINT_TO_MULTIPOINT,
Timer intervals configured, Hello 30, Dead 120, Wait 120, Retransmit 5
    oob-resync timeout 120
    Hello due in 00:00:04
Supports Link-local Signaling (LLS)
Index 1/3, flood queue length 0
Next 0x0(0)/0x0(0)
Last flood scan length is 1, maximum is 2
Last flood scan time is 0 msec, maximum is 0 msec
Neighbor Count is 1, Adjacent neighbor count is 1
    Adjacent with neighbor 40.1.1.1
Suppress hello for 0 neighbor(s)

查看路由器的邻居关系数据库。
注意看，此处验证了在点到多点网络中也是不需要选举DR和BDR的。

R3
r3#show ip ospf neighbor

Neighbor ID     Pri   State           Dead Time   Address         Interface
20.1.1.1          0   FULL/ -        00:00:33    192.168.2.1     Serial0/0
40.1.1.1          0   FULL/ -        00:01:42    192.168.3.2     Serial0/1
R4
r4#show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface
30.1.1.1 0 FULL/ - 00:01:48 192.168.3.1 Serial0/0

广播多路访问型（Broadcast multiAccess）

我们把Area 1的网络类型改变为广播型。命令如下

R1
r1(config)#int s0/0
r1(config-if)#ip ospf network broadcast

R2
r2(config)#int s0/0
r2(config-if)#ip ospf network broadcast

查看ospf网络类型，此时的OSPF网络类型为广播型

r1#show ip ospf int s0/0
Serial0/0 is up, line protocol is up
Internet Address 192.168.1.1/24, Area 1
Process ID 100, Router ID 10.1.1.1, Network Type BROADCAST, Cost: 64
Transmit Delay is 1 sec, State BDR, Priority 1
Designated Router (ID) 20.1.1.1, Interface address 192.168.1.2
Backup Designated router (ID) 10.1.1.1, Interface address 192.168.1.1
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
    oob-resync timeout 40
    Hello due in 00:00:07
Supports Link-local Signaling (LLS)
Index 3/3, flood queue length 0
Next 0x0(0)/0x0(0)
Last flood scan length is 1, maximum is 1
Last flood scan time is 0 msec, maximum is 0 msec
Neighbor Count is 1, Adjacent neighbor count is 1
    Adjacent with neighbor 20.1.1.1 (Designated Router)
Suppress hello for 0 neighbor(s)

查看路由器的邻居表，显示的很清楚，广播型网络中是要选举DR和BDR的。

注意看：在选举DR和BDR的过程中，两个路由器的优先级都是1.所以DR和BDR是根据RID选举出来的，RID大的称为DR。
R1

r1#show ip ospf neighbor

Neighbor ID Pri State Dead Time Address Interface
20.1.1.1 1 FULL/DR 00:00:31 192.168.1.2 Serial0/0

R2
r2#show ip ospf neighbor

Neighbor ID     Pri   State           Dead Time   Address         Interface
30.1.1.1          0   FULL/ -        00:00:33    192.168.2.2     Serial0/1
10.1.1.1          1   FULL/BDR        00:00:31    192.168.1.1     Serial0/0

非广播多路访问型（None Broadcast MultiAccess，NBMA）

我们把Area 0的网络类型改为NBMA型。配置命令如下：

R2
r2(config)#int s0/1
r2(config-if)#ip ospf network non-broadcast

R3
r3(config)#int s0/0
r3(config-if)#ip ospf network non-broadcast

特别注意：在NBMA类型的网络中需要手工指定邻居
命令为：
r2(config-router)#neighbor 192.168.2.2
r3(config-router)#neighbor 192.168.2.1

查看ospf网络类型，网络类型已经改变为NBMA型
r2#show ip ospf int s0/1
Serial0/1 is up, line protocol is up
Internet Address 192.168.2.1/24, Area 0
Process ID 100, Router ID 20.1.1.1, Network Type NON_BROADCAST, Cost: 64
Transmit Delay is 1 sec, State BDR, Priority 1
Designated Router (ID) 30.1.1.1, Interface address 192.168.2.2
Backup Designated router (ID) 20.1.1.1, Interface address 192.168.2.1
Flush timer for old DR LSA due in 00:01:53
Timer intervals configured, Hello 30, Dead 120, Wait 120, Retransmit 5
    oob-resync timeout 120
    Hello due in 00:00:23
Supports Link-local Signaling (LLS)
Index 1/2, flood queue length 0
Next 0x0(0)/0x0(0)
Last flood scan length is 1, maximum is 1
Last flood scan time is 0 msec, maximum is 4 msec
Neighbor Count is 1, Adjacent neighbor count is 1
    Adjacent with neighbor 30.1.1.1 (Designated Router)
Suppress hello for 0 neighbor(s)

查看路由器的邻居表。证明在NBMA网络中也是要选举DR和BDR的。

r2#show ip ospf neighbor
Neighbor ID     Pri   State           Dead Time   Address         Interface
30.1.1.1          1   FULL/DR         00:01:46    192.168.2.2     Serial0/1
10.1.1.1          1   FULL/ -        00:00:34    192.168.1.1     Serial0/0

R3
r3#show ip ospf neighbor

Neighbor ID     Pri   State           Dead Time   Address         Interface
20.1.1.1          1   FULL/BDR        00:01:36    192.168.2.1     Serial0/0
40.1.1.1          0   FULL/ -        00:01:53    192.168.3.2     Serial0/1

验证OSPF的LSA类型
如下内容所示，
类型1（Router Link States）的LSA被扩散到区域内的所有路由器！
类型2( Net Link States)的LSA在广播和NBMA网络中生成的！

点到点网络中的LSA
r1#show ip ospf database

OSPF Router with ID (10.1.1.1) (Process ID 100)

Router Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum Link count
10.1.1.1        10.1.1.1        43          0x80000002 0x00A30C 4
20.1.1.1        20.1.1.1        44          0x80000001 0x00A4EC 2

Summary Net Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum
30.1.1.1        20.1.1.1        31          0x80000001 0x00A320
40.1.1.1        20.1.1.1        30          0x80000001 0x00A3D5
172.16.100.0    20.1.1.1        30          0x80000001 0x00F88A
192.168.2.0     20.1.1.1        41          0x80000001 0x007AFF
192.168.3.0     20.1.1.1        30          0x80000001 0x00F147

广播型网络中的LSA
R1
r1#show ip ospf database

OSPF Router with ID (10.1.1.1) (Process ID 100)

Router Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum Link count
10.1.1.1        10.1.1.1        8           0x80000004 0x0045CC 3
20.1.1.1        20.1.1.1        9           0x80000003 0x006E7B 1

Net Link States (Area 1)

Link ID ADV Router Age Seq# Checksum
192.168.1.2 20.1.1.1 9 0x80000001 0x004250

Summary Net Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum
30.1.1.1        20.1.1.1        359         0x80000001 0x00A320
40.1.1.1        20.1.1.1        165         0x80000001 0x00A3D5
172.16.100.0    20.1.1.1        165         0x80000001 0x00F88A
192.168.2.0     20.1.1.1        369         0x80000001 0x007AFF
192.168.3.1     20.1.1.1        179         0x80000001 0x006513
192.168.3.2     20.1.1.1        170         0x80000001 0x00DD59

NBMA网络中的LSA
R2
r2#show ip ospf database

OSPF Router with ID (20.1.1.1) (Process ID 100)

Router Link States (Area 0)

Link ID         ADV Router      Age         Seq#       Checksum Link count
20.1.1.1        20.1.1.1        21          0x80000004 0x007473 1
30.1.1.1        30.1.1.1        22          0x80000003 0x00B0F0 2

Net Link States (Area 0)

Link ID ADV Router Age Seq# Checksum
192.168.2.2 30.1.1.1 22 0x80000001 0x0091E1

Summary Net Link States (Area 0)

Link ID         ADV Router      Age         Seq#       Checksum
10.1.1.1        20.1.1.1        461         0x80000001 0x00A82F
40.1.1.1        30.1.1.1        622         0x80000003 0x00C2EA
172.16.1.0      20.1.1.1        461         0x80000001 0x00BB6B
172.16.100.0    30.1.1.1        622         0x80000003 0x00189F
192.168.1.0     20.1.1.1        826         0x80000001 0x0085F5
192.168.3.1     30.1.1.1        638         0x80000001 0x008826
192.168.3.2     30.1.1.1        629         0x80000001 0x00016C

Router Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum Link count
10.1.1.1        10.1.1.1        468         0x80000004 0x0045CC 3
20.1.1.1        20.1.1.1        468         0x80000003 0x006E7B 1

Net Link States (Area 1)

Link ID ADV Router Age Seq# Checksum
192.168.1.2 20.1.1.1 468 0x80000001 0x004250

Summary Net Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum
30.1.1.1        20.1.1.1        19          0x80000001 0x00A320
40.1.1.1        20.1.1.1        20          0x80000001 0x00A3D5
172.16.100.0    20.1.1.1        20          0x80000001 0x00F88A
192.168.2.0     20.1.1.1        830         0x80000001 0x007AFF
192.168.3.1     20.1.1.1        20          0x80000001 0x006513
192.168.3.2     20.1.1.1        20          0x80000001 0x00DD59

末梢区域和完全末梢区域
我们把Area2设置为末梢区域。配置命令如下：
r3(config-router)#area 2 stub
r4(config-router)#area 2 stub
末梢区域不接受AS外部的路由信息。由于我们都处于同意AS内。所以这里就不验证了！

把Area1设置为完全末梢区域。配置命令如下：
r1(config-router)#area 1 stub no-summary
r2(config-router)#area 1 stub no-summary
完全末梢区域不接受来自AS外部的路由汇总和来自AS中其他区域的汇总路由。
验证：如下所示LSA条目明显减少。这里验证了完全末梢区域的特点。
r1#show ip ospf database

OSPF Router with ID (10.1.1.1) (Process ID 100)

Router Link States (Area 1)

Link ID         ADV Router      Age         Seq#       Checksum Link count
10.1.1.1        10.1.1.1        123         0x80000009 0x00A16D 3
20.1.1.1        20.1.1.1        120         0x80000007 0x008463 1

Net Link States (Area 1)

Link ID ADV Router Age Seq# Checksum
192.168.1.2 20.1.1.1 120 0x80000004 0x005A37

Summary Net Link States (Area 1)

Link ID ADV Router Age Seq# Checksum
0.0.0.0 20.1.1.1 125 0x80000001 0x00E73F

路由汇总
我们在R4上添加loop 1 IP地址为 40.1.0.1 255.255.255.0
                          Loop2 Ip地址为40.1.2.1 255.255.255.0
                          Loop3 Ip地址为40.1.3.1 255.255.255.0
在R2上查看路由表。我们看到R2的路由表的条目很长，怎样可以减少路由条目呢？这时就用到了路由汇总。
r2#show ip route
Codes: 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

Gateway of last resort is not set

     20.0.0.0/24 is subnetted, 1 subnets
C       20.1.1.0 is directly connected, Loopback0
     172.16.0.0/24 is subnetted, 2 subnets
O       172.16.1.0 [110/65] via 192.168.1.1, 00:15:08, Serial0/0
O IA    172.16.100.0 [110/129] via 192.168.2.2, 00:15:08, Serial0/1
     40.0.0.0/32 is subnetted, 4 subnets
O IA    40.1.0.1 [110/129] via 192.168.2.2, 00:02:01, Serial0/1
O IA    40.1.1.1 [110/129] via 192.168.2.2, 00:15:08, Serial0/1
O IA    40.1.2.1 [110/129] via 192.168.2.2, 00:01:38, Serial0/1
O IA    40.1.3.1 [110/129] via 192.168.2.2, 00:01:18, Serial0/1
     10.0.0.0/32 is subnetted, 1 subnets
O       10.1.1.1 [110/65] via 192.168.1.1, 00:15:08, Serial0/0
C    192.168.1.0/24 is directly connected, Serial0/0
C    192.168.2.0/24 is directly connected, Serial0/1
     192.168.3.0/32 is subnetted, 2 subnets
O IA    192.168.3.2 [110/128] via 192.168.2.2, 00:15:10, Serial0/1
O IA    192.168.3.1 [110/64] via 192.168.2.2, 00:15:11, Serial0/1
     30.0.0.0/32 is subnetted, 1 subnets
O       30.1.1.1 [110/65] via 192.168.2.2, 00:15:26, Serial0/1

在R3上配置ABR路由汇总。配置命令如下：
r3(config-router)#area 2 range 40.1.0.0 255.255.252.0

再在路由器R2上查看路由表。注意看，汇总后的路由条目减少了，看看汇总后的地址。很实用吧！
r2#show ip route
Codes: 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

Gateway of last resort is not set

     20.0.0.0/24 is subnetted, 1 subnets
C       20.1.1.0 is directly connected, Loopback0
     172.16.0.0/24 is subnetted, 2 subnets
O       172.16.1.0 [110/65] via 192.168.1.1, 00:17:36, Serial0/0
O IA    172.16.100.0 [110/129] via 192.168.2.2, 00:17:36, Serial0/1
     40.0.0.0/22 is subnetted, 1 subnets
O IA    40.1.0.0 [110/129] via 192.168.2.2, 00:00:30, Serial0/1
     10.0.0.0/32 is subnetted, 1 subnets
O       10.1.1.1 [110/65] via 192.168.1.1, 00:17:36, Serial0/0
C    192.168.1.0/24 is directly connected, Serial0/0
C    192.168.2.0/24 is directly connected, Serial0/1
     192.168.3.0/32 is subnetted, 2 subnets
O IA    192.168.3.2 [110/128] via 192.168.2.2, 00:17:36, Serial0/1
O IA    192.168.3.1 [110/64] via 192.168.2.2, 00:17:37, Serial0/1
     30.0.0.0/32 is subnetted, 1 subnets
O       30.1.1.1 [110/65] via 192.168.2.2, 00:17:53, Serial0/1

本次试验中我们验证了：OSPF的区域类型；OSPF的网络类型;OSPF的LSA类型；末梢区域和完全末梢区域的特性以及OSPF的路由汇总。

怎么样，理论结合试验是不是会让我们对OSPF的理解更透彻呢！