OSPF：LSA Type-5 转发地址探究实验
| 1.何时产生 |
| 1.1实验拓扑
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| 1.2实验需求 （1）按拓扑完成基本配置 （2）R2、R3间运行OSPF，R2上写一条静态路由，ip route 10.10.10.0 255.255.255.0，并重分发进OPSF进程 （3）指定其下一跳为31.31.12.100，观察AS External LSA中的Forwarding Address （4）将R2所连31.31.12.0网段宣告进OSPF进程，观察实验现象 （5）将静态路由只指定出口，观察实验现象 （6）静态路由指定出口加上下一跳，观察实验现象 （7）R2上创建loopback 0 2.2.2.2/24，并且在OSPF进程中重分发直连，观察实验现象 |
| 1.3实验步骤 （1）静态路由 R2(config)#ip route 10.10.10.0 255.255.255.0 31.31.12.100
R2(config-router)#redistribute static subnets
R2#show ip ospf database external | in Forward Forward Address: 0.0.0.0 此时，值被置为0.0.0.0
（2）接口参与OSPF R2(config-router)#network 31.31.12.2 0.0.0.0 a 0
R2#show ip ospf database external | include Forward Forward Address: 31.31.12.100 此时，LSA Type 5中的Forward Address继承了静态路由中该网络的下一跳，即便实际中该下一跳不存在
（3）静态路由只指定出口 R2(config)#no ip route 10.10.10.0 255.255.255.0 R2(config)#ip route 10.10.10.0 255.255.255.0 fa0/0
R2#show ip ospf database external | include Forward Forward Address: 0.0.0.0 此时，转发地址在此被置为0.0.0.0
（4）出口加上下一跳 R2(config)#no ip route 10.10.10.0 255.255.255.0 R2(config)#ip route 10.10.10.0 255.255.255.0 fa0/0 31.31.12.100
R2#show ip ospf database external | include Forward Forward Address: 31.31.12.100 再次继承
（5）创建环回口网络，重分发直连 R2(config)#inter lo 0 R2(config-if)#ip add 2.2.2.2 255.255.255.0 R2(config)#router ospf 1 R2(config-router)#redistribute connected subnets
R2#show ip ospf database external
OSPF Router with ID (2.2.2.2) (Process ID 1)
Type-5 AS External Link States
LS age: 9 Options: (No TOS-capability, DC) LS Type: AS External Link Link State ID: 2.2.2.0 (External Network Number ) Advertising Router: 2.2.2.2 LS Seq Number: 80000001 Checksum: 0x632F Length: 36 Network Mask: /24 Metric Type: 2 (Larger than any link state path) TOS: 0 Metric: 20 Forward Address: 0.0.0.0 External Route Tag: 0
LS age: 129 Options: (No TOS-capability, DC) LS Type: AS External Link Link State ID: 10.10.10.0 (External Network Number ) Advertising Router: 2.2.2.2 LS Seq Number: 80000001 Checksum: 0x28A3 Length: 36 Network Mask: /24 Metric Type: 2 (Larger than any link state path) TOS: 0 Metric: 20 Forward Address: 31.31.12.100 External Route Tag: 0 |
| 1.4实验结论 （1）重分发进OSPF进程的外部网络 ①如果原本不存在下一跳，则Forward Address为0.0.0.0，表示为通告者ASBR本身 ②如果存在下一跳： a.如果下一跳所在网段参与OSPF进程，则Forward Address将继承该下一跳 b.如果下一跳所在网段未参与OSPF进程，则Forward Address为0.0.0.0 |
| 2.原路由负载均衡 |
| 2.1实验拓扑
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| 2.2实验需求 （1）按拓扑完成基本配置 （2）R1上将EIGRP网络重分发进OSPF进程，观察LSA Type 5中的Forward Address （3）R1上将连接EIGRP域的接口加入到OSPF进程中，观察实验现象 |
| 2.3实验步骤 （1）重分发EIGRP R1#show ip route eigrp 10.0.0.0/24 is subnetted, 1 subnets D 10.10.10.0 [90/156160] via 31.31.123.3, 00:00:49, FastEthernet0/0 [90/156160] via 31.31.123.2, 00:00:49, FastEthernet0/0 R1去往10.10.10.0网络负载均衡
R1(config)#router ospf 1 R1(config-router)#redistribute eigrp 1 subnets
R1#show ip ospf database external
OSPF Router with ID (1.1.1.1) (Process ID 1)
Type-5 AS External Link States
LS age: 76 Options: (No TOS-capability, DC) LS Type: AS External Link Link State ID: 10.10.10.0 (External Network Number ) Advertising Router: 1.1.1.1 LS Seq Number: 80000001 Checksum: 0x601E Length: 36 Network Mask: /24 Metric Type: 2 (Larger than any link state path) TOS: 0 Metric: 20 Forward Address: 0.0.0.0 External Route Tag: 0
LS age: 76 Options: (No TOS-capability, DC) LS Type: AS External Link Link State ID: 31.31.123.0 (External Network Number ) Advertising Router: 1.1.1.1 LS Seq Number: 80000001 Checksum: 0x7171 Length: 36 Network Mask: /24 Metric Type: 2 (Larger than any link state path) TOS: 0 Metric: 20 Forward Address: 0.0.0.0 External Route Tag: 0 此时的Forward Address值为0.0.0.0
（2）接口参与OSPF R1(config)#router ospf 1 R1(config-router)#network 31.31.123.1 0.0.0.0 a 0
R1#sho ip rou ei 10.0.0.0/24 is subnetted, 1 subnets D 10.10.10.0 [90/156160] via 31.31.123.3, 00:00:01, FastEthernet0/0 [90/156160] via 31.31.123.2, 00:00:01, FastEthernet0/0
R1#show ip ospf database external
OSPF Router with ID (1.1.1.1) (Process ID 1)
Type-5 AS External Link States
LS age: 25 Options: (No TOS-capability, DC) LS Type: AS External Link Link State ID: 10.10.10.0 (External Network Number ) Advertising Router: 1.1.1.1 LS Seq Number: 80000002 Checksum: 0x9927 Length: 36 Network Mask: /24 Metric Type: 2 (Larger than any link state path) TOS: 0 Metric: 20 Forward Address: 31.31.123.3 External Route Tag: 0 此时只带有一个转发地址 |
| 2.4实验结论 当原路由有多个下一跳时，选择IP地址最大的作为转发地址 |
| 3.转发地址与接口网络类型 |
| 3.1实验拓扑
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| 3.2实验需求 （1）按拓扑完成基本配置 （2）R1开启OSPF进程，宣告直连网络进入OSPF，重分发RIP进入OSPF，观察LSDB （3）修改接口网络类型为Non-Broadcast，观察LSDB （4）修改接口网络类型为Point-to-Point，观察LSDB （5）修改接口网络类型为Point-to-Multipoint，观察LSDB |
| 3.3实验步骤 （1）完成需求（2） R1#show ip ospf interface f0/0 | include Network Process ID 1, Router ID 1.1.1.1, Network Type BROADCAST, Cost: 1
R1#show ip ospf database external | in Forward Forward Address: 31.31.12.2 当接口网络类型为广播时，外部路由会带上转发地址
（2）完成需求（3） R1(config-if)#ip ospf network non-broadcast
R1#show ip ospf interface f0/0 | include Network Process ID 1, Router ID 1.1.1.1, Network Type NON_BROADCAST, Cost: 1
R1#show ip ospf database external | in Forward Forward Address: 31.31.12.2 当接口网络类型为非广播时，外部路由会带上转发地址
（3）完成需求（4） R1(config-if)#ip ospf network point-to-point
R1#show ip ospf interface f0/0 | include Network Process ID 1, Router ID 1.1.1.1, Network Type POINT_TO_POINT, Cost: 1
R1#show ip ospf database external | in Forward Forward Address: 0.0.0.0 当接口网络类型为点到点时，外部路由转发地址为0.0.0.0
（4）完成需求（5） R1(config-if)#ip ospf network point-to-multipoint
R1#show ip ospf interface f0/0 | include Network Process ID 1, Router ID 1.1.1.1, Network Type POINT_TO_MULTIPOINT, Cost: 1
R1#show ip ospf database external | in Forward Forward Address: 0.0.0.0 当接口网络类型为点到多点时，外部路由转发地址为0.0.0.0
注意： 当修改为点到多点非广播类型时，现象与点到多点相同 |
| 3.4实验结论 当接口网络类型为点到多点以及点到点时，不会携带非0转发地址 |
