shangban 发表于 2012-10-8 11:04:52

OSPF:LSA Type-5 转发地址探究实验


1.何时产生
1.1实验拓扑
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OSPFR2(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 10.10.10.0 255.255.255.0R2(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 10.10.10.0 255.255.255.0R2(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 0R2(config-if)#ip   add 2.2.2.2 255.255.255.0R2(config)#router   ospf 1R2(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: 9Options: (No TOS-capability, DC)LS Type: AS External LinkLink State ID: 2.2.2.0 (External   Network Number )Advertising Router: 2.2.2.2LS Seq Number: 80000001Checksum: 0x632FLength: 36Network 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: 129Options: (No TOS-capability, DC)LS Type: AS External LinkLink State ID:   10.10.10.0 (External Network Number )Advertising Router: 2.2.2.2LS Seq Number: 80000001Checksum: 0x28A3Length: 36Network 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
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EIGRPR1#show ip route eigrp   10.0.0.0/24 is subnetted, 1 subnetsD       10.10.10.0    via 31.31.123.3, 00:00:49,   FastEthernet0/0                            via 31.31.123.2, 00:00:49,   FastEthernet0/0R1去往10.10.10.0网络负载均衡
R1(config)#router   ospf 1R1(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: 76Options: (No TOS-capability, DC)LS Type: AS External LinkLink State ID: 10.10.10.0 (External Network Number )Advertising Router: 1.1.1.1LS Seq Number: 80000001Checksum: 0x601ELength: 36Network 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: 76Options: (No TOS-capability, DC)LS Type: AS External LinkLink State ID: 31.31.123.0 (External   Network Number )Advertising Router: 1.1.1.1LS Seq Number: 80000001Checksum: 0x7171Length: 36Network 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OSPFR1(config)#router   ospf 1R1(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 subnetsD       10.10.10.0 via 31.31.123.3, 00:00:01, FastEthernet0/0                            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: 25Options: (No TOS-capability, DC)LS Type: AS External LinkLink State ID:   10.10.10.0 (External Network Number )Advertising Router: 1.1.1.1LS Seq Number: 80000002Checksum: 0x9927Length: 36Network 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
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 NetworkProcess 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 NetworkProcess 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 NetworkProcess 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 NetworkProcess 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


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