问题描述：
1、R1和R4的环回口均不参与路由协议，作为直连接口即可
2、R1到R4环回口实现负载均衡，即可以从R2到达，也可从R3到达
3、R4到R1环回口实现负载均衡，即可以从R2到达，也可从R3到达
思考：重分布时要注意避免环路，怎样设置重分布中的metic值比较好？
实验现象及分析：
当只把ospf重分布进eigrp时，R4路由表显示如下：
R4#show ip route
Gateway of last resort is not set
     1.0.0.0/24 is subnetted, 1 subnets
D EX    1.1.1.0 [170/284160] via 10.234.0.2, 00:01:45, FastEthernet0/0
                [170/284160] via 10.234.0.3, 00:00:40, FastEthernet0/0
     4.0.0.0/24 is subnetted, 1 subnets
C       4.4.4.0 is directly connected, Loopback0
     10.0.0.0/24 is subnetted, 1 subnets
C       10.234.0.0 is directly connected, FastEthernet0/0
     12.0.0.0/30 is subnetted, 1 subnets
D EX    12.0.0.0 [170/284160] via 10.234.0.2, 00:01:45, FastEthernet0/0
                 [170/284160] via 10.234.0.3, 00:00:39, FastEthernet0/0
     13.0.0.0/30 is subnetted, 1 subnets
D EX    13.0.0.0 [170/284160] via 10.234.0.2, 00:01:45, FastEthernet0/0
                 [170/284160] via 10.234.0.3, 00:00:39, FastEthernet0/0
由R4路由表可知，到达R1环回口可以通过R2或R3两条路径。
现在把eigrp重分布进ospf中后，R1路由表显示如下：
R1#show ip route
Gateway of last resort is not set
     1.0.0.0/24 is subnetted, 1 subnets
C       1.1.1.0 is directly connected, Loopback0
     4.0.0.0/24 is subnetted, 1 subnets
O E2    4.4.4.0 [110/20] via 12.0.0.2, 00:00:38, Serial0/0/0
     10.0.0.0/24 is subnetted, 1 subnets
O E2    10.234.0.0 [110/20] via 13.0.0.2, 00:00:04, Serial0/0/1
     12.0.0.0/30 is subnetted, 1 subnets
C       12.0.0.0 is directly connected, Serial0/0/0
     13.0.0.0/30 is subnetted, 1 subnets
C       13.0.0.0 is directly connected, Serial0/0/1
由R1路由表可知，R1到达R4环回口只能通过R2，此时并没有实现负载均衡，原因何在？
看看R3的路由表先：
R3#show ip route
Gateway of last resort is not set
     1.0.0.0/24 is subnetted, 1 subnets
O E2    1.1.1.0 [110/20] via 13.0.0.1, 00:33:04, Serial0/0/0
     4.0.0.0/24 is subnetted, 1 subnets
O E2    4.4.4.0 [110/20] via 13.0.0.1, 00:03:33, Serial0/0/0
     10.0.0.0/24 is subnetted, 1 subnets
C       10.234.0.0 is directly connected, FastEthernet0/0
     12.0.0.0/30 is subnetted, 1 subnets
O       12.0.0.0 [110/128] via 13.0.0.1, 00:34:53, Serial0/0/0
     13.0.0.0/30 is subnetted, 1 subnets
C       13.0.0.0 is directly connected, Serial0/0/0
由R3路由表可知，R3要到达R4的环回口只能通过R1，而不能直接到R4。现在我想让R3可以直接到达R4的环回口，而不必通过R1转达。此时只需修改重分布中的管理距离，即把宣告进eigrp协议中的ospf管理距离修成小于110，或者把宣告进ospf协议中的eigrp管理距离修改成大于170（ 对于后面这两句话表述不知道准不准确，如不对，还请大家多多指教）
但是由于同时也要考虑修改管理距离后对R4达到R1环回口的负载均衡没有影响，后来决定采用后一种修改办法 （大家可以试试采用前一种修改办法，此时会有什么不同的效果。我做时到后来是不行的）
修改后R1和R4的路由表显示如下：
R1#show ip route
Gateway of last resort is not set
     1.0.0.0/24 is subnetted, 1 subnets
C       1.1.1.0 is directly connected, Loopback0
     4.0.0.0/24 is subnetted, 1 subnets
O E2    4.4.4.0 [110/20] via 13.0.0.2, 00:03:58, Serial0/0/1
                [110/20] via 12.0.0.2, 00:03:58, Serial0/0/0
     10.0.0.0/24 is subnetted, 1 subnets
O E2    10.234.0.0 [110/20] via 12.0.0.2, 00:34:13, Serial0/0/0
                   [110/20] via 13.0.0.2, 00:34:13, Serial0/0/1
     12.0.0.0/30 is subnetted, 1 subnets
C       12.0.0.0 is directly connected, Serial0/0
     13.0.0.0/30is subnetted, 1 subnets
C       13.0.0.0 is directly connected, Serial0/1
R4#show ip route
Gateway of last resort is not set
     1.0.0.0/24 is subnetted, 1 subnets
D EX    1.1.1.0 [170/307200] via 10.234.0.2, 00:05:34, FastEthernet0/0
                [170/307200] via 10.234.0.3, 00:05:34, FastEthernet0/0     4.0.0.0/24 is subnetted, 1 subnets
C       4.4.4.0 is directly connected, Loopback0
     10.0.0.0/24 is subnetted, 1 subnets
C       10.234.0.0 is directly connected, FastEthernet0/0
     12.0.0.0/30 is subnetted, 1 subnets
D EX    12.0.0.0 [170/307200] via 10.234.0.2, 00:01:45, FastEthernet0/0
                 [170/307200] via 10.234.0.3, 00:00:39, FastEthernet0/0
     13.0.0.0/30 is subnetted, 1 subnets
D EX    13.0.0.0 [170/307200] via 10.234.0.2, 00:01:45, FastEthernet0/0
                 [170/307200] via 10.234.0.3, 00:00:39, FastEthernet0/0
用ping命令测试可通，用至此，完成实验目的。
本实验由于是在packettracer5上搭建的拓扑，在模拟Cisco2811路由器上不能完成修改重分布管理距离的命令，故最后采用在真实机上搭建拓扑并完成实验，结论如上所述。
先附上真实机上操作的配置。
如有不足，请各位多多指教。