一、拓扑搭建（R1和R6连两根线是因为每个GRE分别占用一个接口）
二、配置地址
【R1】
[r1-GigabitEthernet0/0/0]ip address 16.0.0.1 24
[r1-GigabitEthernet0/0/1]ip address 116.0.0.1 24
[r1-LoopBack0]ip address 192.168.1.1 24
【R2】
[r2-GigabitEthernet0/0/0]ip address 26.0.0.1 24
[r2-LoopBack0]ip address 192.168.2.1 24
【R3】
[r3-GigabitEthernet0/0/0]ip address 36.0.0.1 24
[r3-LoopBack0]ip address 192.168.3.1 24
【R4】
[r4-GigabitEthernet0/0/0]ip address 46.0.0.1 24
[r4-LoopBack0]ip address 192.168.4.1 24
【R5】
[r5-GigabitEthernet0/0/0]ip address 56.0.0.1 24
[r5-LoopBack0]ip address 192.168.5.1 24
【R6】
[ISP-GigabitEthernet2/0/0]ip address 116.0.0.2 24
[ISP-GigabitEthernet0/0/0]ip address 16.0.0.2 24
[ISP-GigabitEthernet0/0/1]ip address 26.0.0.2 24
[ISP-GigabitEthernet0/0/2]ip address 36.0.0.2 24
[ISP-GigabitEthernet3/0/0]ip address 46.0.0.2 24
[ISP-GigabitEthernet4/0/0]ip address 56.0.0.2 24
三、配缺省
[r1]ip route-static 0.0.0.0 0 116.0.0.2
[r1]ip route-static 0.0.0.0 0 16.0.0.2
[r2]ip route-static 0.0.0.0 0 26.0.0.2
[r3]ip route-static 0.0.0.0 0 36.0.0.2
[r4]ip route-static 0.0.0.0 0 46.0.0.2
[r5]ip route-static 0.0.0.0 0 56.0.0.2
四、R1/R4/R5为全连的MGRE结构
分析：三部路由每台分别都是另外两台的中心
将R1/R4/R5组合在一起的网段设为192.168.6.0/24，同时将16.0.0.1的接口作为本次的全连MGRE
[r1]interface t0/0/0
[r1-Tunnel0/0/0]ip address 192.168.6.1 24
[r1-Tunnel0/0/0]tunnel-protocol gre p2mp
[r1-Tunnel0/0/0]source 16.0.0.1
[r1-Tunnel0/0/0]nhrp network-id 100
[r1-Tunnel0/0/0]nhrp entry multicast dynamic
[r4]interface t0/0/0
[r4-Tunnel0/0/0]ip address 192.168.6.2 24
[r4-Tunnel0/0/0]tunnel-protocol gre p2mp
[r4-Tunnel0/0/0]source 46.0.0.1
[r4-Tunnel0/0/0]nhrp network-id 100
[r4-Tunnel0/0/0]nhrp entry multicast dynamic
[r5]interface t0/0/0
[r5-Tunnel0/0/0]ip address 192.168.6.3 24
[r5-Tunnel0/0/0]tunnel-protocol gre p2mp
[r5-Tunnel0/0/0]source 56.0.0.1
[r5-Tunnel0/0/0]nhrp network-id 100
[r5-Tunnel0/0/0]nhrp entry multicast dynamic
这样R1/4/5就都在nhrp为100中作为中心了，所以接下来需要相互认证
[r1-Tunnel0/0/0]nhrp entry 192.168.6.2 46.0.0.1 register
[r1-Tunnel0/0/0]nhrp entry 192.168.6.3 56.0.0.1 register
[r4-Tunnel0/0/0]nhrp entry 192.168.6.3 56.0.0.1 register
（[r4-Tunnel0/0/0]nhrp entry 192.168.6.1 16.0.0.1 registe）可敲可不敲，R1认证后R4不敲也可以
（[r5-Tunnel0/0/0]nhrp entry 192.168.6.1 16.0.0.1 register
[r5-Tunnel0/0/0]nhrp entry 192.168.6.2 46.0.0.1 register）
五、R1/R2/R3为星型拓扑，R1为中心站点
分析：三台路由器以R1为中心站点
将R1/R2/R3组合在一起的网段设为192.168.7.0/24，同时将116.0.0.1的接口作为本次的MGRE
[r1]interface t0/0/1
[r1-Tunnel0/0/1]ip address 192.168.7.1 24
[r1-Tunnel0/0/1]tunnel-protocol gre p2mp
[r1-Tunnel0/0/1]source 116.0.0.1
[r1-Tunnel0/0/1]nhrp network-id 110
[r1-Tunnel0/0/1]nhrp entry multicast dynamic
[r2]interface t0/0/1
[r2-Tunnel0/0/1]ip address 192.168.7.2 24
[r2-Tunnel0/0/1]tunnel-protocol gre p2mp
[r2-Tunnel0/0/2]source GigabitEthernet 0/0/0（出接口）
[r2-Tunnel0/0/1]nhrp network-id 110
[r2-Tunnel0/0/1]nhrp entry 192.168.7.1 116.0.0.1 register （中心站点）
[r3]interface t0/0/1
[r3-Tunnel0/0/1]ip address 192.168.7.3 24
[r3-Tunnel0/0/1]tunnel-protocol gre p2mp
[r3-Tunnel0/0/2]source GigabitEthernet 0/0/0（出接口）
[r3-Tunnel0/0/1]nhrp network-id 110
[r3-Tunnel0/0/1]nhrp entry 192.168.7.1 116.0.0.1 register （中心站点）
六、使用OSPF完成所有私有网段相互通讯
[r1]ospf 1 router-id 1.1.1.1
[r1-ospf-1]area 0
[r1-ospf-1-area-0.0.0.0]network 192.168.1.0 0.0.0.255
[r1-ospf-1-area-0.0.0.0]network 192.168.6.0 0.0.0.255
[r1-ospf-1-area-0.0.0.0]network 192.168.7.0 0.0.0.255
[r2]ospf 1 router-id 2.2.2.2
[r2-ospf-1]area 0
[r2-ospf-1-area-0.0.0.0]network 192.168.2.0 0.0.0.255
[r2-ospf-1-area-0.0.0.0]network 192.168.7.0 0.0.0.255
[r3]ospf 1 router-id 3.3.3.3
[r3-ospf-1]area 0
[r3-ospf-1-area-0.0.0.0]network 192.168.3.0 0.0.0.255
[r3-ospf-1-area-0.0.0.0]network 192.168.7.0 0.0.0.255
[r4]ospf 1 router-id 4.4.4.4
[r4-ospf-1]area 0
[r4-ospf-1-area-0.0.0.0]network 192.168.4.0 0.0.0.255
[r4-ospf-1-area-0.0.0.0]network 192.168.6.0 0.0.0.255
[r5]ospf 1 router-id 5.5.5.5
[r5-ospf-1]area 0
[r5-ospf-1-area-0.0.0.0]network 192.168.5.0 0.0.0.255
[r5-ospf-1-area-0.0.0.0]network 192.168.6.0 0.0.0.255
问题一：在R1/R4/R5中，R1只和R4或R5（只能选一个）建立了邻居关系
问题二： 在R1/R2/R3中，R1只和R2或R3（只能选一个）建立了邻居关系
原因：是由于Tunnel口在OSPF的工作模式导致的——Tunnel口在GRE的默认类型是P2P（点到点网络）类型，只能建立一个邻居关系
解决一：改变类型为broadcast（但对于R1/R2/R3之间的GRE需要选举DR）
解决二：改变类型为P2MP（不需要选举）
解决一：
（1）R1/R4/R5的全连MGRE的修改
[r1]interface t0/0/0
[r1-Tunnel0/0/0]ospf network-type broadcast
[r4]interface t00/0/0
[r4-Tunnel0/0/0]ospf network-type broadcast
[r5]interface t00/0/0
[r5-Tunnel0/0/0]ospf network-type broadcast
（2）R1/R2/R3的GRE修改
必须选举R1为DR，将R1的优先级改大或让R2/R3放弃选举（这里用了方法一）
[r1]interface t00/0/1
[r1-Tunnel0/0/1]ospf network-type broadcast
[r1-Tunnel0/0/1]ospf dr-priority 10（同时重启三台的ospf进程，因为ospf有非抢占性）
[r2]interface t00/0/1
[r2-Tunnel0/0/1]ospf network-type broadcast
[r3]interface t00/0/1
[r3-Tunnel0/0/1]ospf network-type broadcast
解决二：
[r1]interface t00/0/1
[r1-Tunnel0/0/1]ospf network-type P2MP
[r2]interface t00/0/1
[r2-Tunnel0/0/1]ospf network-type P2MP
[r3]interface t00/0/1
[r3-Tunnel0/0/1]ospf network-type P2MP