1. Topology setup (R1 and R6 are connected by two lines because each GRE occupies one interface)
2. Configure address
[ 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
4. R1/R4/R5 are fully connected MGRE structure
Analysis: Each of the three routers belongs to the other two. Center
Set the network segment of R1/R4/R5 to 192.168.6.0/24, and use the interface of 16.0.0.1 as this time Quanlian 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
In this way, R1/4/5 are all centered in nhrp of 100, so mutual authentication is required next.
[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 register) You can knock it or not. After R1 authentication, you can also knock R4 without it
（[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）
5. R1/R2/R3 is a star topology, and R1 is the central site
Analysis: Three routers with R1 as the central site
The network segment of R1/R2/R3 is set to 192.168.7.0/24, and the interface of 116.0.0.1 is used as this 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）
6. Use OSPF to complete mutual communication between all private network segments
[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
Question 1: In R1/R4/R5, R1 only has a neighbor relationship with R4 or R5 (you can only choose one)
Question 2: In R1/R2/R3 , R1 has only established a neighbor relationship with R2 or R3 (you can only choose one)
Reason: This is due to the working mode of the tunnel port in OSPF - the default type of the tunnel port in GRE is P2P (point-to-point network) type, only one neighbor relationship can be established
Solution 1: Change the type to broadcast (but for GRE between R1/R2/R3, DR needs to be elected)
Solution 2: Change the type to P2MP (no election required)
Solution 1:
(1) Modification of fully connected MGRE of R1/R4/R5
[r1]interface t0/0/0< /span>
[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) GRE modification of R1/R2/R3
R1 must be elected as DR, increase the priority of R1 or let R2/R3 give up the election (the method used here is 1)
[r1]interface t00/0/1
[r1-Tunnel0/0/1]ospf network-type broadcast
[r1-Tunnel0 /0/1]ospf dr-priority 10(Restart the three ospf processes at the same time, because ospf is non-preemptive)
[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