GRE（Generic Routing Encapsulation 通用路由协议）提供了一种协议的报文封装在另一个协议报文中的机制，使报文能够在异咱网络（如IPv4网络）中传输，而异咱报文传输的通道称为tunnel。
GRE协议也可以做为VPN的第三层隧道（tunnel）协议，为VPN数据提供透明传输通道，Tunnel是一个虚拟的点对点连接，可以看成仅支持点对点连接的虚拟接口，这个接口提供一条通路，使封装的数据报能够这个通路上传输，并在一个Tunnel的两端分别在对数据报进行封装及解封装。
AR2配置默认路由
ip route-static 0.0.0.0 0 12.1.1.2
AR3配置默认路由
ip route-static 0.0.0.0 0 10.1.23.2
PC1测试与server1的连通性
可以观察到跨越了公网的两个私网网段之间默认是无法直接通信的，此时可以通过GRE协议来实现通信
配置GRE
在路由器R2和R3上配置GRE tunnel
R2配置
interface Serial1/0/0 link-protocol ppp ip address 10.1.12.1 255.255.255.0 interface GigabitEthernet0/0/0 ip address 192.168.10.254 255.255.255.0 interface Tunnel0/0/0 ip address 172.16.1.1 255.255.255.0 tunnel-protocol gre source 10.1.12.1 destination 10.1.23.3 # ip route-static 0.0.0.0 0.0.0.0 10.1.12.2
R3配置
interface Serial1/0/1 link-protocol ppp ip address 10.1.23.3 255.255.255.0 interface GigabitEthernet0/0/0 ip address 192.168.20.254 255.255.255.0 interface Tunnel0/0/0 ip address 172.16.1.2 255.255.255.0 tunnel-protocol gre source 10.1.23.3 destination 10.1.12.1 ip route-static 0.0.0.0 0.0.0.0 10.1.23.2
R1配置
interface Serial1/0/0 link-protocol ppp ip address 10.1.12.2 255.255.255.0 # interface Serial1/0/1 link-protocol ppp ip address 10.1.23.2 255.255.255.0
[R2]dis interface Tunnel 0/0/0 Tunnel0/0/0 current state : UP Line protocol current state : UP Last line protocol up time : 2020-06-03 10:46:00 UTC-08:00 Description:HUAWEI, AR Series, Tunnel0/0/0 Interface Route Port,The Maximum Transmit Unit is 1500 Internet Address is 172.16.1.1/24 Encapsulation is TUNNEL, loopback not set Tunnel source 10.1.12.1 (Serial1/0/0), destination 10.1.23.3 Tunnel protocol/transport GRE/IP, key disabled keepalive disabled Checksumming of packets disabled Current system time: 2020-06-03 10:49:19-08:00 300 seconds input rate 0 bits/sec, 0 packets/sec 300 seconds output rate 8 bits/sec, 0 packets/sec 0 seconds input rate 0 bits/sec, 0 packets/sec 0 seconds output rate 0 bits/sec, 0 packets/sec 0 packets input, 0 bytes 0 input error 5 packets output, 540 bytes 0 output error Input bandwidth utilization : -- Output bandwidth utilization : --
[R3]dis interface Tunnel 0/0/0 Tunnel0/0/0 current state : UP Line protocol current state : UP Last line protocol up time : 2020-06-03 10:36:58 UTC-08:00 Description:HUAWEI, AR Series, Tunnel0/0/0 Interface Route Port,The Maximum Transmit Unit is 1500 Internet Address is 172.16.1.2/24 Encapsulation is TUNNEL, loopback not set Tunnel source 10.1.23.3 (Serial1/0/1), destination 10.1.12.1 Tunnel protocol/transport GRE/IP, key disabled keepalive disabled Checksumming of packets disabled Current system time: 2020-06-03 10:49:45-08:00 300 seconds input rate 0 bits/sec, 0 packets/sec 300 seconds output rate 0 bits/sec, 0 packets/sec 0 seconds input rate 0 bits/sec, 0 packets/sec 0 seconds output rate 0 bits/sec, 0 packets/sec 0 packets input, 0 bytes 0 input error 5 packets output, 540 bytes 0 output error Input bandwidth utilization : -- Output bandwidth utilization : --
[R2]dis ip routing-table Route Flags: R - relay, D - download to fib ------------------------------------------------------------------------------ Routing Tables: Public Destinations : 15 Routes : 15 Destination/Mask Proto Pre Cost Flags NextHop Interface 0.0.0.0/0 Static 60 0 RD 10.1.12.2 Serial1/0/0 10.1.12.0/24 Direct 0 0 D 10.1.12.1 Serial1/0/0 10.1.12.1/32 Direct 0 0 D 127.0.0.1 Serial1/0/0 10.1.12.2/32 Direct 0 0 D 10.1.12.2 Serial1/0/0 10.1.12.255/32 Direct 0 0 D 127.0.0.1 Serial1/0/0 127.0.0.0/8 Direct 0 0 D 127.0.0.1 InLoopBack0 127.0.0.1/32 Direct 0 0 D 127.0.0.1 InLoopBack0 127.255.255.255/32 Direct 0 0 D 127.0.0.1 InLoopBack0 172.16.1.0/24 Direct 0 0 D 172.16.1.1 Tunnel0/0/0 172.16.1.1/32 Direct 0 0 D 127.0.0.1 Tunnel0/0/0 172.16.1.255/32 Direct 0 0 D 127.0.0.1 Tunnel0/0/0 192.168.10.0/24 Direct 0 0 D 192.168.10.254 GigabitEthernet 0/0/0 192.168.10.254/32 Direct 0 0 D 127.0.0.1 GigabitEthernet 0/0/0 192.168.10.255/32 Direct 0 0 D 127.0.0.1 GigabitEthernet 0/0/0 255.255.255.255/32 Direct 0 0 D 127.0.0.1 InLoopBack0
可能观察到R2和R3的路由表中已经有所配置隧道接口的路由条目，即R2和R3之间已经形成了类似点到点直连的逻辑链路，但是没有互相接收到对方的私网络信息
配置基于GRE接口的动态路由协议
还是连通不了
R2上配置
ospf 1 router-id 2.2.2.2 area 0.0.0.0 network 172.16.1.0 0.0.0.255 network 192.168.10.0 0.0.0.255
R3配置
ospf 1 router-id 3.3.3.3 area 0.0.0.0 network 172.16.1.0 0.0.0.255 network 192.168.20.0 0.0.0.255
[R2]dis ip routing-table p o Route Flags: R - relay, D - download to fib ------------------------------------------------------------------------------ Public routing table : OSPF Destinations : 1 Routes : 1 OSPF routing table status : <Active> Destinations : 1 Routes : 1 Destination/Mask Proto Pre Cost Flags NextHop Interface 192.168.20.0/24 OSPF 10 1563 D 172.16.1.2 Tunnel0/0/0 OSPF routing table status : <Inactive> Destinations : 0 Routes : 0
[R3]dis ip routing-table p os Route Flags: R - relay, D - download to fib ------------------------------------------------------------------------------ Public routing table : OSPF Destinations : 1 Routes : 1 OSPF routing table status : <Active> Destinations : 1 Routes : 1 Destination/Mask Proto Pre Cost Flags NextHop Interface 192.168.10.0/24 OSPF 10 1563 D 172.16.1.1 Tunnel0/0/0 OSPF routing table status : <Inactive> Destinations : 0 Routes : 0
测试
