ENSP Demo 015.0 GRE

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sys
sys R3

int g0/0/0
ip add 13.0.0.2 30
int g0/0/1
ip add 23.0.0.2 30
int lo 3
ip add 3.3.3.3 32

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sys
sys R1

dhcp enable
ip route-static 0.0.0.0 0 13.0.0.2 

acl 2000
rule 10 permit so 192.168.10.0 0.0.0.255

int g0/0/0
ip add 13.0.0.1 30
nat outbound 2000
int g0/0/1
ip add 192.168.10.254 24
dhcp select interface

int t0/0/0
tunnel-protocol gre
source 13.0.0.1
destination 23.0.0.1
ip add 192.168.20.1 24
keepalive p 1 r 5

ip route-static 172.16.20.0 24 t0/0/0
ip route-static 172.16.10.0 24 t0/0/0

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sys
sys R2

dhcp enable
ip route-static 0.0.0.0 0 23.0.0.2 

acl 2000
rule 10 permit so 172.16.0.0 0.0.0.255

int g0/0/0
ip add 23.0.0.1 30
nat outbound 2000
int g0/0/1
ip add 172.16.0.254 24
dhcp select interface

int t0/0/0
tunnel-protocol gre
source 23.0.0.1
destination 13.0.0.1
ip add 172.16.20.1 24
keepalive p 1 r 5

ip route-static 192.168.20.0 24 t0/0/0
ip route-static 192.168.10.0 24 t0/0/0

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keepalive p 1 r 5用于隧道检测，检测间隔1s，超过5s无响应接口down掉

GRE隧道两端IP地址不是同一网段，所以需要添加静态路由

GRE可以封装组播，所以也可以选择OSPF、RIPv2代替静态路由

ip route-static 172.16.20.0 24 t0/0/0
ip route-static 172.16.10.0 24 t0/0/0
R1可以将静态路由替换为OSPF
ospf 1 router-id 1.1.1.1
a 0
net 192.168.10.0 0.0.0.255
net 192.168.20.0 0.0.0.255

ip route-static 192.168.20.0 24 t0/0/0
ip route-static 192.168.10.0 24 t0/0/0
R2可以将静态路由替换为OSPF
ospf 1 router-id 2.2.2.2
a 0
net 172.16.0.0 0.0.0.255
net 172.16.20.0 0.0.0.255