Hello everyone, in this LAB I will configure GRE Tunnels with following topology.

R1
#INTERFACE CONFIGURATION
R1#conf t
R1(config)#int e0/0
R1(config-if)#ip addr 10.0.1.1 255.255.255.0
R1(config-if)#no sh
R1(config-if)#int e0/1
R1(config-if)#ip addr 1.1.1.2 255.255.255.252
R1(config-if)#no sh
R1(config-if)#exit
#OSPF
R1(config)#router ospf 1
R1(config-router)#network 1.1.1.0 0.0.0.3 area 0
R1(config-router)#network 10.0.1.0 0.0.0.255 area 0
R1(config-router)#exitR2
#INTERFACE CONFIGURATION
R2#conf t
R2(config)#int e0/0
R2(config-if)#ip addr 10.0.2.1 255.255.255.0
R2(config-if)#no sh
R2(config-if)#int e0/2
R2(config-if)#ip addr 1.1.2.2 255.255.255.252
R2(config-if)#no sh
R2(config-if)#exit
#OSPF
R2(config)#router ospf 1
R2(config-router)#network 10.0.2.0 0.0.0.255 area 0
R2(config-router)#network 1.1.2.0 0.0.0.3 area 0
R2(config-router)#exitR3
#VRF DEFINITION
R3#conf t
R3(config)#ip vrf Customer-A
R3(config-vrf)#exit
R3(config)#ip vrf Customer-B
R3(config-vrf)#exit
#IMPLEMENT VRF UNDER INTERFACES
R3(config)#int e0/1
R3(config-if)#ip vrf forwarding Customer-A
R3(config-if)#ip addr 1.1.1.1 255.255.255.252
R3(config-if)#no sh
R3(config-if)#int e0/0
R3(config-if)#ip vrf forwarding Customer-A
R3(config-if)#ip addr 1.1.5.1 255.255.255.252
R3(config-if)#no sh
R3(config-if)#exit
R3(config)#int e0/2
R3(config-if)#ip vrf forwarding Customer-B
R3(config-if)#ip addr 1.1.2.1 255.255.255.252
R3(config-if)#no sh
R3(config-if)#int e0/3
R3(config-if)#ip vrf forwarding Customer-B
R3(config-if)#ip addr 1.1.6.1 255.255.255.252
R3(config-if)#no sh
R3(config-if)#exit
#OSPF
R3(config)#router ospf 1 vrf Customer-A
R3(config-router)#network 1.1.1.0 0.0.0.3 area 0
R3(config-router)#network 1.1.5.0 0.0.0.3 area 0
R3(config-router)#capability vrf-lite
R3(config-router)#exit
R3(config)#router ospf 2 vrf Customer-B
R3(config-router)#network 1.1.2.0 0.0.0.3 area 0
R3(config-router)#network 1.1.6.0 0.0.0.3 area 0
R3(config-router)#capability vrf-lite
R3(config-router)#exitR4
#VRF DEFINITION
R4#conf t
R4(config)#ip vrf Customer-A
R4(config-vrf)#exit
#IMPLEMENT VRF UNDER INTERFACES
R4(config-if)#int e0/0
R4(config-if)#ip vrf forwarding Customer-A
R4(config-if)#ip addr 1.1.5.2 255.255.255.252
R4(config-if)#no sh
R4(config-if)#int e0/1
R4(config-if)#ip vrf forwarding Customer-A
R4(config-if)#ip addr 1.1.7.1 255.255.255.252
R4(config-if)#no sh
R4(config-if)#exit
#OSPF
R4(config)#router ospf 1 vrf Customer-A
R4(config-router)#network 1.1.5.0 0.0.0.3 area 0
R4(config-router)#network 1.1.7.0 0.0.0.3 area 0
R4(config-router)#capability vrf-lite
R4(config-router)#exitR5
#VRF DEFINITION
R5#conf t
R5(config)#ip vrf Customer-B
R5(config-vrf)#exit
#IMPLEMENT VRF UNDER INTERFACES
R5(config)#int e0/3
R5(config-if)#ip vrf forwarding Customer-B
R5(config-if)#ip addr 1.1.6.2 255.255.255.252
R5(config-if)#no sh
R5(config-if)#int e0/1
R5(config-if)#ip vrf forwarding Customer-B
R5(config-if)#ip addr 1.1.8.1 255.255.255.252
R5(config-if)#no sh
R5(config-if)#exit
#OSPF
R5(config)#router ospf 1 vrf Customer-B
R5(config-router)#network 1.1.6.0 0.0.0.3 area 0
R5(config-router)#network 1.1.8.0 0.0.0.3 area 0
R5(config-router)#capability vrf-lite
R5(config-router)#exitR6
#VRF DEFINITION
R6#conf t
R6(config)#ip vrf Customer-A
R6(config-vrf)#exit
#IMPLEMENT VRF UNDER INTERFACES
R6(config)#int e0/1
R6(config-if)#ip vrf forwarding Customer-A
R6(config-if)#ip addr 1.1.7.2 255.255.255.252
R6(config-if)#no sh
R6(config-if)#int e0/0
R6(config-if)#ip vrf forwarding Customer-A
R6(config-if)#ip addr 1.1.9.1 255.255.255.252
R6(config-if)#no sh
R6(config-if)#exit
#OSPF
R6(config)#router ospf 1 vrf Customer-A
R6(config-router)#network 1.1.7.0 0.0.0.3 area 0
R6(config-router)#network 1.1.9.0 0.0.0.3 area 0
R6(config-router)#capability vrf-lite
R6(config-router)#exitR7
#VRF DEFINITION
R7#conf t
R7(config)#ip vrf Customer-B
R7(config-vrf)#exit
#IMPLEMENT VRF UNDER INTERFACES
R7(config)#int e0/1
R7(config-if)#ip vrf forwarding Customer-B
R7(config-if)#ip addr 1.1.8.2 255.255.255.252
R7(config-if)#no sh
R7(config-if)#int e0/3
R7(config-if)#ip vrf forwarding Customer-B
R7(config-if)#ip addr 1.1.10.1 255.255.255.252
R7(config-if)#no sh
R7(config-if)#exit
#OSPF
R7(config)#router ospf 1 vrf Customer-B
R7(config-router)#network 1.1.8.0 0.0.0.3 area 0
R7(config-router)#network 1.1.10.0 0.0.0.3 area 0
R7(config-router)#capability vrf-lite
R7(config-router)#exitR8
#VRF DEFINITION
R8#conf t
R8(config)#ip vrf Customer-A
R8(config-vrf)#exit
R8(config)#ip vrf Customer-B
R8(config-vrf)#exit
R8(config)#int e0/0
R8(config-if)#ip vrf forwarding Customer-A
R8(config-if)#ip addr 1.1.9.2 255.255.255.252
R8(config-if)#no sh
R8(config-if)#int e0/2
R8(config-if)#ip vrf forwarding Customer-A
R8(config-if)#ip addr 1.1.4.1 255.255.255.252
R8(config-if)#int e0/3
R8(config-if)#ip vrf forwarding Customer-B
R8(config-if)#ip addr 1.1.10.2 255.255.255.252
R8(config-if)#no sh
R8(config-if)#int e0/1
R8(config-if)#ip vrf forwarding Customer-B
R8(config-if)#ip addr 1.1.3.1 255.255.255.252
R8(config-if)#no sh
R8(config-if)#exit
#OSPF
R8(config)#router ospf 1 vrf Customer-A
R8(config-router)#network 1.1.9.0 0.0.0.3 area 0
R8(config-router)#network 1.1.4.0 0.0.0.3 area 0
R8(config-router)#capability vrf-lite
R8(config-router)#exit
R8(config)#router ospf 2 vrf Customer-B
R8(config-router)#network 1.1.10.0 0.0.0.3 area 0
R8(config-router)#network 1.1.3.0 0.0.0.3 area 0
R8(config-router)#capability vrf-lite
R8(config-router)#exitR9
#INTERFACE CONFIGURATION
R9#conf t
R9(config)#int e0/0
R9(config-if)#ip addr 10.0.3.1 255.255.255.0
R9(config-if)#no sh
R9(config-if)#int e0/1
R9(config-if)#ip addr 1.1.3.2 255.255.255.252
R9(config-if)#no sh
R9(config-if)#exit
#OSPF
R9(config)#router ospf 1
R9(config-router)#network 10.0.3.0 0.0.0.255 area 0
R9(config-router)#network 1.1.3.0 0.0.0.3 area 0
R9(config-router)#exitR10
#INTERFACE CONFIGURATION
R10#conf t
R10(config)#int e0/0
R10(config-if)#ip addr 10.0.4.1 255.255.255.0
R10(config-if)#no sh
R10(config-if)#int e0/2
R10(config-if)#ip addr 1.1.4.2 255.255.255.252
R10(config-if)#no sh
R10(config-if)#exit
#OSPF
R10(config)#router ospf 1
R10(config-router)#network 10.0.4.0 0.0.0.255 area 0
R10(config-router)#network 1.1.4.0 0.0.0.3 area 0
R10(config-router)#exitVPC15
VPCS> ip 10.0.1.10 255.255.255.0 gateway 10.0.1.1
Checking for duplicate address...
VPCS : 10.0.1.10 255.255.255.0 gateway 10.0.1.VPC18
VPCS> ip 10.0.2.10 255.255.255.0 gateway 10.0.2.1
Checking for duplicate address...
VPCS : 10.0.2.10 255.255.255.0 gateway 10.0.2.1VPC19
VPCS> ip 10.0.3.10 255.255.255.0 gateway 10.0.3.1
Checking for duplicate address...
VPCS : 10.0.3.10 255.255.255.0 gateway 10.0.3.1VPC21
VPCS> ip 10.0.4.10 255.255.255.0 gateway 10.0.4.1
Checking for duplicate address...
VPCS : 10.0.4.10 255.255.255.0 gateway 10.0.4.1Test
VPC21 to VPC15
VPCS> ping 10.0.1.10
84 bytes from 10.0.1.10 icmp_seq=1 ttl=58 time=2.750 ms
84 bytes from 10.0.1.10 icmp_seq=2 ttl=58 time=1.582 ms
84 bytes from 10.0.1.10 icmp_seq=3 ttl=58 time=2.427 ms
84 bytes from 10.0.1.10 icmp_seq=4 ttl=58 time=2.167 ms
84 bytes from 10.0.1.10 icmp_seq=5 ttl=58 time=1.760 msVPC18 to VPC19
VPCS> ping 10.0.3.10
84 bytes from 10.0.3.10 icmp_seq=1 ttl=58 time=2.183 ms
84 bytes from 10.0.3.10 icmp_seq=2 ttl=58 time=2.037 ms
84 bytes from 10.0.3.10 icmp_seq=3 ttl=58 time=2.224 ms
84 bytes from 10.0.3.10 icmp_seq=4 ttl=58 time=1.949 ms
84 bytes from 10.0.3.10 icmp_seq=5 ttl=58 time=2.328 msThank you for taking the time to read this article.
Keep up the good work!