How to Configure a GRE/IPsec VPN

Router1#sho run
Building configuration...

Current configuration : 1015 bytes
!
version 12.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname Router1
!
boot-start-marker
boot-end-marker
!
no logging console
enable secret 5 $1$uL3z$2QfdCX4Vot.YovoIP0pQA/
!
no aaa new-model
!
resource policy
!
memory-size iomem 5
ip subnet-zero
!
ip cef
!
interface Serial0/0
description ********CONNECTION TO ISP**********
ip address 12.34.56.2 255.255.255.252
serial restart-delay 0
!
interface Serial0/1
no ip address
shutdown
serial restart-delay 0
!
interface Serial0/2
no ip address
shutdown
serial restart-delay 0
!
interface Serial0/3
no ip address
shutdown
serial restart-delay 0
!
interface FastEthernet1/0
ip address 192.168.1.1 255.255.255.0
duplex auto
speed auto
!
ip http server
no ip http secure-server
!
ip classless
ip route 0.0.0.0 0.0.0.0 12.34.56.1
!
control-plane
!
line con 0
line aux 0
line vty 0 4
password cisco
login
!
!
end
Router1#

*********************************************************************************************************************************************************************************************
ISP#sho run
Building configuration...

Current configuration : 916 bytes
!
version 12.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname ISP
!
boot-start-marker
boot-end-marker
!
no aaa new-model
!
resource policy
!
memory-size iomem 5
ip subnet-zero
!
ip cef
!
interface Serial0/0
description *******CONNECTION TO R1********
ip address 12.34.56.1 255.255.255.252
serial restart-delay 0
!
interface Serial0/1
description *******CONNECTION TO R2*********
ip address 23.45.67.1 255.255.255.252
serial restart-delay 0
!
interface Serial0/2
description *********CONNECTION TO R3************
ip address 34.56.78.1 255.255.255.252
serial restart-delay 0
!
interface Serial0/3
no ip address
shutdown
serial restart-delay 0
!
ip http server
no ip http secure-server
!
ip classless
!
control-plane
!
!
line con 0
line aux 0
line vty 0 4
!
!
end

ISP#
*********************************************************************************************************************************************************************************************

Router2#sho run
Building configuration...

Current configuration : 993 bytes
!
version 12.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname Router2
!
boot-start-marker
boot-end-marker
!
enable secret 5 $1$rz8E$xI0ZPwpwL1BkZlOiRAnlK/
!
no aaa new-model
!
resource policy
!
memory-size iomem 5
ip subnet-zero
!
!
ip cef
!
interface Serial0/0
description ******CONNECTION TO ISP*********
ip address 23.45.67.2 255.255.255.252
serial restart-delay 0
!
interface Serial0/1
no ip address
shutdown
serial restart-delay 0
!
interface Serial0/2
no ip address
shutdown
serial restart-delay 0
!
interface Serial0/3
no ip address
shutdown
serial restart-delay 0
!
interface FastEthernet1/0
ip address 192.168.2.1 255.255.255.0
duplex auto
speed auto
!
ip http server
no ip http secure-server
!
ip classless
ip route 0.0.0.0 0.0.0.0 23.45.67.1
!
control-plane
!
line con 0
line aux 0
line vty 0 4
password cisco
login
!
!
end

Router2#
*********************************************************************************************************************************************************************************************

Router3#sho run
Building configuration...

Current configuration : 1009 bytes
!
version 12.4
service timestamps debug datetime msec
service timestamps log datetime msec
no service password-encryption
!
hostname Router3
!
boot-start-marker
boot-end-marker
!
no logging console
enable secret 5 $1$ZGoM$cD/Py.DpH/4qW7muT8nrW0
!
no aaa new-model
!
resource policy
!
memory-size iomem 5
ip subnet-zero
!
ip cef
!
interface Serial0/0
description *****CONNECTION TO ISP*******
ip address 34.56.78.2 255.255.255.252
serial restart-delay 0
!
interface Serial0/1
no ip address
shutdown
serial restart-delay 0
!
interface Serial0/2
no ip address
shutdown
serial restart-delay 0
!
interface Serial0/3
no ip address
shutdown
serial restart-delay 0
!
interface FastEthernet1/0
ip address 192.168.3.1 255.255.255.0
duplex auto
speed auto
!
ip http server
no ip http secure-server
!
ip classless
ip route 0.0.0.0 0.0.0.0 34.56.78.1
!
!
!
!
control-plane
!
line con 0
line aux 0
line vty 0 4
password cisco
login
!
!
end

Router3#
*********************************************************************************************************************************************************************************************

IPSEC tunnel between R1 and R2 and R3

This configuration is about how to configure GRE with IPSEC. GRE can be used to transmit routing protocols over the internet, it acts as if the link is a point to point circuit.

Create a tunnel interface on R1 which will communicate with R2






Setting Up the Tunnel.
Tunnel Source IP address will be the IP address of the Serial interface on the outside of ( Router1 )
Tunnel Destination will be the IP address of R2 Serial interface connecting to the internet ( 23.45.67.2 )

Create Another Tunnel to Router R3
Create another Tunnel source fron R1 (12.34.56.2 ) to R3 The Tunnel Source will be the WAN IP of Router 1
Create another Tunnel Destination to R3 ( 34.56.78.2 ) The Tunnel Destination will also be the WAN IP of R3

And then on Router 1 configure Eigrp to R2 and R3
Once the Eigrp instance has been configured
We now need to configure the Networks that we want to advertise

The first Network will be the LAN IP
The Second Network will be Tunnel IP from Router 1 to Router 2
The Third Network will be the Tunnel IP from Router 1 to Router 3


interface tunnel 0
description GRE Tunnel To Router 2
ip address 192.168.200.1 255.255.255.0
tunnel source 12.34.56.2
tunnel destination 23.45.67.2

interface tunnel 2
Description Tunnel To Router R3
ip address 192.168.201.1 255.255.255.0
tunnel source 12.34.56.2
tunnel destination 34.56.78.2

router eigrp 100
no auto summary
network 192.168.1.0
network 192.168.200.0
network 192.168.201.0

Before Tunnels are established..

Router1#sho ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route

Gateway of last resort is 12.34.56.1 to network 0.0.0.0

C 192.168.200.0/24 is directly connected, Tunnel0
C 192.168.201.0/24 is directly connected, Tunnel2
12.0.0.0/30 is subnetted, 1 subnets
C 12.34.56.0 is directly connected, Serial0/0
C 192.168.1.0/24 is directly connected, FastEthernet1/0
S* 0.0.0.0/0 [1/0] via 12.34.56.1
Router1#

**************************************************************************************
Sho ip route state after Tunnels is established
**************************************************************************************

Router1#sho ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route

Gateway of last resort is 12.34.56.1 to network 0.0.0.0

C 192.168.200.0/24 is directly connected, Tunnel0
C 192.168.201.0/24 is directly connected, Tunnel2
12.0.0.0/30 is subnetted, 1 subnets
C 12.34.56.0 is directly connected, Serial0/0
C 192.168.1.0/24 is directly connected, FastEthernet1/0
D 192.168.2.0/24 [90/297246976] via 192.168.200.2, 00:02:51, Tunnel0
S* 0.0.0.0/0 [1/0] via 12.34.56.1
Router1#




*************************************************************************************
Now we need to connect to Router R2 and configure R2 as shown Below:
**************************************************************************************

R2
interface tunnel 0
description GRE Tunnel To Router 1
ip address 192.168.200.2 255.255.255.0
tunnel source 23.45.67.2
tunnel destination 12.34.56.2
exit

router eigrp 100
no auto summary
network 192.168.2.0
network 192.168.200.0


Router2#sho ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route

Gateway of last resort is 23.45.67.1 to network 0.0.0.0

23.0.0.0/30 is subnetted, 1 subnets
C 23.45.67.0 is directly connected, Serial0/0
C 192.168.2.0/24 is directly connected, FastEthernet1/0
S* 0.0.0.0/0 [1/0] via 23.45.67.1
Router2#

*****************************************************************************************************
Show ip route state after Tunnels are established
*****************************************************************************************************

Router2#sho ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route

Gateway of last resort is 23.45.67.1 to network 0.0.0.0

23.0.0.0/30 is subnetted, 1 subnets
C 23.45.67.0 is directly connected, Serial0/0
C 192.168.200.0/24 is directly connected, Tunnel0
D 192.168.201.0/24 [90/310044416] via 192.168.200.1, 00:00:15, Tunnel0
D 192.168.1.0/24 [90/297246976] via 192.168.200.1, 00:00:15, Tunnel0
C 192.168.2.0/24 is directly connected, FastEthernet1/0
S* 0.0.0.0/0 [1/0] via 23.45.67.1
Router2#


****************************************************************************************
Now we need to connect to Router R2 and configure R2 as shown Below
****************************************************************************************

R3
interface tunnel 0
description GRE Tunnel To Router 1
ip address 192.168.201.2 255.255.255.0
tunnel source 34.56.78.2
tunnel destination 12.34.56.2
exit

router eigrp 100
no auto summary
network 192.168.3.0
network 192.168.201.0


****************************************************************************************
Show ip route state on R3 before Tunnel is established.
****************************************************************************************



Router3#sho ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route

Gateway of last resort is 34.56.78.1 to network 0.0.0.0

34.0.0.0/30 is subnetted, 1 subnets
C 34.56.78.0 is directly connected, Serial0/0
C 192.168.3.0/24 is directly connected, FastEthernet1/0
S* 0.0.0.0/0 [1/0] via 34.56.78.1
Router3#



****************************************************************************************
Show ip route state on R3 after Tunnel is established.
****************************************************************************************

Router3#sho ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route

Gateway of last resort is 34.56.78.1 to network 0.0.0.0

34.0.0.0/30 is subnetted, 1 subnets
C 34.56.78.0 is directly connected, Serial0/0
D 192.168.200.0/24 [90/310044416] via 192.168.201.1, 00:00:14, Tunnel0
C 192.168.201.0/24 is directly connected, Tunnel0
D 192.168.1.0/24 [90/297246976] via 192.168.201.1, 00:00:14, Tunnel0
D 192.168.2.0/24 [90/310046976] via 192.168.201.1, 00:00:14, Tunnel0
C 192.168.3.0/24 is directly connected, FastEthernet1/0
S* 0.0.0.0/0 [1/0] via 34.56.78.1
Router3#