GRE Tunnel Configuration
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GRE is a tunneling protocol that encapsulates packets inside IP to transport traffic across an IP network. The document describes configuring GRE tunnels between routers R1 and R2 to connect their private networks and exchange routing information. This creates a virtual private link between R1 and R2 to pass traffic even though they are connected through the public internet. Interface configurations on R1, R2 and the internet router are provided to establish the GRE tunnels and associated routing.
GRE Tunnel Configuration
- 3. GRE (Generic Routing encapsulation) It is the simplest protocol It encapsulate inside or outside ip address GRE is nothing to do with encryption that IPsec provide We use GRE for Multicast traffic It allow us to start treating the VPN connection like we using private link
- 4. R1 interface Configuration R1(config)#interface serial 1/0 R1(config-if)#description CONNECTED WITH INTERNET R1(config-if)#ip address 100.100.100.2 255.255.255.252 R1(config-if)#no shut R1(config-if)#exit R1(config)#interface fastEthernet 0/0 R1(config-if)#description CONNECTED WITH SW1 R1(config-if)#ip address 192.168.2.1 255.255.255.0 R1(config-if)#no shut R1(config-if)#exit
- 5. Internet Router interface Configuration internet(config)#interface serial 1/0 internet(config-if)#description CONNECTED WITH R1 internet(config-if)#ip address 100.100.100.1 255.255.255.252 internet(config-if)#clock rate 64000 internet(config-if)#no shut internet(config-if)#exit internet(config)#interface serial 1/1 internet(config-if)#description CONNECTED WITH R2 internet(config-if)#ip address 200.200.200.1 255.255.255.252 internet(config-if)#clock rate 64000 internet(config-if)#no shut internet(config-if)#exit
- 6. Router 2 interface Configuration R2(config)#interface serial 1/1 R2(config-if)#description CONNECTED WITH INTERNET R2(config-if)#ip address 200.200.200.2 255.255.255.252 R2(config-if)#no shut R2(config-if)#exit R2(config)#interface fastEthernet 0/0 R2(config-if)#description CONNECTED WITH SW2 R2(config-if)#ip address 10.250.250.1 255.255.255.0 R2(config-if)#no shut R2(config-if)#exit
- 7. GRE Tunnel interface Configuration in R1 and R2 R1(config)#interface tunnel 1 (1:- Tunnel Number) R1(config-if)#description TUNNEL DIRECTLY CONNECTING TO R2 R1(config-if)#tunnel source 100.100.100.2 (source Public ip address of R1) R1(config-if)#tunnel destination 200.200.200.2 (Destination Public ip address of R2) R1(config-if)#ip address 172.16.16.1 255.255.255.252 (Private ip address for Tunnel) R1(config-if)#exit
- 8. R2(config)#interface tunnel 2 (2:- Tunnel Number) R2(config-if)#description TUNNEL DIRECTLY CONNECTING TO R1 R2(config-if)#tunnel source 200.200.200.2 (source Public ip address of R2) R2(config-if)#tunnel destination 100.100.100.2 (Destination Public ip address of R1) R2(config-if)#ip address 172.16.16.2 255.255.255.252 (Private ip address for Tunnel) R2(config-if)#exit
- 9. Protocol Configuration in R1 and R2 to exchange their route R1(config)#router rip R1(config-router)#version 2 R1(config-router)#network 192.168.2.0 {R1 internal network} R1(config-router)#network 172.16.16.0 {R1 Tunnel Network} R1(config-router)#no auto-summary R1(config-router)#exit Ø R1(config)#ip route 0.0.0.0 0.0.0.0 s1/0 {default route to internet}
- 10. R2(config)#router rip R2(config-router)#version 2 R2(config-router)#network 10.250.250.0 {R2 internal network} R2(config-router)#network 172.16.16.0 {R2 Tunnel Network} R2(config-router)#no auto-summary R2(config-router)#exit R2(config)#ip route 0.0.0.0 0.0.0.0 s1/1 {default route to internet}
- 11. Troubleshooting & Verification Commands Show ip interface brief Show ip route Show interfaces tunnel 2 (Tunnel Number) Verify using Traceroute from PC1 to PC2 All the traffic will go through Tunnel GRE tunnel acts as all the devices are connected in same Ethernet segment And also It hides the public address