LAB Practice: Internet Access with GRE Tunnel between HO and BR (Part-2)

 

In the previous part of this lab, we established a GRE tunnel between the Head Office (HO) and Branch Office (BR). In Part-2, we will extend the setup to provide Internet access to both offices through the GRE tunnel. This setup is essential for simulating real-world scenarios where branch offices access external resources through a central office.

Lab Objectives

1. Enable internet access for both HO and BR through GRE tunnel.

2. Configure routing to ensure traffic is properly forwarded to the Internet.

3. Test connectivity using ping and traceroute commands.

Network Topology

Here is the simplified network topology for this lab:

[HO Router] --------GRE Tunnel-------- [BR Router]

       |                                    |

    Internet                              Branch LAN

HO Router: Connected to Internet.

BR Router: Connected to Branch LAN, traffic routed via GRE tunnel to HO.

Configuration Steps

1. Configure NAT on HO Router

To allow the BR office to access the Internet, NAT (Network Address Translation) must be enabled on the HO router.

interface Gig0/0

 ip address 203.0.113.1 255.255.255.0

 ip nat outside

interface Tunnel0

 ip address 10.0.0.1 255.255.255.0

 ip nat inside

ip access-list standard NAT_ACL

 permit 10.0.0.0 0.0.0.255

ip nat inside source list NAT_ACL interface Gig0/0 overload

> Explanation:

ip nat inside is applied on tunnel interface.

ip nat outside is applied on the public interface connected to Internet.

overload allows multiple internal IPs to use a single public IP.

2. Configure Default Route on BR Router

The branch router must send all Internet-bound traffic through the GRE tunnel.

ip route 0.0.0.0 0.0.0.0 10.0.0.1

> Explanation:

All unknown traffic (0.0.0.0/0) from BR router will be forwarded to HO via the GRE tunnel.

3. Test Connectivity

After configuration, verify Internet access:

ping 8.8.8.8

traceroute 8.8.8.8

Successful ping confirms Internet connectivity.

Traceroute shows traffic passing through HO Router.

Troubleshooting Tips

1. Ping fails:

Check GRE tunnel status with show ip interface brief.

Verify NAT configuration on HO router.

2. Routing issues:

Ensure default route on BR points to GRE tunnel IP of HO.

3. Internet access slow or unstable:

Verify bandwidth and tunnel stability.

Conclusion

By completing Part-2 of this lab, we have successfully provided Internet access to branch office through a GRE tunnel. This is a common setup in enterprise networks where remote offices rely on central sites for external connectivity.

Next steps could include VPN encryption, advanced NAT policies, and dynamic routing protocols over the GRE tunnel for better scalability.