Lab 14.1: BGP Multi-Homing Simulation in GNS3 (Step-by-Step)

By Fathalla Ramadan
February 2026 | Alexandria, Egypt

How do enterprises stay online when one ISP fails?
The answer: BGP multi-homing.

In this lab, you’ll simulate a realistic dual-ISP architecture—just like those used by banks, cloud providers, and smart city projects across Cairo, Riyadh, and beyond.

You’ll configure Enterprise-Edge to connect to two ISPs, advertise its internal network, and maintain connectivity even if one link fails—all using free tools on your laptop.

This is Lab 14.1 from my IP Routing and Switching Lab Handout Book. Now, I’m sharing the full walkthrough—free—for serious learners worldwide.

🎯 What You’ll Learn

Configure eBGP with two different ISPs
Advertise your enterprise network (192.168.10.0/24) to the internet
Achieve automatic failover during ISP outages
Validate reachability to a simulated Web Server

🛠️ What You’ll Need

GNS3 installed (see GNS3 + IOSv Setup Guide)
4 devices:
- Enterprise-Edge (your company router)
- ISP-A
- ISP-B
- Web-Server (simulated internet host)

🌐 IP Addressing Plan (As Specified)

Device	Interface	IP Address	Subnet Mask
Enterprise-Edge	Loopback0	`192.168.10.1`	`255.255.255.0`
	Gig0/0	`10.0.0.2`	`255.255.255.252`
	Gig0/1	`10.0.1.2`	`255.255.255.252`
ISP-A	Gig0/0	`10.0.0.1`	`255.255.255.252`
	Gig0/1	`203.0.113.1`	`255.255.255.0`
ISP-B	Gig0/0	`10.0.1.1`	`255.255.255.252`
	Gig0/1	`198.51.100.1`	`255.255.255.0`
Web-Server	NIC	`203.0.113.10`	`255.255.255.0`

🔧 Step 1: Build the Topology in GNS3

Add 4 devices:
- 3x Cisco IOSv routers → Name: Enterprise-Edge, ISP-A, ISP-B
- 1x Cloud or VPCS → Name: Web-Server (or use a lightweight Linux VM)
Connect:
- Enterprise-Edge Gig0/0 ↔ ISP-A Gig0/0
- Enterprise-Edge Gig0/1 ↔ ISP-B Gig0/0
- ISP-A Gig0/1 ↔ Web-Server

⚙️ Step 2: Configure All Devices

On Enterprise-Edge (AS 65100)

configure terminal
!
interface Loopback0
ip address 192.168.10.1 255.255.255.0
!
interface GigabitEthernet0/0
ip address 10.0.0.2 255.255.255.252
no shutdown
!
interface GigabitEthernet0/1
ip address 10.0.1.2 255.255.255.252
no shutdown
!
router bgp 65100
neighbor 10.0.0.1 remote-as 65001
neighbor 10.0.1.1 remote-as 65002
network 192.168.10.0 mask 255.255.255.0
!
end
write memory

On ISP-A (AS 65001)

configure terminal
!
interface GigabitEthernet0/0
ip address 10.0.0.1 255.255.255.252
no shutdown
!
interface GigabitEthernet0/1
ip address 203.0.113.1 255.255.255.0
no shutdown
!
router bgp 65001
neighbor 10.0.0.2 remote-as 65100
!
ip route 0.0.0.0 0.0.0.0 GigabitEthernet0/1
!
end

On ISP-B (AS 65002)

configure terminal
!
interface GigabitEthernet0/0
ip address 10.0.1.1 255.255.255.252
no shutdown
!
interface GigabitEthernet0/1
ip address 198.51.100.1 255.255.255.0
no shutdown
!
router bgp 65002
neighbor 10.0.1.2 remote-as 65100
!
ip route 0.0.0.0 0.0.0.0 GigabitEthernet0/1
!
end

On Web-Server

Set IP: 203.0.113.10
Set Default Gateway: 203.0.113.1 (ISP-A’s external interface)

🔍 Step 3: Verify BGP & Connectivity

On Enterprise-Edge:bash1
- show ip bgp summary
- → Both neighbors (10.0.0.1, 10.0.1.1) should be Established.
On ISP-A and ISP-B:bash1
- show ip route bgp
- → Both should see: B 192.168.10.0/24 [20/0] via <neighbor>
From Web-Server, ping the enterprise loopback
- ping 192.168.10.1
- → Should succeed via ISP-A.

🧪 Step 4: Test Failover

On Enterprise-Edge, shut down the link to ISP-A
- interface GigabitEthernet0/0
- shutdown
Wait 30–60 seconds.
From Web-Server, ping again
- ping 192.168.10.1
- → Still works! Traffic now flows through ISP-B.

✅ Success: Your enterprise is now multi-homed—resilient by design.

💡 Key Takeaways

eBGP enables communication between autonomous systems (your AS vs. ISPs)
Network statement advertises your internal subnet to the world
Dual upstream links = automatic redundancy
Real internet traffic would reach you via either ISP’s public IP space

📚 Go Deeper

Want the full lab with professional checklists, advanced scenarios (load balancing, AS_PATH prepending), and validation steps?

👉 Get Lab 14.1 in my Lab Handout Book—includes 25 other hands-on labs from VLANs to VXLAN automation.

💬 Final Thought

Multi-homing isn’t just for telecom giants.
In today’s digital economy, every critical service needs resilient connectivity.

And now—you’ve built it yourself.

—
Fathalla Ramadan
Network Architect & Educator
Alexandria, Egypt
35+ years in IT, networking, and technology education across the Middle East and beyond

🔖 Tags:

#BGP #GNS3 #MultiHoming #NetworkingLabs #CCNP #Cisco #NetworkEngineering #FathallaRamadan #HomeLab #GlobalLearners

Tagged gns3