BGP & OSPF Multi-Area Routing Lab: ISP Peering & Route Redistribution

Introduction

This lab simulates an enterprise network peering with two ISP routers via BGP, while utilizing a multi-layered, multi-area OSPF topology for internal routing. The goal of this setup is to explore BGP peering, OSPF multi-area configuration, route redistribution, VLAN segmentation, DHCP services, and external DNS integration.

This is part of my Bits of Progress journey, where I document my hands-on networking experience. Rather than a step-by-step tutorial, this blog post presents my thought process, configurations, and the learning experience gained from building this lab.

Lab Topology Overview

Key Components:

ISP Routers (BGP AS 65010 & 65020) – Simulate two separate ISPs peering with the enterprise network.
Core Routers (BGP AS 65001, OSPF Backbone Area 0) – Serve as the backbone of the enterprise, interconnecting various OSPF areas and managing route redistribution.
Access Routers (OSPF Area 1, DHCP Services) – Provide connectivity to end devices in separate VLANs.
Access Switches (Layer 2 VLAN Segmentation) – Facilitate communication between clients, servers, and IoT devices.
ISP Exchange Router (BGP AS 65050) – Acts as an intermediary router simulating upstream internet access.

Configuration Breakdown

1. BGP Peering & Route Redistribution

The core routers establish BGP sessions with the ISP routers while also redistributing internal OSPF routes into BGP.

CoreRouter1 BGP Configuration:

router bgp 65001
 bgp log-neighbor-changes
 aggregate-address 192.168.0.0 255.255.0.0 summary-only
 aggregate-address 10.0.0.0 255.0.0.0 summary-only
 redistribute ospf 1 match internal external 1 external 2
 neighbor 172.16.2.1 remote-as 65010

Redistributes OSPF routes into BGP, allowing the enterprise network to advertise summarized internal networks to the ISPs.
Uses aggregate addressing to reduce the number of advertised routes.

ISPRouter1 & ISPRouter2 BGP Configuration:

router bgp 65010
 bgp log-neighbor-changes
 network 172.16.1.0 mask 255.255.255.252
 network 172.16.2.0 mask 255.255.255.252
 neighbor 172.16.1.2 remote-as 65020
 neighbor 172.16.2.2 remote-as 65001
 neighbor 172.16.2.2 route-map ADVERTISE-DEFAULT-ROUTE out
 neighbor 172.16.4.1 remote-as 65050

router bgp 65020
 bgp log-neighbor-changes
 network 172.16.3.0 mask 255.255.255.252
 network 172.16.5.0 mask 255.255.255.252
 neighbor 172.16.1.1 remote-as 65010
 neighbor 172.16.3.2 remote-as 65001
 neighbor 172.16.3.2 route-map ADVERTISE-DEFAULT-ONLY out
 neighbor 172.16.5.1 remote-as 65050

Both ISPs advertise a default route to the enterprise network.
ISPRouter2 (AS 65020) also peers with ISPRouter1 (AS 65010), forming a redundant external connection.

2. OSPF Multi-Area Design

The enterprise network follows a structured OSPF design with multiple areas for efficient routing and scalability.

CoreRouter1 OSPF Configuration:

router ospf 1
 router-id 1.1.1.1
 network 10.1.0.0 0.0.0.3 area 0
 network 10.1.1.0 0.0.0.3 area 0
 network 10.1.2.0 0.0.0.3 area 0
 default-information originate metric-type 1

OSPF Backbone (Area 0) connects all access routers.
Advertises the default route to propagate internet access throughout the network.

AccessRouter1 OSPF Configuration:

router ospf 1
 router-id 2.2.1.1
 network 192.168.10.0 0.0.0.255 area 1
 network 192.168.20.0 0.0.0.255 area 1
 network 192.168.30.0 0.0.0.255 area 1

Belongs to Area 1 and connects local VLANs to the enterprise network.
Establishes an OSPF adjacency with CoreRouter1.

3. VLANs, Subnets, and DHCP

Each Access Router provides DHCP services for clients, servers, and IoT devices.

AccessRouter1 DHCP Configuration:

ip dhcp pool CLIENTS1
 network 192.168.10.0 255.255.255.0
 default-router 192.168.10.1
 dns-server 8.8.8.8

Assigns IPs dynamically to devices in VLAN 10 (Clients).
Uses Google’s DNS (8.8.8.8) for external name resolution.

Testing & Validation

1. BGP Neighbor Verification

Checking BGP peers from CoreRouter1:

CoreRouter1# show ip bgp summary

Ensures BGP sessions are established with ISP routers.

2. OSPF Neighbor Verification

Checking OSPF neighbors on AccessRouter1:

AccessRouter1# show ip ospf neighbor

Confirms OSPF adjacencies with CoreRouter1.

3. Route Summarization Check

Checking advertised routes on ISP Routers:

ISPRouter1# show ip bgp

Confirms that only summarized routes are advertised to the ISPs.

Conclusion

This lab was a great learning experience in BGP peering, OSPF multi-area routing, and network services like VLANs and DHCP. By configuring an ISP environment and enterprise network, I gained hands-on insight into real-world networking scenarios.

This is just one step in my Bits of Progress journey. Stay tuned for more labs and technical deep dives.

📺 Watch the Lab in Action: https://youtu.be/cb68HlbxOk8
📂 Download Config Files: https://github.com/PRivers251/RoutingLab_BGP_OSPF_3-6-25