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
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
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
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
