Multi-Area OSPF Lab

• This is a practical multi-area OSPF lab designed to demonstrate hierarchical OSPF design.
• The lab includes 5 OSPF areas (0, 1, 2, 3, and 14) with proper ABR placement and external route redistribution via ASBR.
• The end goal is to achieve full connectivity between all areas while maintaining OSPF hierarchical design principles.

Network Topology & Addressing

Device	Interface	IP Address	Area	Notes
BBR	G0/0	10.12.0.1/16	0	Backbone Router
	Router ID	1.1.1.1		Priority: 255
ABR1	G0/0	10.12.0.2/16	0	Link to Area 0
	G0/1	10.20.0.1/16	1	Link to Area 1
	Router ID	1.1.1.2		Area Border Router
ABR2	G0/0	10.12.0.3/16	0	Link to Area 0
	G0/1	172.16.0.1/24	2	Link to Area 2
	Router ID	1.1.1.3		Area Border Router
ABR3	G0/0	10.12.0.4/16	0	Link to Area 0
	G0/1	192.168.3.1/24	3	Link to Area 3
	Router ID	1.1.1.4		Area Border Router
ASBR	G0/0	10.12.0.5/16	0	Link to Area 0
	G0/1	209.30.17.1/30	14	External/Internet
	Router ID	1.1.1.5		AS Boundary Router
IR0	G0/0	10.20.0.2/16	1	Internal Router
	Router ID	1.1.2.1
IR1	G0/0	10.20.0.3/16	1	Internal Router
	Router ID	1.1.2.2
IR2	G0/0	10.20.0.4/16	1	Internal Router
	Router ID	1.1.2.3
IR3	G0/0	172.16.0.2/24	2	Internal Router
	Router ID	1.1.3.1
IR4	G0/0	172.16.0.3/24	2	Internal Router
	Router ID	1.1.3.2
IR5	G0/0	192.168.3.2/24	3	Internal Router
	Router ID	1.1.4.1
IR6	G0/0	192.168.3.3/24	3	Internal Router
	Router ID	1.1.4.2

Configuration Highlights

• Area 0 serves as the backbone area connecting all other areas through ABRs
• ABRs connect non-backbone areas to Area 0, maintaining OSPF hierarchical design
• ASBR redistributes external routes and provides default route injection
• Router IDs follow structured2 numbering: Area 0 (1.1.1.x), Area 1 (1.1.2.x), etc.
• Interface costs are configured to influence optimal path selection

Important Configuration

BBR (Backbone Router) Configuration

router ospf 1
network 10.12.0.0 0.0.255.255 area 0
router-id 1.1.1.1

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ABR1 (Area Border Router) Configuration

router ospf 1
network 10.12.0.0 0.0.255.255 area 0
network 10.20.0.0 0.0.255.255 area 1
router-id 1.1.1.2

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ABR2 (Area Border Router) Configuration

router ospf 1
network 10.12.0.0 0.0.255.255 area 0
network 172.16.0.0 0.0.0.255 area 2
router-id 1.1.1.3

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ABR3 (Area Border Router) Configuration

router ospf 1
network 10.12.0.0 0.0.255.255 area 0
network 192.168.3.0 0.0.0.255 area 3
router-id 1.1.1.4

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ASBR (Autonomous System Boundary Router) Configuration

router ospf 1
network 10.12.0.0 0.0.255.255 area 0
network 209.30.17.0 0.0.0.3 area 14
router-id 1.1.1.5
default-information originate
!
ip route 0.0.0.0 0.0.0.0 209.30.17.1

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Internal Router (IR0) Configuration (Is the same for the other IRs)

router ospf 1
network 10.20.0.0 0.15.255.255 area 1
router-id 1.1.2.1

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Routing Table for All Routers

ABR1

ABR2

ABR3

ASBR

BBR

OSPF Cost Change (On All routers)

interface GigabitEthernet0/0
ip ospf cost 10000

Verification Commands

Check OSPF Neighbors

show ip ospf neighbor
show ip ospf neighbor detail

Verify OSPF Database

show ip ospf database
show ip ospf database summary
show ip ospf database external

Check Routes

show ip route ospf
show ip ospf border-routers

Verify Areas

show ip ospf
show ip ospf interface brief

Test Connectivity

ping 10.20.1.1 source 192.168.3.1
ping 172.16.0.1 source 10.20.1.1
traceroute 192.168.3.1 source 10.20.1.1

Expected Results

• Area 0: Should see all ABRs as neighbors
• ABR1: Should have neighbors in both Area 0 and Area 1
• Internal Routers: Should only see neighbors within their own area
• ASBR: Should advertise default route (0.0.0.0/0) to all areas
• Inter-area routes: Should appear as O IA (OSPF Inter-Area) in routing table
• External routes: Should appear as O E1 or O E2 in routing table

Troubleshooting Tips

• Ensure Area 0 connectivity for all ABRs
• Verify Router IDs are unique across the entire OSPF domain
• Check area numbers match on both sides of links
• Confirm authentication keys match on connected interfaces
• Use debug ip ospf events for adjacency issues

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Thank you for reviewing this project. You are welcome to use, adapt, or extend this project for educational or lab purposes.

For questions, suggestions, or improvements, feel free to contribute or open an issue.