Lab 03 — OSPF Multi-Area — OSPFv2 & OSPFv3

Network Topology

Prerequisites

›Understand OSPF LSA types 1-7
›Know OSPF area types: backbone, stub, NSSA
›Familiarity with OSPF network types

Task Sheet — CCIE Exam Format

Task 1Medium

Enable OSPF process 1 on CORE-1 through CORE-4 and EDGE-1 through EDGE-4. All backbone links in Area 0. Configure router-IDs from Loopback0.

✓ Verify: show ip ospf neighbor

Task 2Hard

Configure all P2P backbone links as point-to-point network type. Enable MD5 authentication using key-chain KC-OSPF-AUTH with key 'Nx9#mP2@qK'.

✓ Verify: show ip ospf interface GigabitEthernet1

Task 3Hard

Enable BFD on all OSPF neighbors (bfd all-interfaces under router ospf). Use interval 300ms min_rx 300ms multiplier 3.

✓ Verify: show bfd neighbors

Task 4Hard

Configure OSPF stub area 10 on the CE-CORP-1 segment. Verify only default route is received by CE routers (no external LSAs).

✓ Verify: show ip ospf database summary

Task 5Hard

Enable OSPFv3 (IPv6) process 1 on all backbone interfaces. Redistribute connected IPv6 prefixes from CE networks.

✓ Verify: show ipv6 ospf neighbor

Task 6Expert

Configure LSA throttling: lsa-arrival 100ms, throttle lsa 0ms 50ms 200ms. Configure SPF throttle 50ms 100ms 5000ms.

✓ Verify: show ip ospf | include Throttle

Key Concepts

OSPF multi-area design confines LSA flooding to within each area, reducing SPF computation overhead on all routers. Area 0 (backbone) interconnects all other areas through ABRs. Type 3 LSAs carry summary routes between areas; filtering these at ABRs controls inter-area topology visibility.

OSPF authentication using key-chains allows cryptographic algorithm selection (MD5, HMAC-SHA) and key rollover without adjacency drops. The key-chain must exist on both sides with overlapping key send/accept lifetimes. Always use 'key-string' under the key, not 'accept-lifetime' alone.

BFD (Bidirectional Forwarding Detection) provides sub-second failure detection independent of routing protocol hello timers. BFD runs a separate lightweight protocol; when it detects a failure, it notifies OSPF immediately rather than waiting for dead-interval expiry (typically 40 seconds). This reduces convergence time from 40s to sub-300ms.

Verification Commands

show ip ospf neighbor

All neighbors: FULL/ — (point-to-point shows no DR/BDR)

show ip ospf database

Area 0: Router LSAs from all 8 routers, Network LSA none (p2p)

show bfd neighbors

All BFD sessions Up with interval 300ms

show ip route ospf

O routes via multiple OSPF paths

Common Mistakes & Troubleshooting

OSPF adjacency stuck in EXSTART/EXCHANGE

MTU mismatch is the most common cause. Check 'ip ospf mtu-ignore' or align MTU. Also verify authentication key matches exactly including case.

BFD session not establishing

Verify BFD is enabled on both sides of the link. Check 'show bfd neighbors' — sessions require bidirectional UDP packets on port 3784. Ensure no ACL blocking UDP 3784.

Stub area receiving type 5 LSAs

Verify 'area X stub' is configured on ALL routers in the area — missing it on one router causes them to not be in the stub area. ABR must also have the stub config.

Solution Configs

Attempt the tasks yourself before viewing solutions.
Type SOLUTION to unlock.

CORE-1

hostname CORE-1
!
interface Loopback0
 ip address 10.255.1.1 255.255.255.255
!
interface GigabitEthernet1
 ip address 10.0.12.0 255.255.255.254
 ip ospf network point-to-point
 ip ospf 1 area 0
 bfd interval 300 min_rx 300 multiplier 3
 ip ospf bfd
!
router ospf 1
 router-id 10.255.1.1
 passive-interface Loopback0
 network 10.255.1.1 0.0.0.0 area 0
 mpls ldp autoconfig
 bfd all-interfaces

Research and direction by Ioannis (John) Konstas; compiled and finalized with AI assistance.