Lab 1: OSPF Multi-Area Topology and LSDB Convergence

Chapter: 1 (Routing I: OSPF)
Duration: 90 minutes
Tools: Containerlab, FRRouting (FRR), Wireshark, vtysh
Points: 10

Objectives

By the end of this lab you will:

1. Build a 4-router, 3-area OSPF topology using Containerlab and FRR
2. Observe OSPF neighbor state progression from Down to Full
3. Inspect the LSDB and identify LSA types 1, 2, and 3
4. Force a link failure and measure convergence time
5. Verify inter-area routing works through an ABR

Topology

Area 0 (Backbone):
  R1 (10.0.12.1) ---- R2 (10.0.12.2)
  Lo: 1.1.1.1          Lo: 2.2.2.2 (ABR)

Area 1:
  R2 (10.0.23.1) ---- R3 (10.0.23.2)
                       Lo: 3.3.3.3

Area 2:
  R2 (10.0.24.1) ---- R4 (10.0.24.2)
                       Lo: 4.4.4.4

R2 is the ABR connecting Area 1 and Area 2 to Area 0. R3 and R4 are internal routers in Areas 1 and 2 respectively.

Setup

1. Create the topology file

# File: topo-ospf4.clab.yml
name: ospf4
topology:
  nodes:
    r1:
      kind: linux
      image: frrouting/frr:latest
    r2:
      kind: linux
      image: frrouting/frr:latest
    r3:
      kind: linux
      image: frrouting/frr:latest
    r4:
      kind: linux
      image: frrouting/frr:latest
  links:
    - endpoints: ["r1:eth1", "r2:eth1"]   # Area 0 link
    - endpoints: ["r2:eth2", "r3:eth1"]   # Area 1 link
    - endpoints: ["r2:eth3", "r4:eth1"]   # Area 2 link

containerlab deploy -t topo-ospf4.clab.yml

2. Enable OSPF daemon on each container

# On each container, enable ospfd and zebra
docker exec clab-ospf4-r1 bash -c "
  sed -i 's/ospfd=no/ospfd=yes/' /etc/frr/daemons
  service frr restart"
# Repeat for r2, r3, r4

3. Configure IP addresses

# R1
docker exec -it clab-ospf4-r1 vtysh

configure terminal
interface eth1
 ip address 10.0.12.1/30
!
interface lo
 ip address 1.1.1.1/32
!
router ospf
 router-id 1.1.1.1
 auto-cost reference-bandwidth 10000
 network 10.0.12.0/30 area 0
 network 1.1.1.1/32 area 0
!

Repeat with appropriate addresses on R2 (ABR: configure eth1 in area 0, eth2 in area 1, eth3 in area 2), R3 (area 1), and R4 (area 2).

Exercises

Exercise 1: Neighbor State Observation (20 min)

Watch OSPF neighbor establishment in real-time:

# Terminal 1: watch neighbor table update on R1
watch -n 1 "docker exec clab-ospf4-r1 vtysh -c 'show ip ospf neighbor'"

# Terminal 2: capture OSPF packets on R1's eth1 interface
docker exec clab-ospf4-r1 tcpdump -i eth1 -n "proto ospf" -w /tmp/ospf_hellos.pcap &

Record:

1. How many seconds elapsed from the first Hello received to the Full state?
2. What is R1's Router ID? What is R2's Router ID?
3. What is the DR/BDR on the R1-R2 segment? How was it elected? (Hint: compare Bridge IDs / RIDs)

Open /tmp/ospf_hellos.pcap in Wireshark. Identify: Hello, DBD, LSR, LSU, and LSAck packets.

Exercise 2: LSDB Inspection (20 min)

After all adjacencies reach Full state:

# View full LSDB on R3 (Area 1 internal router)
docker exec clab-ospf4-r3 vtysh -c "show ip ospf database"

# View only Type 3 Summary LSAs
docker exec clab-ospf4-r3 vtysh -c "show ip ospf database summary"

# View routing table on R3
docker exec clab-ospf4-r3 vtysh -c "show ip route ospf"

Record:

1. How many LSAs are in R3's LSDB? List each by type (Router/Network/Summary/etc.)
2. Does R3 have a Type 1 (Router) LSA for R4? Why or why not?
3. Does R3 have a Type 3 (Summary) LSA that covers R4's loopback (4.4.4.4/32)?
4. What is the routing table entry for 4.4.4.4/32 on R3? Mark it as O IA (inter-area)?
5. What is the next-hop for R3 to reach R4?

Exercise 3: Convergence Measurement (30 min)

Baseline measurement:

# Start continuous ping from R3 to R4's loopback
docker exec -it clab-ospf4-r3 sh -c "ping -i 0.2 -c 500 4.4.4.4" > /tmp/ping_baseline.txt &

# In another terminal: watch the OSPF neighbor table
watch -n 0.2 "docker exec clab-ospf4-r2 vtysh -c 'show ip ospf neighbor'"

Force a link failure:

# Disable the R2-R4 link (simulates link failure)
docker exec clab-ospf4-r4 ip link set eth1 down

Record:

1. How many ping packets were lost between when you disabled the link and when pings to 4.4.4.4 failed completely?
2. How long (in seconds) until R3 could no longer reach R4?
3. How long (in seconds) until R2's neighbor table showed R4 as Down?
4. What OSPF dead interval explains this convergence time?

Restore and tune:

# Restore the link
docker exec clab-ospf4-r4 ip link set eth1 up

# Now configure BFD to reduce detection time
docker exec -it clab-ospf4-r2 vtysh

configure terminal
bfd
 peer 10.0.24.2 local-address 10.0.24.1
  detect-multiplier 3
  receive-interval 300
  transmit-interval 300
 !
!
interface eth3
 ip ospf bfd
!

Repeat the link failure test with BFD enabled. Record the new convergence time.

Exercise 4: Reference Bandwidth Verification (10 min)

# Check the cost of R1's eth1 interface
docker exec clab-ospf4-r1 vtysh -c "show ip ospf interface eth1"

Record:

1. What is the current cost of R1's eth1 interface?
2. If the interface bandwidth is 10 Gbps and you set auto-cost reference-bandwidth 10000, what should the cost be?
3. Change the reference bandwidth and verify the cost changes.

Lab Report

Submit a short lab report (1-2 pages, or annotated terminal output) answering:

1. What is the relationship between the OSPF Hello timer, Dead interval, and convergence time?
2. R3 sees R4's network as O IA (inter-area). What LSA type is responsible for this route, and which router generated it?
3. What is BFD's role in reducing convergence time? What is the minimum BFD detection time with detect-multiplier 3 and receive-interval 300?
4. Why does OSPF have a Designated Router on multi-access segments? What problem does it solve?

Cleanup

containerlab destroy -t topo-ospf4.clab.yml

Grading (10 points)