zNetLaB › Guided labs › Enterprise
OSPF inter-area summarisation at the ABR
Enterprise Advanced 3 devices 3 checked tasks 100 points Plan lab
Area 1 holds four /24 networks. Every router in the backbone is carrying all four, and every flap in area 1 is flooded to all of them. Summarise at the area border router so the backbone sees one /22 — and confirm the specifics are gone from the other side. You build it in a browser, type real commands at each device, and every task below is
checked against the running configuration — so you find out it is wrong before anybody else does.
Open this lab in the simulator
The simulator runs in your browser with nothing to install. This lab is part of the full simulator: open it free for 7 days with a new account, then with a plan. It needs an account, which keeps your progress.
The scenario
Area 1 holds four /24 networks. Every router in the backbone is carrying all four, and every flap in area 1 is flooded to all of them. Summarise at the area border router so the backbone sees one /22 — and confirm the specifics are gone from the other side.
Your role: a network engineer on the enterprise team. Level: Advanced Done when: all 3 goals show as passed (100 points).
Network status
Devices: 3 routers, cabled as drawn. No Layer 1 or Layer 2 faults: every link is connected and up. R1-Area1 starts with addresses (G0/1 10.0.1.1/30, L1 10.1.0.1/24, L2 10.1.1.1/24, L3 10.1.2.1/24, L4 10.1.3.1/24) and OSPF 1 already configured. ABR starts with addresses (G0/0 10.0.1.2/30, G0/1 10.0.2.1/30) and OSPF 1 already configured. R3-Backbone starts with addresses (G0/1 10.0.2.2/30) and OSPF 1 already configured. Known problems
None: nothing is misconfigured. The network is simply not finished: what the goals list is what you have to build or secure. Goals
The ABR summarises area 1 with one range (30 pts) The backbone router learns the summary 10.1.0.0/22 as an inter-area route (40 pts) The individual /24s are no longer in the backbone (30 pts) The activity, in order
The ABR summarises area 1 with one range Why: This is the task that checks your configuration directly: the line must really be there, not just look right. Verify with: show running-config The backbone router learns the summary 10.1.0.0/22 as an inter-area route Why: The code tells you HOW a route was learned, which tells you which process to look at if it is wrong. Verify with: show ip route The individual /24s are no longer in the backbone Why: A route that should not exist is a leak or a loop waiting to happen. Verify with: show ip route Tips
Work in the order given: later goals depend on the earlier ones. After every change, run the verify command before moving on; do not guess. Stuck? Read the verify output first. It names the interface, neighbour or route that is wrong. Common mistake: Summarising at a non-ABR router Common mistake: A range that covers networks that do not exist Common mistake: Forgetting the summary is only for inter-area routes Why this matters
Without summarisation every flap in an area is flooded to every router in the backbone. An area range on the ABR turns many specific networks into one and hides the instability.
What you will be able to do
Configure inter-area summarisation with area range
Explain what the ABR still keeps (a discard route) and what other routers see
Verify O IA summary routes and the absence of specifics
The network
ISR 2911 — 3 devices in all, already cabled.
Gi0/1 10.0.1.1/30 Gi0/0 10.0.1.2/30 Gi0/1 10.0.2.1/30 Gi0/1 10.0.2.2/30 R1-Area1 ABR R3-Backbone Drawn from this lab: devices, cables, ports and the addresses already set. Device Model Address already set
R1-Area1 ISR 2911 configure it ABR ISR 2911 configure it R3-Backbone ISR 2911 configure it
Cabling
R1-Area1 Gi0/1 ↔ ABR Gi0/0 ABR Gi0/1 ↔ R3-Backbone Gi0/1
What is configured at the start
These are already configured when the lab opens — including, where this is a troubleshooting lab, the fault itself:
R1-Area1 interface g0/1
ip address 10.0.1.1 255.255.255.252
no shutdown
exit
interface lo1
ip address 10.1.0.1 255.255.255.0
no shutdown
exit
interface lo2
ip address 10.1.1.1 255.255.255.0
no shutdown
exit
interface lo3
ip address 10.1.2.1 255.255.255.0
no shutdown
exit
interface lo4
ip address 10.1.3.1 255.255.255.0
no shutdown
exit
router ospf 1
router-id 1.1.1.1
network 10.0.1.0 0.0.0.3 area 1
network 10.1.0.0 0.0.3.255 area 1 ABR interface g0/0
ip address 10.0.1.2 255.255.255.252
no shutdown
exit
interface g0/1
ip address 10.0.2.1 255.255.255.252
no shutdown
exit
router ospf 1
router-id 2.2.2.2
network 10.0.1.0 0.0.0.3 area 1
network 10.0.2.0 0.0.0.3 area 0 R3-Backbone interface g0/1
ip address 10.0.2.2 255.255.255.252
no shutdown
exit
router ospf 1
router-id 3.3.3.3
network 10.0.2.0 0.0.0.3 area 0 Tasks, and how each one is checked
Every task is decided by reading the live network — a neighbour in FULL, a ping that succeeds, a line in the running configuration — not by looking for a keyword you typed. The same command shows you what the lab sees.
# Task Pts How to verify it yourself
1 The ABR summarises area 1 with one range 30 On ABR: show running-config contains the line(s) matching area 1 range 10\.1\.0\.0 255\.255\.252\.0. 2 The backbone router learns the summary 10.1.0.0/22 as an inter-area route 40 On R3-Backbone: show ip route lists 10.1.0.0/22 with code O IA. 3 The individual /24s are no longer in the backbone 30 On R3-Backbone: show ip route does not list 10.1.1.0/24.
Stuck? Ask the coach
Tell the coach what you see or what you tried. It gives you a hint, not the answer, the way a senior engineer would. Included with a free trial or any plan.
Ask the coach
Common mistakes
Summarising at a non-ABR router
A range that covers networks that do not exist
Forgetting the summary is only for inter-area routes
Reference solution
Try it yourself first — the lab checks your work either way. This is one configuration that makes every task pass, device by device:
ABR router ospf 1
area 1 range 10.1.0.0 255.255.252.0
exit Where this is examined
CCNP ENARSI (OSPF), CCIE EI (OSPF at scale).
This lab practises these topics in the zNetLaB certification courses:
Related labs
Where to start
The lessons all guided labs plans
CCNA®, CCNP® and Cisco® are trademarks of Cisco Systems, Inc. zNetLaB is not affiliated with or endorsed by Cisco.