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Three-site chain 16 — EIGRP repair
Enterprise Intermediate 5 devices 6 checked tasks 74 points Plan lab
Scenario — Nashik reaches Jabalpur only through the Jodhpur router, a chain of three sites. Everything was configured last week and the network worked. Today the end offices cannot reach each other: one router is running a different autonomous-system number. Find it, fix it and prove the end-to-end paths again. 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
Nashik reaches Jabalpur only through the Jodhpur router, a chain of three sites. Everything was configured last week and the network worked. Today the end offices cannot reach each other: one router is running a different autonomous-system number. Find it, fix it and prove the end-to-end paths again.
Your role: a network engineer on the enterprise team. Level: Intermediate Done when: all 6 goals show as passed (74 points).
Network status
Devices: 3 routers, 2 PCs, cabled as drawn. No Layer 1 or Layer 2 faults: every link is connected and up. R-Nashik starts with addresses (G0/0 10.35.1.1/24, G0/1 172.31.15.1/30) and EIGRP 115 already configured. PC-Nashik is a host with 10.35.1.10/24, gateway 10.35.1.1. R-Jodhpur starts with addresses (G0/0 172.31.15.2/30, G0/1 172.31.15.5/30) and EIGRP 122 already configured. R-Jabalpur starts with addresses (G0/0 10.35.2.1/24, G0/1 172.31.15.6/30) and EIGRP 115 already configured. PC-Jabalpur is a host with 10.35.2.10/24, gateway 10.35.2.1. Known problems
R-Jodhpur has fewer EIGRP neighbours than it has cables to routers, so routes are missing beyond it. No cable or interface is faulty: the fault is one line of configuration on one router. Everything else is correct and must be left alone. Goals
R-Nashik has 1 EIGRP neighbour in AS 115 (8 pts) R-Jodhpur has 2 EIGRP neighbours in AS 115 (8 pts) R-Jabalpur has 1 EIGRP neighbour in AS 115 (8 pts) R-Nashik learns 10.35.2.0/24 from the protocol (10 pts) 10.35.1.10 (Nashik) reaches 10.35.2.10 (Jabalpur) (20 pts) 10.35.2.10 (Jabalpur) reaches 10.35.1.10 (Nashik) (20 pts) The activity, in order
Confirm the symptom: ping the far PC from the near PC and note where it fails. Why: EIGRP shares routes only with neighbours; a mismatched AS number simply never forms one. Verify with: show ip eigrp neighbors Follow the path hop by hop. On each router read its neighbours and its routes, starting with the one nearest the failure. Why: EIGRP shares routes only with neighbours; a mismatched AS number simply never forms one. Verify with: show ip eigrp neighbors Compare the suspect router with its neighbour: the same protocol, the same numbers, every link covered. Why: EIGRP shares routes only with neighbours; a mismatched AS number simply never forms one. Verify with: show ip eigrp neighbors Fix the single wrong line and nothing else. Why: If the prefix is not in the routing table, the router drops packets for it, whatever else is configured. Verify with: show ip route Retest: neighbours, routes, then pings in both directions. Why: A ping needs a route in BOTH directions. This is the end-to-end proof that everything before it worked. Verify with: ping 10.35.2.10 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: Different AS numbers on the two ends — no neighbour and no error Common mistake: Leaving auto-summary on Common mistake: Forgetting that a passive interface forms no neighbours Why this matters
EIGRP is Cisco’s advanced distance-vector protocol: quick convergence and little configuration. Routers become neighbours only when the AS number matches, and automatic summarisation must be off for discontiguous networks.
What you will be able to do
Enable EIGRP with an AS number and wildcard networks
Disable auto-summary
Find an AS mismatch from a missing neighbour
The network
ISR 2911, PC — 5 devices in all, already cabled.
Fa0 Gi0/0 10.35.1.1/24 Fa0 Gi0/0 10.35.2.1/24 Gi0/1 172.31.15.1/30 Gi0/0 172.31.15.2/30 Gi0/1 172.31.15.5/30 Gi0/1 172.31.15.6/30 R-Nashik PC-Nashik 10.35.1.10/24 · gw 10.35.1.1 R-Jodhpur R-Jabalpur PC-Jabalpur 10.35.2.10/24 · gw 10.35.2.1 Drawn from this lab: devices, cables, ports and the addresses already set. Device Model Address already set
R-Nashik ISR 2911 configure it PC-Nashik PC 10.35.1.10 / 255.255.255.0 gw 10.35.1.1 R-Jodhpur ISR 2911 configure it R-Jabalpur ISR 2911 configure it PC-Jabalpur PC 10.35.2.10 / 255.255.255.0 gw 10.35.2.1
Cabling
PC-Nashik Fa0 ↔ R-Nashik Gi0/0 PC-Jabalpur Fa0 ↔ R-Jabalpur Gi0/0 R-Nashik Gi0/1 ↔ R-Jodhpur Gi0/0 R-Jodhpur Gi0/1 ↔ R-Jabalpur 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:
R-Nashik interface g0/0
ip address 10.35.1.1 255.255.255.0
no shutdown
exit
interface g0/1
ip address 172.31.15.1 255.255.255.252
no shutdown
exit
router eigrp 115
network 10.35.1.0 0.0.0.255
network 172.31.15.0 0.0.0.3
no auto-summary
passive-interface GigabitEthernet0/0
exit R-Jodhpur interface g0/0
ip address 172.31.15.2 255.255.255.252
no shutdown
exit
interface g0/1
ip address 172.31.15.5 255.255.255.252
no shutdown
exit
router eigrp 122
network 172.31.15.0 0.0.0.3
network 172.31.15.4 0.0.0.3
no auto-summary
exit R-Jabalpur interface g0/0
ip address 10.35.2.1 255.255.255.0
no shutdown
exit
interface g0/1
ip address 172.31.15.6 255.255.255.252
no shutdown
exit
router eigrp 115
network 10.35.2.0 0.0.0.255
network 172.31.15.4 0.0.0.3
no auto-summary
passive-interface GigabitEthernet0/0
exit 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 R-Nashik has 1 EIGRP neighbour in AS 115 8 On R-Nashik: show ip eigrp neighbors shows at least 1 neighbour(s). 2 R-Jodhpur has 2 EIGRP neighbours in AS 115 8 On R-Jodhpur: show ip eigrp neighbors shows at least 2 neighbour(s). 3 R-Jabalpur has 1 EIGRP neighbour in AS 115 8 On R-Jabalpur: show ip eigrp neighbors shows at least 1 neighbour(s). 4 R-Nashik learns 10.35.2.0/24 from the protocol 10 On R-Nashik: show ip route lists 10.35.2.0/24. 5 10.35.1.10 (Nashik) reaches 10.35.2.10 (Jabalpur) 20 On PC-Nashik: ping 10.35.2.10 must succeed. 6 10.35.2.10 (Jabalpur) reaches 10.35.1.10 (Nashik) 20 On PC-Jabalpur: ping 10.35.1.10 must succeed.
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
Different AS numbers on the two ends — no neighbour and no error
Leaving auto-summary on
Forgetting that a passive interface forms no neighbours
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:
R-Jodhpur no router eigrp 122
router eigrp 115
network 172.31.15.0 0.0.0.3
network 172.31.15.4 0.0.0.3
no auto-summary
exit Where this is examined
CCNA 3.0 EIGRP concepts; CCNP ENCOR/ENARSI EIGRP.
This lab practises these topics in the zNetLaB certification courses:
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