zNetLaB › Guided labs › Telecom
Service provider core — OSPF underlay + iBGP overlay
Telecom Advanced 7 devices 5 checked tasks 100 points Plan lab
Two PEs and a P router run OSPF for reachability, then iBGP carries the customer prefixes end to end. 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
Two PEs and a P router run OSPF for reachability, then iBGP carries the customer prefixes end to end.
Your role: a network engineer. Level: Advanced Done when: all 5 goals show as passed (100 points).
Network status
Devices: 5 routers, 2 PCs, cabled as drawn. No Layer 1 or Layer 2 faults: every link is connected and up. CE1 starts with addresses (G0/1 172.16.1.1/24, G0/0 10.1.1.2/30) and static routes already configured. CE2 starts with addresses (G0/1 172.16.2.1/24, G0/0 10.2.2.2/30) and static routes already configured. Site-A is a host with 172.16.1.10/24, gateway 172.16.1.1. Site-B is a host with 172.16.2.10/24, gateway 172.16.2.1. PE1, P1, PE2 start with an empty configuration. Known problems
The network worked and now does not: the scenario above says what users report. The cause is a configuration fault, not a cable. Find it with show commands (interfaces, routes, neighbours, running-config) before you change anything; fix only what is wrong. Goals
PE1 ↔ P1 ↔ PE2 core links addressed and up (15 pts) OSPF area 0 adjacencies formed across the core (20 pts) PE1 learns PE2 loopback via OSPF (15 pts) iBGP session PE1 ↔ PE2 is Established (20 pts) Site-A reaches Site-B end to end (30 pts) The activity, in order
PE1 ↔ P1 ↔ PE2 core links addressed and up Why: A router interface routes nothing until it has an address and is up. Every other task builds on this one. Verify with: show ip interface brief OSPF area 0 adjacencies formed across the core Why: OSPF routes only flow over a FULL adjacency. If a neighbour is stuck in INIT or EXSTART, compare the two ends’ settings. Verify with: show ip ospf neighbor PE1 learns PE2 loopback via OSPF 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 iBGP session PE1 ↔ PE2 is Established Why: BGP does nothing until the TCP session is Established. Active or Idle means a wrong AS number, no route to the peer, or a block. Verify with: show ip bgp summary Site-A reaches Site-B end to end Why: A ping needs a route in BOTH directions. This is the end-to-end proof that everything before it worked. Verify with: ping 172.16.2.10 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. Why this matters
Two PEs and a P router run OSPF for reachability, then iBGP carries the customer prefixes end to end.
What you will be able to do
PE1 ↔ P1 ↔ PE2 core links addressed and up
OSPF area 0 adjacencies formed across the core
PE1 learns PE2 loopback via OSPF
iBGP session PE1 ↔ PE2 is Established
The network
CE Router, PE Router, P Router, PC — 7 devices in all, already cabled.
Fa0 Gi0/1 172.16.1.1/24 Gi0/0 10.1.1.2/30 Gi0/0 Gi0/1 Gi0/0 Gi0/1 Gi0/1 Gi0/0 Gi0/0 10.2.2.2/30 Gi0/1 172.16.2.1/24 Fa0 CE1 PE1 P1 PE2 CE2 Site-A 172.16.1.10/24 · gw 172.16.1.1 Site-B 172.16.2.10/24 · gw 172.16.2.1 Drawn from this lab: devices, cables, ports and the addresses already set. Device Model Address already set
CE1 CE Router configure it PE1 PE Router configure it P1 P Router configure it PE2 PE Router configure it CE2 CE Router configure it Site-A PC 172.16.1.10 / 255.255.255.0 gw 172.16.1.1 Site-B PC 172.16.2.10 / 255.255.255.0 gw 172.16.2.1
Cabling
Site-A Fa0 ↔ CE1 Gi0/1 CE1 Gi0/0 ↔ PE1 Gi0/0 PE1 Gi0/1 ↔ P1 Gi0/0 P1 Gi0/1 ↔ PE2 Gi0/1 PE2 Gi0/0 ↔ CE2 Gi0/0 CE2 Gi0/1 ↔ Site-B Fa0
What is configured at the start
These are already configured when the lab opens — including, where this is a troubleshooting lab, the fault itself:
CE1 interface g0/1
ip address 172.16.1.1 255.255.255.0
no shutdown
exit
interface g0/0
ip address 10.1.1.2 255.255.255.252
no shutdown
exit
ip route 0.0.0.0 0.0.0.0 10.1.1.1 CE2 interface g0/1
ip address 172.16.2.1 255.255.255.0
no shutdown
exit
interface g0/0
ip address 10.2.2.2 255.255.255.252
no shutdown
exit
ip route 0.0.0.0 0.0.0.0 10.2.2.1 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 PE1 ↔ P1 ↔ PE2 core links addressed and up 15 On PE1: show ip interface brief — Gi0/1 has 10.0.12.1 and is up/up. and On P1: show ip interface brief — Gi0/0 has 10.0.12.2 and is up/up. and On P1: show ip interface brief — Gi0/1 has 10.0.23.1 and is up/up. and On PE2: show ip interface brief — Gi0/1 has 10.0.23.2 and is up/up. 2 OSPF area 0 adjacencies formed across the core 20 On P1: show ip ospf neighbor shows at least 2 neighbour(s) in FULL. and On PE1: show ip ospf neighbor shows at least 1 neighbour(s) in FULL. and On PE2: show ip ospf neighbor shows at least 1 neighbour(s) in FULL. 3 PE1 learns PE2 loopback via OSPF 15 On PE1: show ip route lists 10.0.23.0/30. 4 iBGP session PE1 ↔ PE2 is Established 20 On PE1: show ip bgp summary — neighbour 10.0.23.2 is Established. or On PE1: show ip bgp summary — neighbour 10.0.12.2 is Established. or On PE2: show ip bgp summary — neighbour 10.0.12.1 is Established. 5 Site-A reaches Site-B end to end 30 On Site-A: ping 172.16.2.10 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
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:
PE1 interface g0/0
ip address 10.1.1.1 255.255.255.252
no shutdown
exit
interface g0/1
ip address 10.0.12.1 255.255.255.252
no shutdown
exit
router ospf 1
router-id 1.1.1.1
network 10.0.12.0 0.0.0.3 area 0
exit
router bgp 65000
bgp router-id 1.1.1.1
neighbor 10.0.23.2 remote-as 65000
network 10.1.1.0 mask 255.255.255.252
network 172.16.1.0 mask 255.255.255.0
exit
ip route 172.16.1.0 255.255.255.0 10.1.1.2 P1 interface g0/0
ip address 10.0.12.2 255.255.255.252
no shutdown
exit
interface g0/1
ip address 10.0.23.1 255.255.255.252
no shutdown
exit
router ospf 1
router-id 2.2.2.2
network 10.0.12.0 0.0.0.3 area 0
network 10.0.23.0 0.0.0.3 area 0 PE2 interface g0/0
ip address 10.2.2.1 255.255.255.252
no shutdown
exit
interface g0/1
ip address 10.0.23.2 255.255.255.252
no shutdown
exit
router ospf 1
router-id 3.3.3.3
network 10.0.23.0 0.0.0.3 area 0
exit
router bgp 65000
bgp router-id 3.3.3.3
neighbor 10.0.12.1 remote-as 65000
network 10.2.2.0 mask 255.255.255.252
network 172.16.2.0 mask 255.255.255.0
exit
ip route 172.16.2.0 255.255.255.0 10.2.2.2 P1 ip route 172.16.1.0 255.255.255.0 10.0.12.1
ip route 172.16.2.0 255.255.255.0 10.0.23.2 Where this is examined
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