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VLSM with a WAN link 48 — 53 / 27 / 11 hosts plus a /30
Enterprise Advanced 5 devices 5 checked tasks 100 points Plan lab
Scenario — Aurangabad has Warehouse (53 hosts) and Phones (27 hosts); Chennai has Finance (11 hosts); a point-to-point link joins the routers. All of it must come out of 172.31.47.0/24. Cut right-sized subnets (largest first: /26, /27, /28, then a /30 for the link), address both routers, route between them statically and prove a PC at each site reaches the others. 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
Aurangabad has Warehouse (53 hosts) and Phones (27 hosts); Chennai has Finance (11 hosts); a point-to-point link joins the routers. All of it must come out of 172.31.47.0/24. Cut right-sized subnets (largest first: /26, /27, /28, then a /30 for the link), address both routers, route between them statically and prove a PC at each site reaches the others.
Your role: a network engineer on the enterprise team. Level: Advanced Done when: all 5 goals show as passed (100 points).
Network status
Devices: 2 routers, 3 PCs, cabled as drawn. No Layer 1 or Layer 2 faults: every link is connected and up. Warehouse (53) is a host with 172.31.47.2/26, gateway 172.31.47.1. Phones (27) is a host with 172.31.47.66/27, gateway 172.31.47.65. Finance (11) is a host with 172.31.47.98/28, gateway 172.31.47.97. R-Aurangabad, R-Chennai start with an empty configuration. 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
Aurangabad: Gi0/0 = 172.31.47.1/26 (Warehouse) and Gi0/2 = 172.31.47.65/27 (Phones) (20 pts) Chennai: Gi0/0 = 172.31.47.97/28 (Finance) (15 pts) The WAN link is a /30: 172.31.47.113 ⇄ 172.31.47.114 (20 pts) Each router has static routes to the networks at the far site (20 pts) A PC at Aurangabad reaches the PC at Chennai, and the reverse (25 pts) The activity, in order
Aurangabad: Gi0/0 = 172.31.47.1/26 (Warehouse) and Gi0/2 = 172.31.47.65/27 (Phones) 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 Chennai: Gi0/0 = 172.31.47.97/28 (Finance) 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 The WAN link is a /30: 172.31.47.113 ⇄ 172.31.47.114 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 Each router has static routes to the networks at the far site 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 A PC at Aurangabad reaches the PC at Chennai, and the reverse Why: A ping needs a route in BOTH directions. This is the end-to-end proof that everything before it worked. Verify with: ping 172.31.47.98 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: Allocating the WAN /30 first and misaligning the big subnets Common mistake: Counting the network and broadcast addresses as hosts Common mistake: Forgetting a route on one side Why this matters
Real designs mix LANs of different sizes and point-to-point links in the same block. Allocate the biggest subnet first so blocks stay aligned, give links a /30, and then the routers need routes to the subnets they do not touch.
What you will be able to do
Allocate LAN subnets and a /30 link from one block
Address two routers from the plan
Route between the sites
The network
ISR 2911, PC — 5 devices in all, already cabled.
Fa0 Gi0/0 Fa0 Gi0/2 Gi0/1 Gi0/1 Fa0 Gi0/0 R-Aurangabad R-Chennai Warehouse (53) 172.31.47.2/26 · gw 172.31.47.1 Phones (27) 172.31.47.66/27 · gw 172.31.47.65 Finance (11) 172.31.47.98/28 · gw 172.31.47.97 Drawn from this lab: devices, cables, ports and the addresses already set. Device Model Address already set
R-Aurangabad ISR 2911 configure it R-Chennai ISR 2911 configure it Warehouse (53) PC 172.31.47.2 / 255.255.255.192 gw 172.31.47.1 Phones (27) PC 172.31.47.66 / 255.255.255.224 gw 172.31.47.65 Finance (11) PC 172.31.47.98 / 255.255.255.240 gw 172.31.47.97
Cabling
Warehouse (53) Fa0 ↔ R-Aurangabad Gi0/0 Phones (27) Fa0 ↔ R-Aurangabad Gi0/2 R-Aurangabad Gi0/1 ↔ R-Chennai Gi0/1 Finance (11) Fa0 ↔ R-Chennai Gi0/0
What is configured at the start
Nothing is configured to start with beyond the addresses above: you build the configuration from a clean start.
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 Aurangabad: Gi0/0 = 172.31.47.1/26 (Warehouse) and Gi0/2 = 172.31.47.65/27 (Phones) 20 On R-Aurangabad: show ip interface brief — Gi0/0 has 172.31.47.1 and is up/up. and On R-Aurangabad: show ip interface brief — Gi0/2 has 172.31.47.65 and is up/up. 2 Chennai: Gi0/0 = 172.31.47.97/28 (Finance) 15 On R-Chennai: show ip interface brief — Gi0/0 has 172.31.47.97 and is up/up. 3 The WAN link is a /30: 172.31.47.113 ⇄ 172.31.47.114 20 On R-Aurangabad: show ip interface brief — Gi0/1 has 172.31.47.113 and is up/up. and On R-Chennai: show ip interface brief — Gi0/1 has 172.31.47.114 and is up/up. 4 Each router has static routes to the networks at the far site 20 On R-Aurangabad: show ip route lists 172.31.47.96/28. and On R-Chennai: show ip route lists 172.31.47.0/26. and On R-Chennai: show ip route lists 172.31.47.64/27. 5 A PC at Aurangabad reaches the PC at Chennai, and the reverse 25 On Warehouse (53): ping 172.31.47.98 must succeed. and On Finance (11): ping 172.31.47.66 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
Allocating the WAN /30 first and misaligning the big subnets
Counting the network and broadcast addresses as hosts
Forgetting a route on one side
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-Aurangabad interface g0/0
ip address 172.31.47.1 255.255.255.192
no shutdown
exit
interface g0/2
ip address 172.31.47.65 255.255.255.224
no shutdown
exit
interface g0/1
ip address 172.31.47.113 255.255.255.252
no shutdown
exit
ip route 172.31.47.96 255.255.255.240 172.31.47.114 R-Chennai interface g0/0
ip address 172.31.47.97 255.255.255.240
no shutdown
exit
interface g0/1
ip address 172.31.47.114 255.255.255.252
no shutdown
exit
ip route 172.31.47.0 255.255.255.192 172.31.47.113
ip route 172.31.47.64 255.255.255.224 172.31.47.113 Where this is examined
CCNA 1.0 IPv4 addressing; CCNA 3.0 static routing.
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