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Extended ACL — publish a web server, protect everything else
Security Intermediate 4 devices 5 checked tasks 100 points Plan lab
The internet should reach one thing: the web server in the DMZ, on port 80. It should not be able to ping it, scan it, or reach the inside LAN at all — while the inside users still reach the DMZ. One extended ACL on the outside interface, inbound, in the right order. 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
The internet should reach one thing: the web server in the DMZ, on port 80. It should not be able to ping it, scan it, or reach the inside LAN at all — while the inside users still reach the DMZ. One extended ACL on the outside interface, inbound, in the right order.
Your role: a security engineer. Level: Intermediate Done when: all 5 goals show as passed (100 points).
Network status
Devices: 1 router, 2 PCs, 1 server, cabled as drawn. No Layer 1 or Layer 2 faults: every link is connected and up. Edge starts with addresses (G0/0 10.1.0.1/24, G0/1 172.16.0.1/24, G0/2 198.51.100.1/24). Inside-PC is a host with 10.1.0.10/24, gateway 10.1.0.1. DMZ-Web is a host with 172.16.0.10/24, gateway 172.16.0.1. Internet-PC is a host with 198.51.100.10/24, gateway 198.51.100.1. 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
An ACL is applied inbound on the outside interface (Gi0/2) (20 pts) The internet can fetch the web page from the DMZ server (25 pts) The internet cannot ping the DMZ server (20 pts) The internet cannot reach the inside LAN (20 pts) Inside users still reach the DMZ server (15 pts) The activity, in order
An ACL is applied inbound on the outside interface (Gi0/2) 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 internet can fetch the web page from the DMZ server Why: Each goal is a state the lab can check on the running device. Verify with: show running-config The internet cannot ping the DMZ server Why: Blocking traffic is half of security. You prove a block by showing the same ping that worked before now fails. Verify with: ping 172.16.0.10 The internet cannot reach the inside LAN Why: Blocking traffic is half of security. You prove a block by showing the same ping that worked before now fails. Verify with: ping 10.1.0.10 Inside users still reach the DMZ server Why: A ping needs a route in BOTH directions. This is the end-to-end proof that everything before it worked. Verify with: ping 172.16.0.10 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: Applying the ACL outbound on the wrong interface Common mistake: Putting “deny ip any any” first, or relying on the implicit deny without checking return traffic Common mistake: Opening a whole subnet when only a host was meant Why this matters
The internet should reach exactly one thing in your network — the published server — and only on the port it serves. An extended ACL on the outside interface, inbound, expresses that policy; the order of its lines is the policy.
What you will be able to do
Write an extended ACL that permits one service to one host and denies the rest
Apply it on the right interface in the right direction
Prove the policy from both sides: what works and what must not
The network
ISR 2911, PC, Server — 4 devices in all, already cabled.
Gi0/0 10.1.0.1/24 Fa0 Gi0/1 172.16.0.1/24 Fa0 Gi0/2 198.51.100.1/24 Fa0 Edge Inside-PC 10.1.0.10/24 · gw 10.1.0.1 DMZ-Web 172.16.0.10/24 · gw 172.16.0.1 Internet-PC 198.51.100.10/24 · gw 198.51.100.1 Drawn from this lab: devices, cables, ports and the addresses already set. Device Model Address already set
Edge ISR 2911 configure it Inside-PC PC 10.1.0.10 / 255.255.255.0 gw 10.1.0.1 DMZ-Web Server 172.16.0.10 / 255.255.255.0 gw 172.16.0.1 Internet-PC PC 198.51.100.10 / 255.255.255.0 gw 198.51.100.1
Cabling
Edge Gi0/0 ↔ Inside-PC Fa0 Edge Gi0/1 ↔ DMZ-Web Fa0 Edge Gi0/2 ↔ Internet-PC 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:
Edge interface g0/0
ip address 10.1.0.1 255.255.255.0
no shutdown
exit
interface g0/1
ip address 172.16.0.1 255.255.255.0
no shutdown
exit
interface g0/2
ip address 198.51.100.1 255.255.255.0
no shutdown
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 An ACL is applied inbound on the outside interface (Gi0/2) 20 On Edge: show running-config contains the line(s) matching interface GigabitEthernet0/2 … ip access-group \S+ in. 2 The internet can fetch the web page from the DMZ server 25 From Internet-PC, fetching http://172.16.0.10 must work (the browser, or curl http://172.16.0.10). 3 The internet cannot ping the DMZ server 20 On Internet-PC: ping 172.16.0.10 must fail — the policy blocks it. 4 The internet cannot reach the inside LAN 20 On Internet-PC: ping 10.1.0.10 must fail — the policy blocks it. 5 Inside users still reach the DMZ server 15 On Inside-PC: ping 172.16.0.10 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
Applying the ACL outbound on the wrong interface
Putting “deny ip any any” first, or relying on the implicit deny without checking return traffic
Opening a whole subnet when only a host was meant
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:
Edge access-list 110 permit tcp any host 172.16.0.10 eq 80
access-list 110 deny ip any any
interface g0/2
ip access-group 110 in
exit Where this is examined
CCNA (ACLs), CCNP ENCOR/SCOR (perimeter security), Security+ (DMZ and screened subnets), Network+ (firewall rules).
This lab practises these topics in the zNetLaB certification courses:
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