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Extended ACL 38 — stop host .12's ping, leave everything else
Security Intermediate 5 devices 4 checked tasks 100 points Plan lab
Scenario — the Admin server in Mangaluru (10.57.2.10) is being scanned with ping from the PC at 10.57.1.12. Write extended ACL 137 that denies ICMP from that one host to the server and permits all other traffic, and apply it inbound on the LAN-facing port (Gi0/0) — an extended ACL goes close to the source. The other PC must still reach the server. 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 Admin server in Mangaluru (10.57.2.10) is being scanned with ping from the PC at 10.57.1.12. Write extended ACL 137 that denies ICMP from that one host to the server and permits all other traffic, and apply it inbound on the LAN-facing port (Gi0/0) — an extended ACL goes close to the source. The other PC must still reach the server.
Your role: a security engineer. Level: Intermediate Done when: all 4 goals show as passed (100 points).
Network status
Devices: 1 router, 1 switch, 3 PCs, cabled as drawn. No Layer 1 or Layer 2 faults: every link is connected and up. R-Mangaluru starts with addresses (G0/0 10.57.1.1/24, G0/1 10.57.2.1/24). Host-11 is a host with 10.57.1.11/24, gateway 10.57.1.1. Host-12 is a host with 10.57.1.12/24, gateway 10.57.1.1. Admin-Server is a host with 10.57.2.10/24, gateway 10.57.2.1. SW-Mangaluru starts 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
ACL 137 denies ICMP from host 10.57.1.12 to the server, then permits IP (30 pts) It is applied inbound on Gi0/0 (near the source) (20 pts) Host .12 can no longer ping the server (25 pts) Host .11 still can (25 pts) The activity, in order
ACL 137 denies ICMP from host 10.57.1.12 to the server, then permits IP 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 It is applied inbound on Gi0/0 (near the source) 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 Host .12 can no longer ping the 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 10.57.2.10 Host .11 still can Why: A ping needs a route in BOTH directions. This is the end-to-end proof that everything before it worked. Verify with: ping 10.57.2.10 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: Placing an extended ACL near the destination Common mistake: Forgetting permit ip any any Common mistake: Reversing source and destination Why this matters
An extended ACL can match protocol, source and destination, so it is placed near the source: the unwanted packet dies before it crosses the network. The invisible deny-all at the end means a permit ip any any is needed for everything you did not name.
What you will be able to do
Write an extended ACL with protocol, source and destination
Place it near the source in the right direction
Prove one host is blocked and another is not
The network
ISR 2911, Catalyst 2960-24TT, PC — 5 devices in all, already cabled.
Gi0/1 Gi0/0 10.57.1.1/24 Fa0/1 Fa0 Fa0/2 Fa0 Fa0 Gi0/1 10.57.2.1/24 R-Mangaluru SW-Mangaluru Host-11 10.57.1.11/24 · gw 10.57.1.1 Host-12 10.57.1.12/24 · gw 10.57.1.1 Admin-Server 10.57.2.10/24 · gw 10.57.2.1 Drawn from this lab: devices, cables, ports and the addresses already set. Device Model Address already set
R-Mangaluru ISR 2911 configure it SW-Mangaluru Catalyst 2960-24TT configure it Host-11 PC 10.57.1.11 / 255.255.255.0 gw 10.57.1.1 Host-12 PC 10.57.1.12 / 255.255.255.0 gw 10.57.1.1 Admin-Server PC 10.57.2.10 / 255.255.255.0 gw 10.57.2.1
Cabling
SW-Mangaluru Gi0/1 ↔ R-Mangaluru Gi0/0 SW-Mangaluru Fa0/1 ↔ Host-11 Fa0 SW-Mangaluru Fa0/2 ↔ Host-12 Fa0 Admin-Server Fa0 ↔ R-Mangaluru 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-Mangaluru interface g0/0
ip address 10.57.1.1 255.255.255.0
no shutdown
exit
interface g0/1
ip address 10.57.2.1 255.255.255.0
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 ACL 137 denies ICMP from host 10.57.1.12 to the server, then permits IP 30 On R-Mangaluru: show running-config contains the line(s) matching access-list 137 deny icmp host 10\.57\.1\.12 host 10\.57\.2\.10[\s\S]*access-list 137 permit ip any any. 2 It is applied inbound on Gi0/0 (near the source) 20 On R-Mangaluru: show running-config contains the line(s) matching interface GigabitEthernet0/0 … ip access-group 137 in. 3 Host .12 can no longer ping the server 25 On Host-12: ping 10.57.2.10 must fail — the policy blocks it. 4 Host .11 still can 25 On Host-11: ping 10.57.2.10 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
Common mistakes
Placing an extended ACL near the destination
Forgetting permit ip any any
Reversing source and destination
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-Mangaluru access-list 137 deny icmp host 10.57.1.12 host 10.57.2.10
access-list 137 permit ip any any
interface g0/0
ip access-group 137 in
exit Where this is examined
CCNA 5.6 ACLs; Security+ 3.2.
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