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NAT overload 13 — Patna to the internet
Enterprise Intermediate 3 devices 4 checked tasks 100 points Plan lab
The Patna LAN uses private 192.168.32.0/24. The ISP (198.51.32.2) will not route it, so translate every inside host to the router’s one outside address (PAT), add a default route, and ping the ISP’s test address 8.8.32.8. 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 Patna LAN uses private 192.168.32.0/24. The ISP (198.51.32.2) will not route it, so translate every inside host to the router’s one outside address (PAT), add a default route, and ping the ISP’s test address 8.8.32.8.
Your role: a network engineer on the enterprise team. Level: Intermediate Done when: all 4 goals show as passed (100 points).
Network status
Devices: 2 routers, 1 PC, cabled as drawn. No Layer 1 or Layer 2 faults: every link is connected and up. Edge-Patna starts with addresses (G0/0 192.168.32.1/24, G0/1 198.51.32.1/30). ISP-Rajkot starts with addresses (G0/1 198.51.32.2/30, L0 8.8.32.8/32). Inside-PC is a host with 192.168.32.10/24, gateway 192.168.32.1. 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
Gi0/0 is the inside and Gi0/1 the outside interface (20 pts) Inside hosts are translated with overload (25 pts) A default route points to the ISP (15 pts) The inside PC reaches 8.8.32.8 (40 pts) The activity, in order
Gi0/0 is the inside and Gi0/1 the outside interface 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 Inside hosts are translated with overload Why: PAT lets many private hosts share one public address; the ports tell the replies apart. Verify with: show ip nat translations A default route points to the ISP Why: The next hop must be an address on a directly connected subnet, or the route never enters the table. Verify with: show ip route The inside PC reaches 8.8.32.8 Why: A ping needs a route in BOTH directions. This is the end-to-end proof that everything before it worked. Verify with: ping 8.8.32.8 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: Swapping inside and outside Common mistake: An ACL that does not match the inside subnet Common mistake: No default route — translation works but the packet goes nowhere Why this matters
Private addresses are not routed on the internet. NAT overload (PAT) rewrites every inside source to the router’s one public address and tells the connections apart by port number, so a whole LAN shares one address.
What you will be able to do
Mark inside and outside interfaces
Write the ACL that selects what to translate
Configure PAT and a default route
Verify with show ip nat translations
The network
ISR 2911, PC — 3 devices in all, already cabled.
Fa0 Gi0/0 192.168.32.1/24 Gi0/1 198.51.32.1/30 Gi0/1 198.51.32.2/30 Edge-Patna ISP-Rajkot Inside-PC 192.168.32.10/24 · gw 192.168.32.1 Drawn from this lab: devices, cables, ports and the addresses already set. Device Model Address already set
Edge-Patna ISR 2911 configure it ISP-Rajkot ISR 2911 configure it Inside-PC PC 192.168.32.10 / 255.255.255.0 gw 192.168.32.1
Cabling
Inside-PC Fa0 ↔ Edge-Patna Gi0/0 Edge-Patna Gi0/1 ↔ ISP-Rajkot 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:
Edge-Patna interface g0/0
ip address 192.168.32.1 255.255.255.0
no shutdown
exit
interface g0/1
ip address 198.51.32.1 255.255.255.252
no shutdown
exit ISP-Rajkot interface g0/1
ip address 198.51.32.2 255.255.255.252
no shutdown
exit
interface lo0
ip address 8.8.32.8 255.255.255.255
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 Gi0/0 is the inside and Gi0/1 the outside interface 20 On Edge-Patna: show running-config contains the line(s) matching interface GigabitEthernet0/0 … ip nat inside. and On Edge-Patna: show running-config contains the line(s) matching interface GigabitEthernet0/1 … ip nat outside. 2 Inside hosts are translated with overload 25 On Edge-Patna: show running-config | include nat shows overload . 3 A default route points to the ISP 15 On Edge-Patna: show ip route 0.0.0.0 shows next hop 198.51.32.2. 4 The inside PC reaches 8.8.32.8 40 On Inside-PC: ping 8.8.32.8 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
Swapping inside and outside
An ACL that does not match the inside subnet
No default route — translation works but the packet goes nowhere
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-Patna access-list 1 permit 192.168.32.0 0.0.0.255
interface g0/0
ip nat inside
exit
interface g0/1
ip nat outside
exit
ip nat inside source list 1 interface g0/1 overload
ip route 0.0.0.0 0.0.0.0 198.51.32.2 Where this is examined
CCNA 4.0 IP Services (NAT/PAT).
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