MikroTik MTCNA lab 17 of 19
Troubleshooting: the office has no Internet
A small-office router built by someone else doesn't work: PCs get no addresses, then no Internet, then no names. Work bottom-up with RouterOS tools to find six realistic faults, fix each one and record what you found.
Run this lab
It needs Lite: its 5 nodes are set to 5 vCPU and 3,072 MB in total. That fits the free demo too.
In your workspace: Shared, then MikroTik MTCNA RouterOS v7 guided labs, then 17 - Troubleshooting - the office has no Internet
- Level
- Intermediate
- Time
- About 60 minutes
- Nodes need
- 5 vCPU, 3,072 MB
- Smallest plan
- Lite
The scenario
A dental practice's previous IT company set up its MikroTik and then went out of business. On Monday morning nobody can work: "the Internet is down". The provider (ISP) says the line is fine and the router has a lease. You have the router's console, two PCs, and the practice manager's Laptop (Linux). Find and fix everything that is wrong, and write down what you found for the practice's records.
How it should work: the WAN (ether1) gets its address, default route and DNS from the provider by DHCP; the LAN bridge (ether2, ether3) is 192.168.88.1/24 and hands out DHCP addresses with gateway and DNS 192.168.88.1; LAN traffic is masqueraded to the WAN; the router answers DNS for the LAN; the firewall protects the router and the LAN.
| Device | Interface | Expected |
|---|---|---|
| GW | ether1 | DHCP client, 203.0.113.x/24, default route to 203.0.113.1 |
| GW | bridge-lan | 192.168.88.1/24, DHCP server dhcp-lan |
| PC1, PC2 | eth0 | DHCP |
| Laptop | eth0 | DHCP (root, no password) |
| Internet | www.fernvale.example | 198.51.100.10 |
What you’ll practise
- Troubleshoot methodically from the client up: address, gateway, routing, NAT, firewall, DNS
- Spot an invalid DHCP server and a wrong DHCP network setting
- Read DHCP client options that decide the default route
- Use firewall counters and NAT counters to find where packets stop
- Fix DNS for LAN clients
- Document faults as symptom, evidence, cause and fix
The tasks
- Get the PCs an address
- Check what the PCs were told
- Can the router itself reach the Internet?
- Why can't the PCs get out?
- Names don't resolve
- Write it up
The Lab Tasks pane has the scenario, these tasks, the checks to run, hints and the full solution.
Topology and devices
The network as it opens in EVE-NG, drawn from the lab’s own canvas, and the image each node runs.
Every link, as text
- ISP
ether1to GWether1 - GW
ether2to Office-LAN (network) - PC1
eth0to Office-LAN (network) - PC2
eth0to Office-LAN (network) - Laptop
eth0to Office-LAN (network)
| Node | Device | Image in Add Node | Set to |
|---|---|---|---|
| ISP | MikroTik RouterOS | mikrotik-7.14.2 | 1 vCPU, 256 MB |
| GW | MikroTik RouterOS | mikrotik-7.14.2 | 1 vCPU, 256 MB |
| PC1 | VPCS host | Built in to EVE-NG | Counted as 1 vCPU, 1,024 MB |
| PC2 | VPCS host | Built in to EVE-NG | Counted as 1 vCPU, 1,024 MB |
| Laptop | Alpine Linux | clbalpinebase-alpine-base-3-20-3 | 1 vCPU, 512 MB |
How to open this lab
Sign in to your workspace at
lab.cloudlabbox.com.In File Manager, open Shared, then the folder
MikroTik MTCNA RouterOS v7 guided labs.Open
17 - Troubleshooting - the office has no Internetand start its nodes, then open Lab Tasks for the scenario and the steps.
The lab is read-only. You can start the nodes and configure the devices, but changes to the topology can’t be saved. To change it, rebuild it in your own folder.
More MikroTik MTCNA labs
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CloudLabBox is independent of MikroTik. The lab follows exam topics and isn’t vendor training material; vendor names identify the exams and the images in the workspace.