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Troubleshoot — it works by address and fails by name
Enterprise Beginner 4 devices 3 checked tasks 100 points Free lab
“The website is down.” Pinging the server by its address works; by its name fails. Name resolution is a separate step from reachability — ask which DNS server the PC is using and whether that server has the record. 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 is a free lab: it stays open on the free plan. It needs an account, which keeps your progress.
The scenario
“The website is down.” Pinging the server by its address works; by its name fails. Name resolution is a separate step from reachability — ask which DNS server the PC is using and whether that server has the record.
Your role: a network engineer on the enterprise team. Level: Beginner Done when: all 3 goals show as passed (100 points).
Network status
Devices: 1 switch, 1 PC, 2 servers, cabled as drawn. No Layer 1 or Layer 2 faults: every link is connected and up. PC1 is a host with 10.0.0.11/24, gateway 10.0.0.1. DNS is a host with 10.0.0.53/24, gateway 10.0.0.1. Web is a host with 10.0.0.80/24, gateway 10.0.0.1. SW1 starts with an empty configuration. 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
PC1 asks the DNS server that holds the record (10.0.0.53) (40 pts) PC1 resolves www.znetlab.lab (30 pts) PC1 opens the site by name (30 pts) The activity, in order
PC1 asks the DNS server that holds the record (10.0.0.53) Why: Reading a show command is the core skill of troubleshooting: the output is the truth, not your configuration. Verify with: ipconfig /all PC1 resolves www.znetlab.lab Why: Each goal is a state the lab can check on the running device. Verify with: show running-config PC1 opens the site by name Why: Each goal is a state the lab can check on the running device. Verify with: show running-config 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: Restarting the web server for a DNS problem Common mistake: Editing the hosts file as a “fix” Common mistake: Pointing every client at a different DNS server instead of fixing the DHCP option Why this matters
Name resolution is a separate step from reachability. “The site is down” often means the PC asks a DNS server that does not know the name. Ping by address first, then by name, and the failing step is obvious.
What you will be able to do
Separate reachability from name resolution
Read the DNS server a host is using (ipconfig /all)
Fix the client’s DNS setting and test by name
The network
Catalyst 2960-24TT, PC, Server — 4 devices in all, already cabled.
Fa0/1 Fa0 Fa0/2 Fa0 Fa0/3 Fa0 SW1 PC1 10.0.0.11/24 · gw 10.0.0.1 DNS 10.0.0.53/24 · gw 10.0.0.1 Web 10.0.0.80/24 · gw 10.0.0.1 Drawn from this lab: devices, cables, ports and the addresses already set. Device Model Address already set
SW1 Catalyst 2960-24TT configure it PC1 PC 10.0.0.11 / 255.255.255.0 gw 10.0.0.1 DNS Server 10.0.0.53 / 255.255.255.0 gw 10.0.0.1 Web Server 10.0.0.80 / 255.255.255.0 gw 10.0.0.1
Cabling
SW1 Fa0/1 ↔ PC1 Fa0 SW1 Fa0/2 ↔ DNS Fa0 SW1 Fa0/3 ↔ Web Fa0
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 PC1 asks the DNS server that holds the record (10.0.0.53) 40 On PC1: ipconfig /all output matches DNS Servers[ .]*: 10\.0\.0\.53. 2 PC1 resolves www.znetlab.lab 30 On PC1: nslookup www.znetlab.lab resolves. 3 PC1 opens the site by name 30 From PC1, fetching www.znetlab.lab must work (the browser, or curl www.znetlab.lab).
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
Restarting the web server for a DNS problem
Editing the hosts file as a “fix”
Pointing every client at a different DNS server instead of fixing the DHCP option
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:
PC1 netsh interface ip set address "Ethernet" static 10.0.0.11 255.255.255.0 10.0.0.1
netsh interface ip set dns "Ethernet" static 10.0.0.53 Where this is examined
Network+ (DNS troubleshooting), CCNA (IP services).
This lab practises these topics in the zNetLaB certification courses:
DHCP, DNS, NTP, SNMP, Syslog — CCNA · IP Services Troubleshooting DHCP, NAT, SNMP, syslog, IP SLA, NetFlow — CCNP Enterprise · ENARSI · Infrastructure Services Service problems: DNS, DHCP, NAT, ACLs — CompTIA Network+ · Network Troubleshooting
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