1. What is the difference between a modem and a router?

A modem connects your home to the internet via your ISP. A router connects your devices (like
phone, laptop, TV) to the modem and allows them to talk to each other and share the internet. A
modem is the device that communicates with the ISP and brings internet to your location. A router,
on the other hand, creates a local network inside the home and distributes that internet to multiple
devices wirelessly or via LAN cables. In many cases, it’s a combo device—modem and router in one.
If there's a connectivity issue, it's important to isolate whether the modem is not getting internet or
the router is not distributing it properly.

2. What would you check if a customer says “I have no internet”?

First, I would ask if the router’s internet LED is on. If it’s off or red, I’d ask them to power cycle the
router and modem—turn it off, wait 30 seconds, and turn it back on. Then I’d check if the issue is
with just one device or all. If it’s one device, it could be a device-specific problem like Wi-Fi adapter
or IP conflict. If all devices have no internet, it could be an ISP issue or modem failure. I’d also guide
them to test using an Ethernet cable to bypass Wi-Fi issues.

Step 1: Ask them to:

• Turn off the modem/router.

• Wait 30 seconds.

• Turn them back on.

• Wait 2–3 minutes and check the connection again.

Step 2: Check Physical Connections Ask:

• “Are the Ethernet cables securely connected?”

• “Do you see the usual lights on the modem/router?”

Step 3: Check Device Settings If only one device has no internet:

• Ask them to forget and reconnect to Wi-Fi.

• Check if they see “Connected, No Internet.” This indicates network is detected but not working.

• Try using ipconfig /release and ipconfig /renew (if using Windows). Restart the router.

Step 4: Ping Test: If no reply, there’s likely no internet or DNS/network issue.

3. What is an IP address and why is it important?

It’s a unique ID for a device on a network. An IP address is like a digital home address for a device.
Every device needs one to send and receive data on a network. Without an IP, your device doesn’t
know where to send or get information. There are two main types—private IPs used inside the
home, and public IPs used by ISPs to identify your connection on the internet.

4. How would you troubleshoot slow internet?

First, I’d ask the customer to check if it’s slow on all devices or just one. If all are affected, I’d check
how many devices are connected—maybe bandwidth is overused. Then I’d guide them to run a
speed test and compare it with the subscribed plan. I'd also suggest restarting the router, checking
signal strength, switching to a different channel or frequency band (2.4GHz vs 5GHz), and checking
for firmware updates.
5. What tools/commands would you use to troubleshoot connectivity?
I’d use basic commands like:

• ipconfig – to check IP and gateway.

• ping – to test connection to server or gateway.

• tracert – to trace the route to a website.

• nslookup – to check DNS resolution.

These help identify whether it’s a local issue, DNS issue, or ISP-related.

6. How do you check if it's a DNS problem?

If a customer says websites aren’t loading, I’d try to ping a domain name like ping google.com. If that
fails, I’d try pinging the IP address like ping 8.8.8.8. If IP works but domain doesn’t, it’s likely a DNS
issue. I’d then suggest changing DNS to Google’s public DNS (8.8.8.8, 8.8.4.4) and testing again.

7. What is the OSI Model? Can you explain its layers?

It’s a framework for how data travels over a network. The OSI model is a 7-layer model that helps
understand how data moves in a network. Each layer has a specific function:

• Layer 1 (Physical): Cables, switches, signal transmission.

• Layer 2 (Data Link): MAC addresses, Ethernet.

• Layer 3 (Network): IP addresses, routing.

• Layer 4 (Transport): TCP/UDP, ports.

• Layer 5–7: Session, Presentation, Application—where software and user interaction happen. In
troubleshooting, we mostly focus on the first 4 layers.

8. What’s the difference between TCP and UDP?

TCP is connection-oriented and ensures reliable data transfer—like for emails or file downloads. UDP
is connectionless, faster, but doesn’t guarantee delivery—used in video streaming or VoIP. For
example, if a call drops or voice breaks in a support call, it might be UDP packet loss.

9. A customer says “Wi-Fi disconnects every few minutes.” What do you check?
I’d first ask if it happens on all devices. If yes, I'd check router placement and interference (from
walls, microwaves). Then I’d check if the router firmware is up to date. Also, I'd advise switching
from 2.4GHz to 5GHz if supported or changing the Wi-Fi channel. If it’s only one device, it could be a
driver or power-saving setting.

10. What is DNS and DHCP and how does it work?

DNS (Domain Name System) converts website names (like google.com) into IP addresses that
computers use to find each other. Makes websites accessible with names instead of numbers.
Browsers save DNS responses temporarily, speeding up repeated visits to websites. DNS can direct
users to the nearest or least-busy server for better performance.

DHCP (Dynamic Host Configuration Protocol) automatically assigns IP addresses to devices on a

network. When a device connects, the DHCP server (usually the router) gives it an IP, gateway, and
DNS info. This avoids manual configuration. If it fails, the device might show a 169.x.x.x IP—which
means it couldn’t get an IP.
11. What is NAT and why is it used?
NAT (Network Address Translation) lets multiple devices share one public IP to access the internet.
It’s used in home routers. Internally, devices have private IPs (like 192.168.x.x), but NAT maps them
to the single public IP when accessing the internet. This saves IP addresses and adds security. You
don’t have to request or assign a public IP to every device. Reduces admin overhead for network
managers.

12. How do you reset a router?

First, try a soft reset—power off, wait 30 seconds, and power back on. If issues persist, press and
hold the reset button (usually a pinhole) for 10–15 seconds. This does a factory reset, clearing all
settings including Wi-Fi name/password. Then reconfigure using the admin panel (192.168.1.1 or
similar).

13. How do you check if it's an ISP outage?

If all lights are fine but there's no internet, I’d ask if the customer has another device (like mobile
with hotspot) to check ISP’s status page or social media. Some routers show “WAN disconnected” or
“No DSL signal” which confirms ISP issue. I’d also ping a public IP like 8.8.8.8—if that fails, it’s likely
an outage.

14. What’s the difference between static and dynamic IP?

A static IP stays fixed—it’s manually configured and doesn’t change. A dynamic IP is automatically
assigned by DHCP and can change after a restart. Static IPs are used in servers or printers. Dynamic is
common in home users.

Static IP – Key Benefits:

• Easy to host websites or servers.

• Useful for remote access (like CCTV).

• Always reachable with the same IP.

Dynamic IP – Key Benefits:

• More secure (harder to track).

• Automatic setup – no technical knowledge needed.

• Saves IP space by reusing addresses.

15. What is MAC address and how is it different from IP?

MAC address is a hardware ID, unique to every device’s network card. It never changes. IP address is
assigned by the network, and it can change (dynamic). MAC is used at Layer 2, while IP is Layer 3 in
OSI. IP addresses can change (dynamic), but MAC addresses remain permanently assigned to
hardware. Network admins can allow or block devices based on their MAC address. It helps IT
support teams trace issues to specific devices and resolve it quickly.

16. What is ping and how do you use it?

Ping checks if your device can reach another device/server. If successful, it shows response time. If it
fails (timeout or unreachable), there’s a network problem. It helps isolate issues—e.g., pinging
127.0.0.1 tests local adapter, pinging router IP tests LAN, and pinging 8.8.8.8 tests internet access.
17. How do you troubleshoot a computer with “No Internet Access” warning?
I'd check:

1. Is the device connected to Wi-Fi?

2. Run ipconfig to see if it has a valid IP.

3. Try renewing IP using ipconfig /release and ipconfig /renew.

4. Restart the adapter.

5. Test using LAN cable.

6. Restart the router/modem.

18. What causes “Limited or No Connectivity” on Wi-Fi?

It usually means the device got connected to the router, but didn’t get internet access. Causes
include:

• DHCP failure.

• Router not connected to internet.

• IP conflict.

• DNS issues.

19. How do you log in to a router and what can you check there?
Open browser → type 192.168.1.1 or 192.168.0.1 → login with default creds (admin/admin). Inside,
you can check:

• Connected devices.

• Signal strength.

• Wi-Fi settings.

• Firmware version.

• WAN status (if it shows disconnected, it's an ISP issue).

20. What’s the first thing you do when a customer says “My internet is not working”?
I’d calmly verify if it’s a complete outage or device-specific. Then check router/modem lights, ask
them to reboot devices, check Wi-Fi name and signal. If needed, guide them to test via LAN or log in
to the router. Based on clues, isolate whether it’s a device issue, router issue, or ISP problem.

21. What is “ipconfig”?

ipconfig is a Windows command used to view and manage network settings. It shows info like: IP
address, Subnet mask (Defines the network portion of an IP address.), Default gateway (The router
that connects your device to other networks, like the internet.).

You can also use it with switches like:

• ipconfig /release → disconnect IP

• ipconfig /renew → request new IP

• ipconfig /flushdns → clear DNS cache

22. Define DNS Flushing.
Flushing DNS clears outdated or corrupted DNS records from your computer's cache. It helps fix
issues like websites not loading, wrong site opening, or DNS errors by forcing your system to get
fresh DNS info from the server.

23. Define “tracert” and “nslookup”.

tracert (short for trace route) is a Windows command that shows the path your data takes to reach a
destination over the internet. It lists each hop (router) between your device and the target IP or
website, along with how long it takes to reach each one. Helpful for diagnosing network delays or
connection problems, like finding where the slowdown is happening.

nslookup (Name Server Lookup) is a command used to find the IP address of a domain name or vice
versa. Typing nslookup google.com will show you the IP address(es) of Google. Use case: Helps
troubleshoot DNS-related issues, like checking if a domain resolves correctly.

24. How to resolve DNS related issue?

DNS issues occur when your computer can’t convert domain names (like google.com) into IP
addresses, which prevents websites from loading.
Common Symptoms:

• Websites not opening

• “DNS server not responding” error

• Internet works with IP address but not domain name

To resolve DNS-related issues, follow these steps:

1. Flush the DNS Cache

ipconfig /flushdns

Clears old or corrupt DNS records from your computer.

2. Change DNS Server Manually

Go to:

• Control Panel > Network & Internet > Network Connections

• Right-click your connection → Properties

• Select IPv4 → Click Properties

• Use a reliable DNS like: Google DNS: 8.8.8.8 and 8.8.4.4

Cloudflare DNS: 1.1.1.1

3. Restart Router

This resets your connection and may assign fresh DNS info from ISP.

* Disable VPN or Proxy (if used)

These can interfere with DNS resolution.
Bonus Tip: If the issue is only with one site, try opening it on another device or network to confirm
it’s DNS-related.
25. What is DHCP failure and how would you resolve this issue?
A DHCP failure means your device couldn’t get an IP address from the DHCP server (usually the
router), so it can't connect to the network or internet.
Common Causes:

• Router/DHCP server is down or unresponsive

• Network cable is unplugged or Wi-Fi is unstable

• Too many devices connected (IP pool exhausted)

• Firewall or antivirus blocking the DHCP response

How to Fix It:

1. Restart your router and computer (resets the DHCP process)

2. Use ipconfig /release and ipconfig /renew (renews your IP lease)

3. Check network adapter settings o Make sure it’s set to Obtain IP address automatically

4. Temporarily assign a static IP o Go to IPv4 settings and manually enter an IP, subnet, and gateway

If DHCP fails, the device may show an IP like 169.254.x.x, which means it assigned itself a local IP—
no internet.

26. What is an IP Conflict?

An IP conflict happens when two devices on the same network are assigned the same IP address,
which causes both to lose or have unstable connectivity.
Common Causes:

• Manual/static IPs assigned to multiple devices

• DHCP server misconfiguration

• Device reconnecting too quickly before DHCP refresh

How to Fix:

1. Restart the affected devices (forces them to request a new IP)

2. Use ipconfig /release and ipconfig /renew (resolves IP assignment issues)

3. Check for static IP settings o Set to Obtain IP automatically unless a static IP is needed

4. Reboot the router (refreshes the DHCP IP pool)

27. How to Update Router Firmware?
Step 1: Connect to the Router: Use a wired Ethernet connection (recommended for stability), or
connect via Wi-Fi.

Step 2: Find Your Router’s IP Address

You can check this on a PC:
Open Command Prompt.
Type: ipconfig
Look for Default Gateway – that's your router's IP.

Step 3: Log in to Router's Web Interface

Open a web browser.
Enter the router’s IP address in the address bar.
Enter your admin username and password (often printed on the router or provided by the ISP).

Step 4: Locate Firmware Update Section

Look for something like "Firmware Upgrade" or "Router Update."

Step 5: Check for New Firmware

Many modern routers have an option to automatically check for updates online.
Click Check, then follow the prompts to Download and Install.

Step 7: Wait and Reboot

The update may take several minutes.
The router will usually reboot automatically.
Once done, reconnect and verify if the new firmware version is shown.

28. What is VoIP and how does it work?

VoIP (Voice over Internet Protocol) is a technology that allows voice calls to be made using an
internet connection instead of traditional telephone lines. It converts voice signals into digital
packets, sends them over the internet, and reconverts them at the receiver's end. VoIP relies on
sufficient bandwidth and low latency for clear communication.

29. What could cause poor VoIP call quality (like echo, delay, or voice drop)?
High latency – causes delay in voice transmission.

Jitter – inconsistent packet arrival leads to voice distortion.

Packet loss – causes missing audio segments or dropped calls.

Low bandwidth – leads to choppy audio or call drops.

Wireless interference or too many devices on the network can also affect quality.

30. How would you troubleshoot a customer complaint of “My VoIP calls keep dropping”?
1. Check if the internet connection is stable.

2. Ask the customer to test a speed test and note ping, jitter, and packet loss.

3. Recommend using a wired (Ethernet) connection instead of Wi-Fi.

4. Power cycle modem/router and VoIP device (if separate).

 31. What is SIP and how is it related to VoIP?
SIP (Session Initiation Protocol) is a signaling protocol used to establish, modify, and terminate VoIP
calls. While VoIP is the general technology, SIP is one of the most common protocols used in its
implementation, especially for business and residential VoIP services.

32. What ports are commonly used by VoIP services?

VoIP typically uses:

SIP signaling – UDP/TCP port 5060 or 5061 (secure SIP).

RTP (Real-time Transport Protocol) – dynamic range 10000–20000+ for voice packets.

If these ports are blocked by a firewall or not properly forwarded, calls may not go through or audio
may be missing.

What is IoT (Internet of Things)?

IoT stands for Internet of Things — it refers to smart devices like smart TVs, smart bulbs, smart thermostats,
or security cameras that are connected to the internet to collect or share data.

What are the most common reasons IoT devices fail to connect?
Wi-Fi signal is too weak
Wrong password or SSID
Device only supports 2.4 GHz and router is set to 5 GHz only
MAC filtering is enabled on the router
Device needs a firmware update