🧭 1. Understanding DNS, DHCP, and Firewall
DNS (Domain Name System)
- Translates domain names (e.g., www.google.com)
into IP addresses (e.g., 142.250.190.14).
- Without DNS, you’d have to
remember every site’s IP address manually.
Common
DNS Symptoms:
- “DNS server not responding”
- Websites fail to load, but
pinging IPs works
- Very slow website loading
DHCP (Dynamic Host Configuration Protocol)
- Automatically assigns IP
addresses to devices on your network.
- Prevents IP conflicts and
ensures smooth network connectivity.
Common
DHCP Symptoms:
- “Limited or no connectivity”
- IP address starts with 169.x.x.x
(means device didn’t get an IP from DHCP server)
- Devices can connect to Wi-Fi
but have no internet
Firewall
- Controls incoming and outgoing
network traffic based on predefined rules.
- Protects against unauthorized
access and malware.
Common
Firewall Symptoms:
- Certain websites, applications,
or games won’t connect
- Network discovery disabled
- “Access denied” or “Connection
blocked” messages
⚙️ 2. Common Causes of Issues
|
Component |
Causes |
|
DNS |
Wrong server settings, ISP DNS
outage, corrupted cache, malware |
|
DHCP |
Disabled service, router
misconfiguration, static IP conflicts |
|
Firewall |
Overly restrictive rules,
third-party security software conflicts |
🌐 3. Fixing DNS Issues
Step 1: Flush DNS Cache
Open
Command Prompt (Admin) and run:
ipconfig
/flushdns
Step 2: Reset Network Stack
netsh
winsock reset
netsh
int ip reset
Restart
your computer afterward.
Step 3: Change DNS Server
1.
Open Control Panel → Network and
Internet → Network Connections.
2.
Right-click your network → Properties
→ Internet Protocol Version 4 (TCP/IPv4).
3.
Select Use the following DNS
server addresses and enter:
o Preferred: 8.8.8.8
o
Alternate: 8.8.4.4
(Google DNS — or use Cloudflare: 1.1.1.1)
Step 4: Restart DNS Client Service
services.msc
→ DNS Client → Restart
Step 5: Check Router DNS Settings
- Log in to router settings (192.168.0.1
or 192.168.1.1).
- Under Internet or WAN settings, set manual DNS
(Google or Cloudflare).
🖧 4. Fixing DHCP Issues
Step 1: Renew IP Address
Open
Command Prompt and run:
ipconfig
/release
ipconfig
/renew
Step 2: Restart DHCP Client Service
1.
Press Win + R, type services.msc.
2.
Locate DHCP Client,
right-click → Restart.
3.
Set Startup Type: Automatic.
Step 3: Check Router DHCP Configuration
- Ensure DHCP server is enabled.
- Verify the IP range (e.g., 192.168.1.2
to 192.168.1.100).
- Avoid overlapping IP ranges if using multiple routers.
Step 4: Assign a Manual IP
If
DHCP fails, manually assign:
IP:
192.168.1.200
Subnet:
255.255.255.0
Gateway:
192.168.1.1
DNS:
8.8.8.8
Step 5: Check for MAC Filtering
Some
routers block unknown devices. Disable MAC filtering or add your
device’s MAC address to the allowed list.
🔥 5. Fixing Firewall Issues
Step 1: Temporarily Disable Firewall
To
test connectivity:
1.
Go to Control Panel → Windows
Defender Firewall → Turn Windows Defender Firewall on or off.
2.
Disable both public and private
firewalls temporarily.
(If internet works now, your firewall rules need adjustment.)
Step 2: Allow an App Through Firewall
1.
Go to Firewall → Allow an app or
feature through Windows Defender Firewall.
2.
Add your program (e.g., Chrome,
Steam, File Sharing).
Step 3: Reset Firewall Settings
netsh
advfirewall reset
Step 4: Check Third-Party Firewalls
Security
software like Norton, McAfee, or BitDefender may block connections.
- Temporarily disable or
reconfigure them.
- Add trusted applications to the
allowlist.
⚡ 6. Advanced Troubleshooting
Check DNS with Ping
ping
google.com
ping
8.8.8.8
- If the first fails but second works → DNS problem.
- If both fail → network or DHCP issue.
Check IP Configuration
ipconfig
/all
- If IP starts with 169.254.x.x, DHCP failed.
- If DNS shows 0.0.0.0, fix via manual configuration.
View Firewall Logs
Open
Event Viewer → Applications and Services Logs → Microsoft → Windows →
Windows Firewall with Advanced Security → Firewall.
Look for “Blocked Connections” events.
🧱 7. Preventing Future Issues
1.
Keep
router firmware updated.
2.
Use reliable DNS providers
like Google (8.8.8.8) or Cloudflare (1.1.1.1).
3.
Avoid setting static IPs within the
DHCP range.
4.
Regularly scan for malware,
which can hijack DNS settings.
5.
Backup and export your firewall
configuration after customization.
6.
Enable DHCP reservations for
key devices to avoid IP conflicts.
🧰 8. macOS and Linux Solutions
macOS
- Flush DNS:
·
sudo dscacheutil -flushcache; sudo
killall -HUP mDNSResponder
- Renew DHCP Lease:
System Settings → Network → Advanced → TCP/IP → Renew DHCP Lease
Linux
- Restart networking:
·
sudo systemctl restart
NetworkManager
- Renew IP:
·
sudo dhclient -r && sudo
dhclient
- Flush DNS:
·
sudo systemd-resolve --flush-caches
✅ 9. When to Contact Support
- DNS or DHCP errors persist
across multiple devices.
- Router fails to assign IPs even
after a factory reset.
- You suspect malware or
corrupted system files.
- ISP DNS outage or network-wide
configuration issue.
🏁 Conclusion
DNS,
DHCP, and firewall issues are common yet highly fixable with the right
approach. By understanding how these components interact, you can quickly
identify whether the issue lies in your system, router, or network. Regular maintenance
— like clearing caches, updating firmware, and managing firewall rules —
ensures smooth, secure, and reliable connectivity.
Written by: UltraTechGuide
For more networking and system troubleshooting guides, visit: ultratechguide.blogspot.com
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