How To • VPN • Troubleshooting

How to troubleshoot DNS with work VPN access

This guide will help you identify and fix DNS issues that appear when your work VPN is active, such as websites not loading while you remain connected. You'll learn to diagnose whether the problem is with the VPN, your device, or your local network, and apply targeted fixes to restore normal browsing.

By the end, you'll be able to systematically isolate the cause and implement solutions like adjusting DNS settings or network configurations.

Note: Steps may vary by device and router model. This guide focuses on safe, general methods.

Quick Answer

Disconnect your VPN and test your internet to confirm the issue is VPN-related.
On your computer, open Command Prompt (Windows) or Terminal (macOS/Linux) and run ping 8.8.8.8. If this works, you have a DNS issue.
Try changing your device's DNS server to a public one like Google (8.8.8.8) or Cloudflare (1.1.1.1).
Check if your VPN client has a "split tunneling" setting and ensure it's configured correctly for your needs.
Flush your device's DNS cache and restart the VPN client.
As a temporary test, connect to a different network (e.g., a mobile hotspot).

If this doesn't work, follow the detailed diagnostic flow and step-by-step guide below.

What you need

Before you start

Your work-issued VPN client and login credentials.
Administrator or sudo access on your computer to change network settings.
A basic understanding of how to open a terminal/command line.
Access to your local router's admin page (optional, but helpful).
A secondary internet connection (like a phone hotspot) for testing.

Good to know

DNS translates website names (like google.com) to IP addresses.
VPNs often override your default DNS settings with their own servers.
Some corporate networks block external DNS for security.
"Split tunneling" lets some traffic bypass the VPN.
Your IT department may have specific DNS policies.
Firewall settings can interfere with DNS queries.

Diagnose the issue in 2 minutes

Step 1: Is it only one device or all devices?
- One device: Problem is likely on that device or its VPN client.
- All devices: Problem may be with your router or ISP.
Step 2: Does it happen only when the VPN is on?
- VPN off = internet works: The VPN is causing the issue.
- VPN off = internet broken: Your local network or ISP has a problem.
Step 3: Can you ping an IP address but not a website?

ping 8.8.8.8

If this succeeds (you get replies)...

ping google.com

If this fails (unknown host), you have a classic DNS failure.
Step 4: Is it all websites or just some?
- All websites: General DNS or connection failure.
- Specific sites (especially work/internal): Could be VPN routing or firewall rules.

Step-by-step guide

Step 1 — Establish a baseline without VPN

Disconnect your VPN completely and test your basic internet connectivity.

Fully quit the VPN client software.
Open a web browser and visit a common site like google.com.
If the internet works, the VPN is the source of the problem.

What you should see: Normal, fast loading of websites without the VPN connected.

Step 2 — Test connectivity with ping commands

Use the command line to test basic network reachability and DNS.

Open your command line tool (Terminal, Command Prompt, PowerShell).
Type ping 8.8.8.8 and press Enter. Look for reply lines.
Then type ping google.com and press Enter.

What you should see: Successful pings to both. If the IP works but the domain name fails, DNS is broken.

Windows: Use Command Prompt or Windows PowerShell. Type cmd in the Start menu search.

macOS: Open Terminal from Applications > Utilities.

Linux: Use your distribution's terminal application (Ctrl+Alt+T often works).

Step 3 — Check your active DNS servers

Find out which DNS servers your device is currently using, both with VPN on and off.

With VPN off, run ipconfig /all (Windows) or scutil --dns (macOS) or nmcli dev show | grep DNS (Linux). Note the DNS servers.
Connect the VPN and run the same command again. The DNS servers will often change.

What you should see: Different DNS server addresses when the VPN is active. If they appear as private IPs (like 10.x.x.x), they are from your VPN.

Step 4 — Flush the local DNS resolver cache

Clear out old, possibly corrupted DNS entries stored on your computer.

In your command line, run the flush command for your operating system.

What you should see: A confirmation message like "Successfully flushed the DNS Resolver Cache."

Windows: Run ipconfig /flushdns in an Administrator Command Prompt.

macOS: Run sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder.

Linux: The command varies. For systemd-resolved, run sudo systemd-resolve --flush-caches.

Step 5 — Manually set a public DNS server

Temporarily override DNS settings on your device to see if the VPN's DNS server is the problem.

Go to your computer's network settings.
Find the DNS server setting for your active connection (Wi-Fi or Ethernet).
Change it from "Automatic" to "Manual".
Add addresses like 8.8.8.8 (Google) and 1.1.1.1 (Cloudflare).
Reconnect your VPN and test.

What you should see: If websites now load, the VPN's default DNS servers were the issue. Note: Some corporate VPNs may override this setting.

Step 6 — Inspect VPN client settings

Look for VPN-specific features that control DNS and network routing.

Open your VPN client's settings or preferences.
Look for options like "Split Tunneling", "DNS Leak Protection", or "Custom DNS".
If split tunneling is available, try enabling it and excluding your web browser or general internet traffic from the VPN tunnel.
If DNS leak protection is on, try disabling it temporarily as a test.

What you should see: A change in behavior when these settings are adjusted. Be aware that changing these may have security or policy implications for work.

Step 7 — Test on a different network

Rule out problems with your local internet provider or router.

Disconnect from your home Wi-Fi.
Connect your computer to a different network, such as your phone's mobile hotspot.
Reconnect the VPN and test browsing again.

What you should see: If the problem disappears, the issue may be with your primary ISP's interaction with the VPN or your router's firewall.

Step 8 — Update and restart

Ensure your software is current and perform a clean restart cycle.

Update your VPN client to the latest version.
Update your computer's network drivers (especially important on Windows).
Fully restart your computer and your router.
Attempt the VPN connection again from a fresh state.

What you should see: A clean connection with updated software. This resolves many transient glitches.

Common fixes by symptom

Websites timeout with VPN on

Likely causes:

VPN DNS servers are slow or unreachable.
Corporate firewall is blocking external DNS queries.
MTU size mismatch causing packet fragmentation.

Safe fixes:

Manually set your device DNS to a public server.
In VPN settings, disable "DNS Leak Protection".
Lower the MTU setting on your device's network adapter.

Stop if: You cannot connect to any internal work resources after changes.

Only some websites don't load

Likely causes:

VPN's DNS is blocking specific domains for security.
Split tunneling is misconfigured.
Hosts file on your computer is interfering.

Safe fixes:

Check with your IT department if the site is intentionally blocked.
Review split tunneling rules to ensure the site's traffic is routed correctly.
Temporarily rename your hosts file (located at /etc/hosts or C:\Windows\System32\drivers\etc\hosts).

Stop if: The site is a critical work-related internal site that fails.

Internet works, but is very slow

Likely causes:

All traffic is being routed through a distant VPN server.
DNS resolution is adding significant delay.
Network congestion on the VPN tunnel.

Safe fixes:

Use split tunneling to exclude non-work traffic from the VPN.
Switch to a faster public DNS provider.
Connect to a geographically closer VPN server if your company allows.

Stop if: Speed is still unacceptable after trying split tunneling.

Can't access local network devices

Likely causes:

VPN is in "full tunnel" mode, isolating you from your local LAN.
Firewall rules on your router are blocking local traffic.

Safe fixes:

Enable "Allow local network access" in your VPN client settings (if available).
Check your router for client isolation or AP isolation settings and disable them.

Stop if: Your corporate security policy explicitly forbids local network access while on VPN.

VPN connects but no internet at all

Likely causes:

VPN is overriding your default gateway incorrectly.
IP address conflict on the VPN network.
Critical system network service is stopped.

Safe fixes:

Run the network troubleshooter on your OS.
Check for IP address conflicts by releasing/renewing your DHCP lease.
Restart network services (e.g., "WLAN AutoConfig" service on Windows).

Stop if: You suspect a corporate policy is intentionally limiting internet access.

Intermittent DNS failures

Likely causes:

Unstable connection to the VPN DNS server.
DNS cache corruption recurring.
Antivirus or security software interfering.

Safe fixes:

Set a static DNS server as in Step 5 of the guide.
Schedule a regular task to flush DNS cache.
Temporarily disable third-party firewall/antivirus to test.

Stop if: The interference is coming from mandated corporate security software you cannot modify.

Quick reference

Table A: What the metric means

Metric	What it is	Good baseline
Latency (Ping)	Round-trip time for a data packet. High latency feels like lag.	< 50ms to your VPN server.
Jitter	Variation in latency. Causes voice/video choppiness.	< 20ms.
Packet Loss	Percentage of data packets that fail to arrive.	0%. Anything above 1% is problematic.
Throughput	Actual download/upload speed you experience.	Within 80% of your plan's speed with VPN off.
Signal Strength (Wi-Fi)	Quality of your wireless connection to the router.	-60 dBm or better (closer to 0).

Table B: Safe baseline settings

Setting	Recommendation	VPN Consideration
Wi-Fi Security	Use WPA2/WPA3 Personal. Avoid WEP or open networks.	A secure local network adds a layer before VPN encryption.
DNS Server	Use reputable public DNS (e.g., 8.8.8.8, 1.1.1.1) for testing.	VPN may override this. Manual setting can bypass faulty VPN DNS.
Router Admin	Change default login, keep firmware updated.	Prevents local network compromises that could affect VPN traffic.
Guest Network	Enable for visitors and IoT devices.	Isolates untrusted devices, reducing local network issues during VPN use.
Updates	Auto-update OS, network drivers, and VPN client.	Fixes known bugs that cause VPN dropouts and DNS problems.

Mind map summary

DNS Problem with Work VPN
|
+-- Is it really DNS?
|   |
|   +-- Test: ping 8.8.8.8 (works) vs ping google.com (fails) = DNS issue.
|   +-- Test: VPN off = internet works? If yes, VPN is the cause.
|
+-- Where is the failure?
|   |
|   +-- On the Device
|   |   +-- Flush DNS cache (ipconfig /flushdns, etc.)
|   |   +-- Change DNS server manually to 8.8.8.8
|   |   +-- Update VPN client & network drivers
|   |
|   +-- In the VPN Configuration
|   |   +-- Check "Split Tunneling" settings
|   |   +-- Disable "DNS Leak Protection" temporarily
|   |   +-- Try a different VPN server/gateway
|   |
|   +-- In the Local Network
|       +-- Restart router
|       +-- Test on a different network (hotspot)
|       +-- Disable router firewall briefly to test
|
+-- Quick Remedies (try in order)
|   |
|   +-- 1. Flush DNS & Renew IP (ipconfig /release & /renew)
|   +-- 2. Set static public DNS on device
|   +-- 3. Enable split tunneling for web traffic
|   +-- 4. Switch from Wi-Fi to Ethernet
|   +-- 5. Reinstall/update VPN client
|
+-- When to Stop
    |
    +-- Internal work resources break
    +-- IT policy prohibits the change
    +-- Suspected security conflict
    -> Escalate to IT support with collected data.

Troubleshooting checklist

Device

Flush DNS cache
Set manual DNS to 8.8.8.8 / 1.1.1.1
Disable third-party firewall/antivirus (test)
Update network adapter drivers
Switch between Wi-Fi and Ethernet
Restart the device

Router

Power cycle (unplug for 30 seconds)
Check for firmware updates
Disable any "QoS" or "Traffic Prioritization"
Temporarily disable firewall/security features
Ensure NAT is enabled

ISP & VPN

Test connection on a different network
Check VPN server status with IT
Try a different VPN protocol (if allowed)
Contact ISP to check for throttling/blocking
Collect speed test results (VPN on/off)

When to escalate

Contacting your IT support

Do this if you've tried all safe device-side fixes and the problem prevents you from working. This is especially true if internal company websites or applications fail to load.

Contacting your ISP

Escalate if the problem only occurs on your home network (works fine on other networks) and your router restart didn't help. Persistent packet loss or high latency to the VPN gateway are also ISP-level issues.

Considering router replacement

If your router is many years old, cannot handle multiple VPN connections, or consistently fails with VPN traffic while other networks work, it may be a hardware limitation.

What to collect before escalating

Results of ping 8.8.8.8 and ping your-vpn-gateway
Output of tracert 8.8.8.8 (Windows) or traceroute 8.8.8.8 (macOS/Linux)
Speed test results with VPN on and off
Exact error messages from the VPN client
The time of day the problem occurs and how often
Whether other devices on the same network have the same issue

FAQ

Why does my VPN change my DNS server?

For security and policy enforcement. By controlling DNS, your company can ensure that internal website names resolve correctly and can filter or log internet access. It also prevents DNS leaks, where your browsing queries could be seen by your local ISP.

Is it safe to change my DNS to a public server while on VPN?

It is generally safe from a technical standpoint, but it may violate your company's IT policy. Using an external DNS server means your employer cannot apply their DNS-based security filters or internal domain resolution. Always check with IT if you're unsure.

What is split tunneling and should I use it?

Split tunneling lets you route only specific traffic (like work apps) through the VPN, while other traffic (like general web browsing) goes directly through your local internet. It can speed up browsing and reduce DNS conflicts. Use it if your company allows it, as it eases the load on both your device and the VPN server.

Can my ISP block or interfere with my VPN connection?

Yes, though it's uncommon. Some ISPs may throttle or inadvertently interfere with VPN traffic, especially on certain ports. Symptoms include consistent timeouts only when the VPN is active. Testing with a mobile hotspot can confirm this.

Why do I lose access to my local printer and smart home devices when I connect to VPN?

Most VPNs are configured for "full tunnel" mode, which routes all your traffic to the corporate network. This often disallows connections to devices on your local home network for security reasons. Check your VPN client for a "Allow local (LAN) access" setting.

How often should I flush my DNS cache?

Only when you're experiencing DNS-related problems like being unable to access a website that you know is online. There's no need for regular maintenance flushing.

Will using a VPN affect my internet speed?

Yes, usually. Your data takes a longer route through the VPN server, and encryption adds overhead. A 10-20% speed reduction is normal. If the slowdown is extreme (>50%), it could be due to a slow VPN server, DNS issues, or a congested network path.

What should I do if only one application (like a web browser) has DNS issues?

Try these steps in order: Clear that specific browser's cache and cookies. Check if the browser is using a secure DNS (DoH) setting that might conflict with the VPN. Try a different browser. Reinstall the problematic application.

Sources and references

Microsoft Windows networking command-line reference (ipconfig, ping, nslookup)
Apple macOS support documentation for network diagnostics and DNS configuration
Linux man pages for systemd-resolved, NetworkManager, and ip commands
General VPN operation and split tunneling concepts from major VPN vendor guides
DNS protocol basics from IETF RFC documents (RFC 1034, RFC 1035)
Home router administration and firmware update best practices
IEEE 802.11 Wi-Fi standards for understanding local network connectivity
Cybersecurity best practices for remote work and VPN usage
Common network troubleshooting methodologies (OSI model layered approach)

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How to troubleshoot DNS with work VPN access

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