How to Diagnose Internet Problems with Command Prompt

Command Prompt cannot increase the speed supplied by your internet provider, but it can help identify a local connection problem and repair specific DHCP or DNS issues. Test speed before and after any change, and avoid copying broad netsh “optimization” scripts.

Open an elevated Command Prompt

Open Start, type Command Prompt, and select Run as administrator when a repair command requires it.

Inspect the network configuration

Run:

ipconfig /all

Find the active Ethernet or Wi-Fi adapter. Check that it has an IPv4 address, Default Gateway, DHCP server, and DNS servers. An address beginning with 169.254 often indicates that Windows did not receive an address from DHCP.

Test the local router

Ping the Default Gateway shown for the active adapter:

ping -n 20 GATEWAY_ADDRESS

Low, consistent response times indicate that the local path to the router is working. Packet loss or large variations suggest a Wi-Fi, cable, adapter, or router issue. A router can also be configured not to answer ping, so a timeout is not conclusive by itself.

Renew a DHCP address when it is invalid

If Windows has an invalid DHCP address or the network changed, run:

ipconfig /release
ipconfig /renew

This disconnects the adapter briefly and requests a new address. It does not create more bandwidth. Do not use it on a computer with a manually assigned static IP unless you understand that configuration.

Clear the DNS resolver cache

If one or more domain names resolve incorrectly while the connection otherwise works, run:

ipconfig /flushdns

This clears cached DNS records. It does not speed up a healthy connection, and the next lookup may take slightly longer while Windows retrieves a fresh answer.

Do not disable TCP auto-tuning as a generic tweak

The commands shown in some older guides disable TCP receive-window auto-tuning and heuristics.

These are not universal speed improvements and can reduce throughput or complicate troubleshooting. If auto-tuning was previously disabled, an administrator can inspect the current settings with netsh interface tcp show global and restore the normal level with netsh interface tcp set global autotuninglevel=normal.

Find the actual bottleneck

• Compare Ethernet and Wi-Fi on the same PC.
• Test another device on the same network.
• Pause VPNs, cloud backups, downloads, and game updates for a controlled test.
• Restart the router and PC when appropriate.
• Update the network-adapter driver from the PC or adapter manufacturer.
• Contact the provider if every device is slow outside the local network.

For more diagnostic commands, see the basic network troubleshooting tools. If Windows shows a warning icon, use the targeted guide for a network connection with a yellow exclamation mark.