Slow internet: the 3 tests that distinguish router delay from ISP issues

Part of our guide on tech ops vs dev ops difference

Three practical tests that anyone can do to tell if slow internet is your router’s fault or your ISP’s.

What you need to test if slow internet is router or ISP

Prepare three tools to diagnose slow internet: your router with its power adapter, a computer or smartphone that can connect by Wi-Fi and Ethernet, and your internet modem.

You will also need access to your router’s admin interface, which typically requires a web browser and the router’s IP address or app.

Familiarity with basic network commands like ping and traceroute may help, but free apps on Windows, Mac, Android, and iPhone provide easy access.

Consider the type of internet connection you have, as this affects testing methods. Fiber and cable connections usually allow for reliable direct modem testing, but DSL users may find that connecting directly to the modem does not bypass all router functions because of built-in router features on some DSL modems. Knowing your connection type helps interpret results correctly. We go through quick fixes for update issues step by step elsewhere on the site.

Also prepare to note the typical speed range provided by your ISP plan. For example, a 100 Mbps plan normally delivers between 80 to 120 Mbps under good conditions. Comparing your test results against this expected range will clarify if speeds are unusually slow or within normal fluctuations.

• Router and power adapter
• Modem with Ethernet port
• Computer or smartphone for testing
• Web browser or router admin app
• Ping and traceroute tools or apps

Step 1: reboot your router and check speed improvements

Restarting the router clears memory and network congestion. This simple step fixes roughly 40-60% of temporary slowdowns.

Unplug the router’s power, wait at least 30 seconds, then plug it back in. Wait for all indicator lights to stabilize. Before you commit to anything, it is worth looking at internet speed test pc.

After reboot, run an internet speed test on speedtest.net or a similar site to measure download and upload rates.

If rebooting yields no speed improvement, try waiting a few minutes longer before retesting, as some routers take time to optimize connections post-reboot. For instance, speeds may only increase noticeably after 5 minutes once device caches refresh.

If reboot does improve speeds temporarily but slowdowns return quickly, the router may be overheating or running outdated firmware. In this case, check for firmware updates or improve router ventilation. An overheated router can cause packet loss, visible as intermittent speed drops during tests. It helps to understand how tech things work before going further.

1. Unplug router power cable.
2. Wait 30-60 seconds to clear cache.
3. Plug power back in and wait for stable lights.
4. Run internet speed test on a connected device.
5. Compare speed to your usual speeds and ISP plan.

Step 2: test internet speed bypassing the router by connecting directly to the modem

Connecting your computer directly to the modem removes the router from the equation, so any slow speeds here reveal ISP or modem issues.

Use an Ethernet cable to connect your device to the modem’s LAN port. Disable Wi-Fi on the device to avoid confusion.

Run the same speed test again. If speeds improve significantly, your router may be the bottleneck. If that sounds like your situation, read up on understanding technical terms next.

If direct modem testing still shows slow speeds, verify whether the modem’s firmware is current. Outdated modem firmware can limit performance. Contact your ISP or check the modem manufacturer’s site for updates.

Note that some ISPs use modems combined with router functions, called gateway devices. In such cases, direct connection tests may not isolate the router, and contacting ISP support for further diagnostics is recommended.

A worked example: if your ISP plan is 200 Mbps, and your direct modem test shows only 50 Mbps, this suggests an ISP or modem issue. Conversely, if the direct test is 180 Mbps but router-connected speed is 60 Mbps, the router likely causes the bottleneck. There is more on tech debt lifecycle and recovery sequence in a separate guide.

1. Power off router and modem.
2. Disconnect router from modem.
3. Connect device directly to modem via Ethernet.
4. Power on modem and wait for online status.
5. Disable Wi-Fi on device to use wired test only.
6. Run internet speed test and note results.

Step 3: use ping and traceroute to identify where delays occur

Ping measures round-trip time to a server, letting you see if delays start inside your network or beyond your ISP.

Traceroute shows the path packets take, listing each 'hop' from your device to the destination server and the time for each hop.

Run ping tests to your ISP gateway first, then to a public server like 8.8.8.8 (Google DNS). High ping (>100ms) early in the path shows router or local network issues. We go through performance and complexity tradeoffs step by step elsewhere on the site.

When running ping tests, average the results of at least 10 packets to reduce variability. For example, an average ping under 30ms to your ISP gateway is normal for most broadband connections; higher averages suggest local network delays.

Traceroute outputs can be complex; look for large jumps in latency between consecutive hops. A sudden increase from 20ms to 150ms between hops indicates the problem likely starts at that hop. Consistent packet loss (indicated by asterisks) also signals network issues at specific routers.

If ping tests to the ISP gateway show low latency, but pings to external servers are high or unstable, the ISP's external network may be congested or faulty. This distinction helps you decide whether to escalate the issue to the ISP or focus on home network fixes.

1. Open command prompt or terminal.
2. Type 'ping [ISP gateway IP]' and note response times.
3. Type 'ping 8.8.8.8' and compare response times.
4. Run 'traceroute [8.8.8.8]' (or 'tracert' on Windows).
5. Identify hops with high latency or packet loss.
6. If delays occur after ISP gateway, issue is likely ISP.

How to check router settings and hardware for slow internet causes

Old or misconfigured routers often throttle speeds. Check your router’s firmware version and update if possible.

Examine settings for bandwidth limits, Quality of Service (QoS), and device prioritization that might slow some connections.

Also check if many devices are connected simultaneously, as this can saturate router capacity and cause slowdowns.

• Firmware update: improves performance and security
• QoS settings: prioritize critical traffic or disable if causing issues
• Bandwidth limits: ensure none are set too low
• Connected devices: disconnect unused devices to test impact

How to interpret test results to pinpoint if slow internet is router or ISP

If reboot fixed speed, the router had a temporary glitch. If direct modem test is slow, the ISP or modem is likely at fault.

Ping and traceroute showing high delay within your home network or router means local issues; delays starting beyond the ISP gateway indicate ISP problems.

If all tests show normal speeds but you still experience slowdowns, consider Wi-Fi interference or device issues.

Common mistakes when diagnosing slow internet and what to do instead

Many users diagnose slow internet solely based on Wi-Fi speeds, ignoring that Wi-Fi interference or signal strength issues can mask the real cause. Always test with a wired Ethernet connection first to separate wireless issues from core network problems.

Another common mistake is to rely on a single speed test result. Internet speeds can fluctuate due to time of day, network congestion, or server load. Repeat tests at different times, averaging results to get an accurate picture.

Failing to consider the number and activity of connected devices during tests can lead to misdiagnosis. Heavy streaming or downloads on other devices during testing will reduce available bandwidth, falsely suggesting router or ISP problems. Disconnect or pause all other devices to perform accurate tests.

• Ignoring router reboot: restart router before any other test.
• Skipping direct modem test: always isolate router by direct connection.
• Only testing Wi-Fi: test wired connection to remove interference factors.
• Misreading ping results: consider typical latency thresholds before blaming ISP.
• Not updating router firmware: keep router software current for best speed.

Questions people still ask

I've personally used these exact tests to isolate slow internet causes, saving time and avoiding unnecessary ISP calls.