“The network is slow” can mean dozens of things: the internet is slow, the financial software takes a long time to open, copying files from the server drags on, or just one room has weak Wi-Fi. If you start troubleshooting by replacing the router or buying more bandwidth, you may spend money and still have the problem. The right approach is to narrow down the scope of the problem step by step.
Step 1: Define the Problem Precisely
Before running any tests, answer these questions:
- Who? One person, one department, one floor or everyone?
- What? Is everything slow, only the internet, or only a specific application?
- When? Always, at certain times of day, or since a specific change?
- Wired or Wi-Fi? Is it the same with a wired connection?
These four answers usually get you halfway there. A problem affecting one person often comes down to their computer, cable or port; a problem affecting all users points to the network core, the internet or a server.
Step 2: Check the Physical Layer
Many local slowdowns have a physical root cause:
- Link speed: in the network adapter status, check whether the connection is at 1 Gbps or 100 Mbps. A faulty cable or jack often silently lowers the speed.
- Port errors: on a managed switch, check each port’s error counters, such as CRC errors. Rising error counts mean a problem with the cable, jack or port.
- Swap test: try a known-good patch cord or a different port.
Step 3: Internal Network or Internet?
From the user’s computer, use the ping command to test, in order, the network gateway, an internal server and an internet address. On Windows, send a hundred packets with a command such as ping -n 100 10.0.0.1 and pay attention to two things: response time and the number of lost packets. On a healthy local network, response times are very low with no packet loss.
- If pings to the gateway are already high or show packet loss, the problem is inside the local network.
- If the internal network is healthy and only the internet path has problems, use
tracertto view the route and check the internet link’s usage.
To measure actual throughput between two internal points, the iperf3 tool is very useful: run iperf3 -s on one side and iperf3 -c with the first side’s address on the other.
Step 4: Who Is Using the Bandwidth?
If the internet slows down at certain times, the link is probably saturated. Check the firewall’s traffic report: a cloud backup, cloud storage sync, dozens of computers updating at once, or one user’s large download can take up the entire link. The solution is usually to schedule heavy tasks outside working hours and to prioritize traffic (QoS), not necessarily to buy more bandwidth.
Step 5: DNS, Servers and Wi-Fi
- Slow DNS: if every new site pauses before opening but then loads at normal speed, check DNS response time with
nslookup. - Server: when only one application is slow and the network looks healthy, check the server’s processor, memory and disk usage. Many “network slowdowns” are actually slow server disks or databases.
- Wi-Fi: channel interference, too much distance from the access point, or too many users on one device.
If the entire network suddenly becomes extremely slow or goes down and the switch lights are blinking constantly and in sync, suspect a network loop and disconnect the last cable or device that was plugged in.
Checklist
- The scope of the problem is defined: who, what and when.
- Link speed and port errors have been checked.
- Ping has shown whether the problem is internal or on the internet side.
- Internet link usage during the slowdown has been reviewed.
- DNS and server resources have been checked.
- The cause and solution have been recorded for next time.
If your company network keeps slowing down and the root cause has not been found, ITPlus724 engineers can troubleshoot the network and recommend a lasting solution.