WAN port freezing? How to find packet loss with traceroute

What happens when your internet freezes at the WAN port

When the WAN port, which is the entry and exit interface of your router connected to the ISP, starts failing, it feels like the entire internet has stopped. Pages take forever to load, video calls drop, and online games suffer from frustrating lags. In practice, this means data packets, which are small chunks of information sent by your computer, are getting lost along the way to their final destination on the internet. To find out exactly where the issue lies, we need to look beyond the home router and examine the path data takes across provider networks.

Often, we blame Wi-Fi or the home device itself, but the real flaw lies in intermediate hops within the carrier infrastructure or international transit servers. The major challenge for network admins and curious users is isolating the exact failure point without relying solely on superficial speed tests. This is precisely where traceroute comes in, a classic utility present in almost every modern operating system. It allows you to map every router your packet passes through, revealing response times and potential bottlenecks.

How traceroute works behind the scenes

To understand traceroute, we must grasp the concept of TTL, which stands for Time to Live. Every data packet sent across the network carries a header number that decreases by one unit each time it passes through a router. When this number hits zero, the current router discards the packet and sends back an error message stating that the time has expired. Traceroute exploits this exact behavior in an ingenious way.

The program sends the first packet with a TTL of one, causing it to die on the very first hop, which is usually your own router. The router replies, and the program discovers the IP address of this first hop. Next, it sends another packet with a TTL of two, which dies on the second router, revealing its identity. This process repeats incrementally until the packet finally reaches its destination. If you want to take your analysis further with a tool that combines this tracking with real-time measurements, check out our guide on how to diagnose packet loss with mtr tool to monitor ongoing instabilities.

Running the command and interpreting results

In daily operations, running the command in the terminal is simple, but interpreting the text-filled screen requires attention to detail. You can open the command prompt on Windows or the terminal on Linux and macOS and type the command followed by a destination address, such as a website or a reliable public IP. Each line displayed on the screen represents a physical or logical hop the packet crossed within the telecommunications infrastructure.

The columns typically show the hop number, three response times in milliseconds, and the corresponding IP address or router name. If you notice that response time jumps from five milliseconds to one hundred fifty milliseconds suddenly, you have found a relevant delay point. If you need to investigate whether malicious traffic or unwanted packets are interfering with this route, you can also complement your analysis by studying how to block malicious network packets with iptables to shield your environment from external interference.

traceroute 8.8.8.8

When analyzing the output of the command above, each line will reveal an intermediate router up to Google's DNS server. It is essential to note that the standard Linux traceroute uses UDP packets, while Windows typically uses ICMP requests. This technical difference matters because some corporate or carrier firewalls block UDP protocol on high ports, causing certain hops to appear as asterisks on the screen, even if traffic is flowing normally through them.

Distinguishing real packet loss from false positives

One of the biggest mistakes when analyzing a traceroute is panicking upon seeing asterisks or packet loss rates on intermediate hops. In practice, core routers of large internet service providers prioritize the rapid forwarding of millions of packets and leave diagnostic test responses as a low processing priority. Therefore, if an intermediate hop shows one hundred percent loss, but the next hop responds perfectly with low times, you can safely ignore that alert.

True critical packet loss occurs when an intermediate hop starts dropping packets and all subsequent hops inherit that same failure or exhibit uncontrolled rising latency up to the destination. If the problem persists on your WAN port and you notice constant oscillations, it is worth checking the physical integrity of edge equipment and cables, much like we do when testing quartz crystal oscillators and clock circuits on the workbench to ensure hardware glitches are not causing intermittent instabilities.

Final considerations on route troubleshooting

Mastering traceroute transforms how you view connectivity issues, taking the guesswork out of tech support. Instead of rebooting the modem blindly, you begin to identify whether the bottleneck is in your local network, the router WAN port, ISP servers, or the ultimate destination. By combining this reading with complementary monitoring tools and sound network engineering practices, you gain the autonomy to demand assertive solutions from your internet provider and keep your services running smoothly.