What is an acceptable level of packet loss?

0% is ideal; under 0.5% is generally unnoticeable. Above 1% you'll feel it in video calls and gaming. Above 5% is severely disruptive for any interactive workload.

What's the most common cause of packet loss?

Wi-Fi interference, by a wide margin. Drop the Wi-Fi, test wired, and most home packet-loss complaints disappear or relocate to the upstream provider.

Can a bad cable cause packet loss?

Yes — damaged Ethernet cables, loose connectors, and pinched cables under furniture are common culprits. Swap suspect cables before chasing ISP gremlins.

Does packet loss mean my ISP is bad?

Not always. Run a traceroute during a loss event — if loss starts at your router or first hop, it's local. If loss starts at an upstream hop, contact the ISP with the trace data.

What Causes Packet Loss — A Diagnostic Field Guide

Packet loss is the single most disruptive network defect because it converts smooth interactive workloads into stuttering ones. The causes form a short list — and a systematic triage workflow finds the culprit faster than guessing.

Local Wi-Fi (most common)

Wi-Fi shares airtime with neighbors and household devices. Interference, weak signal, and channel congestion all manifest as packet loss. Symptoms: loss disappears when you plug in via Ethernet.

Fix: move closer to the AP, change channels, consolidate onto less-congested 5/6 GHz bands, add a mesh node or wired AP for the affected area.

Saturated upload

Cable plans often have modest upload bandwidth (10–35 Mbps). One device uploading a large backup can saturate the upstream and cause loss in both directions because TCP ACKs can't get back. Symptoms: loss spikes coincide with cloud sync, backups, or video uploads.

Fix: throttle the upload, schedule it for off-hours, or enable router-level QoS / SQM to prevent any single flow from monopolizing the upstream.

Bufferbloat

Excessive buffering in your modem or router during congestion creates massive latency spikes and indirect loss. Run the bufferbloat-aware speed test — loaded latency well above idle latency is the signature.

Fix: a router with fq_codel or CAKE qdiscs enabled (most modern routers support SQM).

Faulty cabling and connectors

Crushed Ethernet, corroded coax connectors, kinked patch cables. Symptoms: persistent low-level loss that doesn't change with usage; sometimes accompanied by speed-test variability.

Fix: swap suspect cables one at a time; reseat coax connectors; replace any cable older than ~10 years that's seen rough handling.

ISP / upstream issues

Maintenance, fiber cuts, peering disputes, neighborhood congestion at peak hours. Symptoms: loss appears past your router in traceroutes, often time-of-day correlated.

Fix: collect traceroutes with timestamps and open a ticket with concrete data — 'internet is slow' tickets get triaged slowly; 'consistent 5% loss at hop 4 between 7–10pm' tickets escalate fast.

The triage workflow

Reproduce loss while plugged in via Ethernet. If it disappears, the problem is Wi-Fi.
Run continuous ping to your gateway. Loss there = local network.
Run continuous ping to 1.1.1.1. Loss past the gateway = ISP/upstream.
Traceroute during a loss event. Pin down the hop where loss begins.
Reproduce at different times of day to distinguish congestion from hardware faults.

What causes packet loss — and how to isolate it