internet-troubleshooting - SKILL.md Agent Skill

name: internet-troubleshooting description: Diagnose and fix slow internet issues on Linux (Fedora)

Internet Troubleshooting Skill

Quick Diagnostics Checklist

Run these in parallel to diagnose:

# 1. Check connection type and devices
nmcli device status

# 2. Check for VPN/tunnels that may throttle
ip link show | grep -E 'wg|tun|tap'

# 3. Speed test
curl -o /dev/null -w "Speed: %{speed_download} bytes/sec\nTime: %{time_total}s\n" https://speed.cloudflare.com/__down?bytes=10000000

# 4. Ping test (latency + packet loss)
ping -c 5 8.8.8.8

# 5. DNS check
cat /etc/resolv.conf

# 6. Test DNS response time
dig google.com @<dns-server> +time=2 +stats

# 7. Ethernet link details
ethtool <interface> | grep -iE 'speed|duplex|link'

# 8. Network errors
cat /sys/class/net/<interface>/statistics/rx_errors
cat /sys/class/net/<interface>/statistics/tx_errors

Common Fixes

Dead/Slow DNS Server

Symptom: Browsing feels sluggish, pages take seconds to start loading, but once they start they load okay.

Diagnosis: Check /etc/resolv.conf for DNS servers on wrong subnets or that don't respond:

dig google.com @<suspect-server> +time=2

Fix: Switch to Cloudflare + Google DNS:

sudo nmcli connection modify "<profile-name>" ipv4.dns "1.1.1.1 8.8.8.8" ipv4.ignore-auto-dns yes
sudo nmcli connection down "<profile-name>" && sudo nmcli connection up "<profile-name>"

This is permanent and only affects the local machine.

WireGuard/VPN Throttling

Symptom: Speed is significantly slower with VPN active.

Diagnosis: Compare speed with and without VPN:

sudo nmcli connection down wg0
# re-run speed test

Fix: Disable VPN when not needed, or switch to a closer/faster VPN endpoint.

T-Mobile Home Internet Specific

Expected speeds: 33-245 Mbps depending on plan/signal
Gateway usually at 192.168.12.1
Check signal metrics (SINR, RSRP) at http://192.168.12.1
Good 5G: SINR > 10, RSRP > -90
Position gateway near a window, elevated, away from electronics

Post-Fix Verification

# Verify DNS settings persisted
cat /etc/resolv.conf

# Run speed test
curl -o /dev/null -w "Speed: %{speed_download} bytes/sec\n" https://speed.cloudflare.com/__down?bytes=10000000

# Should see 1.1.1.1 and 8.8.8.8 as nameservers
# Speed should be consistent with ISP plan

Eric's Setup (2026-03-16)

ISP: T-Mobile Home Internet
Connection: Wired ethernet (enp2s0f0) at 1000Mbps to T-Mobile gateway
Gateway IP: 192.168.12.1
DNS: Fixed to 1.1.1.1 / 8.8.8.8 (was using dead 192.168.1.104)
Speed after fix: ~126 Mbps