Why does my Comcast show 'Connected' but there's no internet access?

This classic symptom means your device successfully associated with the WiFi router but the router's WAN connection to Comcast's network is broken. The most common causes are: (1) the modem failed to obtain a public IP from Comcast's CMTS after a brief outage, (2) a DHCP lease expired and was not renewed, or (3) Comcast is experiencing a node-level outage in your area. Start by power-cycling the modem for 60 seconds, then the router, and check the Xfinity Status Center at xfinity.com/support/status for active outages in your ZIP code.

Why is my Comcast internet very slow even though it shows full bars?

Full WiFi signal bars measure radio signal strength between your device and router — they say nothing about the speed of the Comcast connection beyond the modem. Slow speeds with full bars are typically caused by: ISP network congestion during peak hours (6–10 PM), a mismatched modem plan (DOCSIS 3.0 modem on a Gigabit plan), WiFi channel congestion from neighboring networks, or background processes consuming bandwidth on your devices. Run a wired speed test at fast.com to isolate WiFi from WAN. If wired is also slow, call Comcast and request a line speed test from their NOC.

My Comcast internet is working on a wired connection but WiFi is not working — what do I do?

When wired works but WiFi does not, the Comcast line is fine. The issue is in the router's wireless radio. Try these steps in order: (1) Reboot the router. (2) Forget and reconnect to the WiFi network on your device. (3) Check that the router's 2.4 GHz or 5 GHz radio is enabled in the admin panel. (4) Reduce wireless channel width from 80 MHz to 40 MHz on 5 GHz if range is an issue. (5) Update router firmware. (6) If using an Xfinity Gateway in Bridge Mode, verify your third-party router is correctly configured for PPPoE or DHCP WAN type.

Comcast upload speed is very slow but download is fine — how do I fix this?

Asymmetric speed problems on Comcast (low upload, normal download) are often caused by: (1) High upstream power levels — check 192.168.100.1 and look for upstream power above 48 dBmV, which indicates a degraded coax drop or too many splitters. (2) DOCSIS channel bonding issues — a DOCSIS 3.0 modem with only 4 upstream channels will cap upload at roughly 120 Mbps. (3) Upload-heavy background apps (cloud backup, torrents) consuming all upstream bandwidth. Run 'netstat -e' on Windows or 'iftop' on Linux to identify culprits. If upstream power is high, call Comcast for a line inspection.

How do I tell if Comcast is having an outage versus a problem in my home?

Check the Xfinity Status Center at xfinity.com/support/status and enter your address or ZIP code. The Xfinity app also shows real-time outage alerts for your account. As a technical check, log into your modem's signal page at 192.168.100.1 — if you see multiple T3 or T4 timeout errors and abnormal signal levels, the problem is on Comcast's plant, not your equipment. You can also text 'OUTAGE' to 266278 (COMCAST) to get an automated outage status response for your service address.

Comcast WiFi Not Working: Complete Fix Guide for 'Connected But No Internet' & Slow Speed Issues

Fix Comcast WiFi not working, connected but no internet, and slow speeds in minutes. Step-by-step modem/router resets, DNS fixes, and advanced diagnostics.

Last updated: February 27, 2026

Last verified: February 27, 2026

2,563 words

Key Takeaways

Root Cause 1: IP address lease failure or DHCP conflict — your device connects to the router but the modem cannot obtain a valid public IP from Xfinity's CMTS, resulting in 'connected but no internet' status.
Root Cause 2: Signal degradation, channel congestion, or a provisioning issue on Comcast's side causes drastically reduced throughput, producing slow download/upload speeds even at full signal bars.
Root Cause 3: Router firmware bugs, misconfigured DNS servers, or a faulty coax splitter between the wall and modem interrupt connectivity entirely — especially after power outages or ISP maintenance windows.
Quick Fix Summary: Power-cycle modem → power-cycle router → release/renew IP on client → swap DNS to 8.8.8.8 or 1.1.1.1 → run signal level check at 192.168.100.1 → contact Xfinity support if upstream power exceeds 48 dBmV or downstream SNR falls below 30 dB.

Fix Approaches Compared
Method	When to Use	Time	Risk
Power-cycle modem + router	First step for any outage or slowness	3–5 min	None
Release/Renew IP (ipconfig /release + /renew)	Connected but no internet, 169.254.x.x address	1 min	None
Change DNS to 8.8.8.8 / 1.1.1.1	Slow browsing, intermittent drops, DNS timeout errors	2 min	None
Factory reset modem (via reset pinhole)	Persistent no-signal or provisioning failure after ISP confirms line is OK	10–15 min	Low — clears custom settings
Factory reset router	Router WiFi not working, repeated DHCP failures, firmware corruption	15–20 min	Medium — erases SSID/password/port rules
Check & replace coax splitter	Upstream power > 48 dBmV, downstream SNR < 30 dB, packet loss on modem signal page	20 min	Low
Swap WiFi channel (2.4 GHz → 5 GHz or vice versa)	Slow WiFi but wired connection is fast, crowded neighborhood	2 min	None
Contact Xfinity support / schedule tech visit	Node outage, persistent provisioning failure, line noise outside the home	30–60 min	None

Understanding the Error: Why Comcast WiFi Stops Working

When your Comcast (Xfinity) internet connection fails, it almost always falls into one of three categories:

Physical/Signal Layer — the coaxial cable, splitter, or modem itself is not receiving a clean RF signal from Comcast's Cable Modem Termination System (CMTS).
IP/DHCP Layer — the modem has a signal but cannot complete the DOCSIS provisioning handshake, so no public IP is assigned. Windows shows "Connected, no internet" (status code 0x274D / WSAEHOSTUNREACH). macOS shows the yellow triangle exclamation on the WiFi icon.
Application/DNS Layer — connectivity exists but DNS resolution fails, making every website appear broken. ping 8.8.8.8 succeeds but ping google.com times out.

Understanding which layer is broken cuts troubleshooting time from 45 minutes to under 10.

Step 1: Identify the Layer Affected

Check 1 — Wired vs. Wireless Plug a laptop directly into the Xfinity modem/gateway via Ethernet. If wired works but WiFi does not, the problem is in the router or wireless radio — not the Comcast line. If wired also fails, the issue is upstream.

Check 2 — Can you reach the modem's admin page? Open a browser and navigate to http://10.0.0.1 (Xfinity Gateway) or http://192.168.100.1 (standalone modem signal page). If the signal page loads, your local network is alive. Note the values:

Downstream Power: acceptable range −7 to +7 dBmV
Upstream Power: acceptable range 38–48 dBmV (above 48 = problem)
SNR (Signal-to-Noise Ratio): must be ≥ 30 dB for QAM256
T3/T4 Timeout Errors: any non-zero count indicates CMTS ranging failures

Check 3 — What IP does your device have? Run ipconfig (Windows) or ifconfig / ip addr (Linux/macOS). A 169.254.x.x address means DHCP failed entirely (APIPA fallback). A 192.168.x.x or 10.0.0.x address from the router but no internet means the router has a WAN IP problem.

Check 4 — Ping test sequence

ping 127.0.0.1        # loopback — confirms TCP/IP stack
ping 192.168.1.1      # default gateway — confirms LAN
ping 75.75.75.75      # Comcast DNS — confirms WAN routing
ping 8.8.8.8          # Google DNS — confirms public internet
ping google.com       # DNS resolution — confirms name lookup

The first failing hop tells you exactly where the break is.

Step 2: Fix Based on Layer

Fix A — Power Cycle (Fixes ~60% of Cases)

Unplug the coaxial cable from the modem for 10 seconds, then reconnect it. This clears any RF lock issues.
Unplug the modem's power adapter from the wall. Wait 60 full seconds (not 10 — the CMTS needs time to release the old lease).
Plug the modem back in. Wait 2–3 minutes for all lights to stabilize (Online light should be solid, not blinking).
Power-cycle the router (if separate from modem): unplug, wait 30 seconds, plug back in.
On client devices, disconnect and reconnect to WiFi.

Fix B — Release and Renew IP Address

If you see "Connected, no internet access" after the power cycle, force a new DHCP lease:

Windows (run as Administrator):

ipconfig /release
ipconfig /flushdns
ipconfig /renew

macOS: System Preferences → Network → WiFi → Advanced → TCP/IP → Click "Renew DHCP Lease"

Linux:

sudo dhclient -r eth0
sudo dhclient eth0

Fix C — Change DNS Servers

Comcast's default DNS (75.75.75.75, 75.75.76.76) occasionally experiences regional slowdowns. Replace them:

Google Public DNS: 8.8.8.8 and 8.8.4.4
Cloudflare DNS: 1.1.1.1 and 1.0.0.1

Set these in your router's WAN DNS settings rather than per device for network-wide effect. In the Xfinity Gateway admin panel: Gateway → Connection → Local IP Network → DNS.

Fix D — Fix Slow Upload/Download Speeds

Slow speeds on Comcast typically stem from:

WiFi interference: Use a WiFi analyzer app (NetSpot, WiFi Analyzer on Android) to find a less congested channel. Switch 2.4 GHz to channels 1, 6, or 11. Switch 5 GHz to channels 36, 40, 44, or 48.
QoS misconfig: Log into the Xfinity Gateway admin (10.0.0.1), navigate to Advanced → QoS and ensure no device is being throttled.
Modem plan mismatch: Run http://192.168.100.1 and verify your modem is provisioned at the correct tier. A DOCSIS 3.0 modem maxes out at ~300 Mbps; if you have a Gigabit plan, you need DOCSIS 3.1.
Duplex mismatch on wired ports: On Linux, run ethtool eth0 | grep Speed to confirm 1000Mb/s full-duplex. Force it if needed: sudo ethtool -s eth0 speed 1000 duplex full autoneg on.

Fix E — Comcast Business Router Troubleshooting

Business accounts with a separate Comcast Business router (e.g., Technicolor or Hitron device) have an additional admin portal. Access it at https://10.1.10.1 or the IP shown on the router label. Common business-specific issues:

Static IP misconfiguration: Verify the WAN IP, subnet mask, and gateway match the values in your Comcast Business service agreement exactly.
VLAN tagging: Some business handoffs require VLAN ID 100 or 101 on the WAN port — confirm with Comcast Business NOC at 1-800-391-3000.
Firewall ACL blocking outbound: Check Advanced Firewall → Outbound rules for over-restrictive ACLs blocking DNS (UDP 53) or HTTP/HTTPS.

Fix F — Factory Reset as Last Resort

If all else fails and Comcast confirms the line is clean:

Locate the Reset pinhole on the modem/gateway.
Insert a paperclip and hold for 10 seconds until the lights flash.
Wait 3–5 minutes for the device to re-provision from Comcast's servers.
Reconfigure your WiFi SSID and password.

⚠️ Note: After a factory reset, the modem must go through the DOCSIS ranging, registration, and IP provisioning sequence. This can take up to 10 minutes. Do not power-cycle during this window.

Step 3: Escalate to Comcast Support

If modem signal levels are abnormal (T3/T4 errors present, upstream > 48 dBmV), the problem is outside your home on Comcast's coaxial plant. Document the signal page values and call Xfinity support (1-800-XFINITY) or use the Xfinity app. Request a line check and, if needed, a technician visit to inspect the tap, drop amplifier, and ground block at the utility pole or pedestal.

Frequently Asked Questions

bash

#!/usr/bin/env bash
# ============================================================
# Comcast WiFi Diagnostic Script
# Works on Linux/macOS. Run with: bash comcast_diag.sh
# For Windows, see the PowerShell block at the bottom (comments)
# ============================================================

echo "======================================="
echo " Comcast WiFi Diagnostic Tool"
echo "======================================="
echo ""

# --- 1. Detect active network interface ---
IF=$(ip route get 1.1.1.1 2>/dev/null | awk '{print $5; exit}')
[ -z "$IF" ] && IF=$(route -n get default 2>/dev/null | awk '/interface/ {print $2}') # macOS fallback
echo "[INFO] Active interface: ${IF:-NOT DETECTED}"
echo ""

# --- 2. Show current IP configuration ---
echo "[STEP 1] Current IP configuration:"
if command -v ip &>/dev/null; then
  ip addr show "$IF" 2>/dev/null | grep -E 'inet |link/'
else
  ifconfig "$IF" 2>/dev/null | grep -E 'inet |ether'
fi
echo ""

# --- 3. Default Gateway ---
GW=$(ip route show default 2>/dev/null | awk '/default/ {print $3}' | head -1)
[ -z "$GW" ] && GW=$(netstat -nr 2>/dev/null | awk '/default|0\.0\.0\.0/ {print $2}' | head -1)
echo "[STEP 2] Default gateway: ${GW:-NOT FOUND}"
echo ""

# --- 4. Ping tests ---
ping_test() {
  local HOST=$1 LABEL=$2
  if ping -c 2 -W 2 "$HOST" &>/dev/null; then
    echo "  [PASS] $LABEL ($HOST) is reachable"
  else
    echo "  [FAIL] $LABEL ($HOST) is NOT reachable"
  fi
}

echo "[STEP 3] Connectivity ping tests:"
ping_test 127.0.0.1        "Loopback (TCP/IP stack)"
ping_test "$GW"            "Default Gateway (LAN)"
ping_test 75.75.75.75      "Comcast DNS (WAN)"
ping_test 8.8.8.8          "Google DNS (Public Internet)"
ping_test google.com       "google.com (DNS resolution)"
echo ""

# --- 5. DNS resolution test ---
echo "[STEP 4] DNS resolution test:"
if command -v dig &>/dev/null; then
  dig +short +time=3 google.com @75.75.75.75 && echo "  [PASS] Comcast DNS resolving"
  dig +short +time=3 google.com @8.8.8.8    && echo "  [PASS] Google DNS resolving"
elif command -v nslookup &>/dev/null; then
  nslookup google.com 75.75.75.75 2>&1 | tail -4
fi
echo ""

# --- 6. Traceroute to Comcast backbone ---
echo "[STEP 5] Traceroute (first 6 hops):"
if command -v traceroute &>/dev/null; then
  traceroute -m 6 -w 2 8.8.8.8 2>/dev/null
elif command -v tracepath &>/dev/null; then
  tracepath -m 6 8.8.8.8 2>/dev/null
fi
echo ""

# --- 7. Speed test via curl (quick throughput check) ---
echo "[STEP 6] Quick download speed test (10 MB file via Comcast CDN):"
curl -o /dev/null -s -w "Download speed: %{speed_download} bytes/sec\nTime: %{time_total}s\n" \
  "https://speed.xfinity.com/api/…" 2>/dev/null || \
curl -o /dev/null -s -w "Download speed: %{speed_download} bytes/sec\nTime: %{time_total}s\n" \
  "http://speedtest.tele2.net/10MB.zip"
echo ""

# --- 8. Check modem signal page (requires curl access to local modem) ---
echo "[STEP 7] Attempting to fetch modem signal page (192.168.100.1):"
SIGNAL=$(curl -s --connect-timeout 3 http://192.168.100.1/cmSignalData.htm 2>/dev/null | \
  grep -oE '(Power|SNR|Frequency)[^<]*' | head -20)
if [ -n "$SIGNAL" ]; then
  echo "$SIGNAL"
else
  echo "  [SKIP] Could not reach modem signal page. Try opening http://192.168.100.1 in browser."
fi
echo ""

# --- 9. Release and renew DHCP (optional) ---
echo "[STEP 8] To release/renew DHCP lease, run:"
echo "  sudo dhclient -r $IF && sudo dhclient $IF"
echo ""

# --- 10. Flush DNS cache ---
echo "[STEP 9] Flushing local DNS cache:"
if [[ "$OSTYPE" == "darwin"* ]]; then
  sudo dscacheutil -flushcache && sudo killall -HUP mDNSResponder && echo "  [DONE] macOS DNS cache flushed"
elif command -v systemd-resolve &>/dev/null; then
  sudo systemd-resolve --flush-caches && echo "  [DONE] systemd-resolved cache flushed"
elif command -v nscd &>/dev/null; then
  sudo service nscd restart && echo "  [DONE] nscd restarted"
fi
echo ""

echo "======================================="
echo " Diagnostic complete."
echo " If issues persist, check signal levels"
echo " at http://192.168.100.1 and contact"
echo " Xfinity support: 1-800-XFINITY"
echo "======================================="

# ============================================================
# WINDOWS (PowerShell) - Run as Administrator:
# ============================================================
# ipconfig /all
# ping 127.0.0.1; ping (Get-NetRoute -DestinationPrefix '0.0.0.0/0').NextHop
# ping 75.75.75.75; ping 8.8.8.8; ping google.com
# Resolve-DnsName google.com -Server 8.8.8.8
# tracert -h 6 8.8.8.8
# ipconfig /release; ipconfig /flushdns; ipconfig /renew
# Set-DnsClientServerAddress -InterfaceAlias 'Wi-Fi' -ServerAddresses ('8.8.8.8','8.8.4.4')
# netsh wlan show interfaces
# netsh winsock reset; netsh int ip reset  # then reboot
# ============================================================

Error Medic Editorial

The Error Medic Editorial team is composed of senior DevOps engineers, SREs, and network specialists with 10+ years of experience diagnosing ISP connectivity issues, DOCSIS infrastructure, and home/business network troubleshooting. Our guides are tested against real hardware and validated against official vendor documentation before publication.

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