Why does my Comcast WiFi show 'Connected, No Internet' even after restarting?

This usually means your device successfully associated with the WiFi SSID but the modem or gateway failed to obtain a WAN IP from Comcast's CMTS via DOCSIS. After restarting, if the Online LED on the gateway never turns solid, there is either a signal issue (check coaxial connection and signal levels at 192.168.100.1) or an active Comcast outage in your area. If the Online LED is solid but one device still shows 'no internet,' run ipconfig /release and ipconfig /renew on Windows or use dhclient -r && dhclient on Linux to get a fresh DHCP lease.

My Comcast internet is working on a wired connection but WiFi is not working — what's different?

When wired works but WiFi does not, the problem is isolated to the wireless radio layer. Common causes include: (1) the gateway's WiFi radio is disabled — check the WiFi LED and the admin UI at 10.0.0.1; (2) the device is associated to the wrong band — 2.4 GHz devices may receive a private IP but no default gateway if the DHCP pool is exhausted; (3) channel interference from neighbors — use a WiFi analyzer to identify a less-congested channel and set it manually in the gateway admin. A gateway reboot often re-initializes the radio and fixes the issue.

Why is my Comcast upload speed very slow even though download speed is normal?

Asymmetric slowness (slow upload, normal download) has three main causes: (1) Upstream channel power is too high (above 51 dBmV) indicating the modem is fighting to maintain upstream ranging — this requires a Comcast technician to check the tap/amplifier on the street; (2) Your plan tier — most residential Xfinity plans are DOCSIS 3.0 asymmetric, capping upload at 10–35 Mbps; (3) A device on your LAN is saturating the upstream with backup software (iCloud, Google Photos, Backblaze) — check by disconnecting all devices except one and running a speed test at speedtest.xfinity.com.

How do I fix Comcast internet that is connected but not getting full speed?

First, isolate the bottleneck: (1) Run a wired speed test directly from the gateway — if this hits near your subscribed speed, the loss is in your WiFi or LAN. (2) If wired is also slow, log into the modem admin at 192.168.100.1 and check signal levels. Low downstream power or SNR below 30 dB indicates a physical plant issue needing a tech visit. (3) For WiFi speed: manually set the channel, ensure your device supports 5 GHz (Wi-Fi 5 or Wi-Fi 6), and place the gateway in a central, elevated, unobstructed location. (4) Disable any VPN on the device, as some VPN tunnels cap throughput.

What do T3 and T4 timeout errors in the Comcast modem event log mean?

T3 timeouts mean the modem sent a ranging request to the CMTS (Comcast's cable modem termination system) but received no response within the timeout window — the upstream path is unreliable. T4 timeouts are more severe: the modem lost ranging lock entirely and had to re-initialize the DOCSIS registration process. You can view these at http://192.168.100.1 > Event Log. More than 5 T3 errors per hour or any T4 errors indicate degraded upstream signal, usually caused by a failing coaxial connector, a bad splitter, or an issue at the utility box on the street. Schedule a Comcast technician visit — this cannot be fixed from inside the house.

Comcast WiFi Not Working: Complete Troubleshooting Guide for 'Connected Without Internet' & Slow Speed Issues

Fix Comcast WiFi not working, connected but no internet, and slow speed issues in minutes. Step-by-step guide with real commands for home and business users.

Last updated: February 27, 2026

Last verified: February 27, 2026

2,610 words

Key Takeaways

Root Cause 1: IP address lease failure or DHCP conflict — your device connects to the router but never receives a valid public or private IP, causing 'connected without internet' errors.
Root Cause 2: Xfinity modem/gateway firmware issue, overheating, or signal degradation on the coaxial line — results in slow speeds (well below contracted plan) or full connectivity loss.
Root Cause 3: DNS misconfiguration or ISP-side outage — traffic cannot resolve hostnames even when the physical link appears active.
Quick Fix Summary: Power-cycle the modem and router (30-second full unplug), release/renew your IP, verify coaxial signal levels in the gateway admin UI (192.168.100.1), run an Xfinity speed test, and check the Xfinity Status Center for area outages before escalating to Tier 2 support.

Fix Approaches Compared
Method	When to Use	Time	Risk
Power-cycle modem + router	First step for any connectivity loss or slow speeds	2–5 min	None
Release & renew IP / flush DNS	Connected without internet, DNS errors, partial connectivity	1–2 min	Brief disconnect
Check & reseat coaxial cable	Slow download/upload, frequent drops, poor signal levels	5–10 min	None
Factory reset gateway	Persistent config corruption, forgotten admin password	15–30 min	Loses custom settings
Xfinity App / Status Center check	Suspected area outage, node issues	2 min	None
Change DNS to 8.8.8.8 / 1.1.1.1	Xfinity DNS slow or returning NXDOMAIN errors	2 min	Low
Split 2.4 GHz / 5 GHz SSIDs	Devices picking wrong band, inconsistent speeds	5 min	Low — brief WiFi drop
Disable Smart Bittorrent / QoS override	Upload speed very slow, throttling suspected	5 min	Low
Call Xfinity Tier 2 / schedule tech visit	Signal levels outside spec, modem errors persist after reset	30–60 min	None

Understanding the Error

When users report "Comcast WiFi not working" the complaint usually falls into one of three categories:

No internet at all — The Xfinity gateway is powered on and devices associate with the WiFi SSID, but Windows shows the yellow exclamation "No Internet Access" or macOS displays "Connected, no internet." The technical root cause is that the WAN interface on the gateway either has no IP from Comcast's DHCP server, or the downstream signal-to-noise ratio (SNR) has dropped below the minimum threshold required to pass traffic.
Connected but severely slow — Speedtest results are 10–50 % of the subscribed plan. This is almost always caused by: a degraded coaxial cable, a splitter with too much attenuation, WiFi channel congestion, or Xfinity throttling during peak hours.
Intermittent drops — The gateway resets itself every few hours. This typically points to T3/T4 timeout errors logged inside the modem's event log, meaning the modem is losing upstream ranging lock.

Step 1: Confirm Scope — Is It the WiFi or the Modem/WAN?

Before touching any settings, plug a laptop directly into the Xfinity gateway via Ethernet and run:

curl -s https://api.ipify.org && echo

If you get a valid public IP, the modem WAN side is working and the problem is WiFi-layer (radio, DHCP lease to your device, or DNS). If you get no response or a 192.168.100.x address, the modem itself has lost the WAN connection.

Check the modem admin page by navigating to http://192.168.100.1 in a browser while connected via Ethernet. Login with admin / password (default). Under Signal you will see downstream and upstream channel stats. Healthy values:

Downstream power: -7 to +7 dBmV
Downstream SNR: ≥ 33 dB (QAM256)
Upstream power: 38–48 dBmV

If upstream power reads above 51 dBmV or downstream SNR is below 30 dB, you have a physical plant/coaxial issue — a technician visit is required.

Step 2: Power-Cycle the Full Stack

This resolves the majority of "comcast no internet connection" complaints by forcing a fresh DHCP handshake between the modem and Comcast's CMTS:

Shut down all PCs and unplug any secondary routers.
Unplug the coaxial cable from the back of the Xfinity gateway.
Unplug the power cable from the gateway.
Wait 30 seconds (capacitors discharge, DHCP lease timer resets).
Reconnect the coaxial first, then plug in power.
Wait 3–5 minutes — watch the front LEDs: US/DS light should go solid before the Online light turns solid green/white.
Reconnect your router (if separate), wait another 60 seconds.

Step 3: Release and Renew IP — Fix 'Connected Without Internet'

If the gateway comes online but a specific device still shows "connected without internet," the device may hold a stale DHCP lease or have a self-assigned 169.254.x.x APIPA address.

Windows (run as Administrator):

ipconfig /release
ipconfig /flushdns
ipconfig /renew

macOS:

sudo ipconfig set en0 DHCP
sudo dscacheutil -flushcache
sudo killall -HUP mDNSResponder

Linux:

sudo dhclient -r eth0 && sudo dhclient eth0
sudo systemd-resolve --flush-caches

After renewal, confirm you have a valid RFC1918 address (typically 10.0.0.x or 192.168.1.x from your router, or 10.0.0.1 from Xfinity's gateway in bridge mode).

Step 4: Fix Slow Comcast Internet Speeds

4a. Eliminate the WiFi variable. Run a wired speed test first (Ethernet to gateway). If wired speed matches or is close to your subscribed tier, the bottleneck is WiFi — proceed to 4b. If wired is also slow, the issue is upstream with Comcast's network or your modem's signal levels.

4b. WiFi channel optimization. Xfinity gateways default to "Auto" channel selection, which often picks congested channels. Log into http://10.0.0.1 (Xfinity gateway default) > WiFi > Edit:

For 2.4 GHz: manually set channel to 1, 6, or 11.
For 5 GHz: set to 36, 40, 44, or 48 (lower 5 GHz channels avoid DFS events).

Use a channel scanner app (WiFi Analyzer on Android, or airport -s on macOS) to see which channels neighbors use.

4c. Separate your SSIDs. If your gateway broadcasts one combined SSID, older 2.4 GHz devices drag down the network. Log into the gateway admin and create separate SSIDs — name them HomeNetwork_2G and HomeNetwork_5G — then force fast devices to the 5 GHz network.

4d. Check for Xfinity Traffic Management. During peak hours (7–11 PM), Comcast may apply traffic management to heavy data users on certain plans. If upload speed is very slow, check your data usage in the Xfinity app. Users on plans with a 1.2 TB data cap who exceed it are throttled.

Step 5: Fix DNS — 'Comcast Connected But No Internet'

A common symptom: ping 8.8.8.8 succeeds (you have IP connectivity) but ping google.com fails with "could not resolve host." Xfinity's DNS servers (75.75.75.75 and 75.75.76.76) occasionally have propagation issues.

On your router: Change primary DNS to 1.1.1.1 (Cloudflare) and secondary to 8.8.8.8 (Google). Apply and reconnect devices.

On Windows directly:

netsh interface ip set dns "Wi-Fi" static 1.1.1.1
netsh interface ip add dns "Wi-Fi" 8.8.8.8 index=2

Step 6: Comcast Business Router Troubleshooting

For Comcast Business (CBiz) customers, the gateway is typically an SMC or Technicolor device with a static IP assigned. Additional checks:

Verify the Business Static IP is still live: curl -s https://api.ipify.org
Log into the CBiz admin portal to check for scheduled maintenance windows.
CBiz routers support an extended diagnostic page at http://192.168.0.1/RgDiagnostics.asp (model-dependent) showing T3/T4 timeout counts — more than 5 T3 timeouts per hour signals a plant issue.
If running a separate firewall/UTM downstream, confirm it is not blocking RFC1918 DHCP broadcasts — a common misconfiguration after firmware updates.

Step 7: Factory Reset as Last Resort

If all else fails and the gateway is not in a Comcast outage zone:

Locate the Reset pinhole on the back of the gateway.
Hold a paperclip in the hole for 10 seconds until the LED flashes.
Wait 5 minutes for the gateway to re-provision from Comcast's servers.
Reconfigure your WiFi SSID and password.

Warning: For Xfinity XB7/XB8 gateways running in bridge mode, a factory reset will re-enable the built-in router. You will need to re-enable bridge mode via the Xfinity app or xfinitygateway.com.

Step 8: Check for an Xfinity Outage

Before calling support:

Open the Xfinity app > Account > Check for outages.
Visit https://www.xfinity.com/support/status or https://downdetector.com/status/xfinity/.
Text "OUTAGE" to 266278 (COMCST) for automated status.

If an outage is confirmed, no local troubleshooting will restore the connection — wait for Comcast to resolve the node issue.

Frequently Asked Questions

bash

#!/usr/bin/env bash
# =============================================================
# Comcast / Xfinity WiFi & Internet Diagnostics Script
# Run with: bash comcast_diag.sh
# Compatible: Linux & macOS (adapt ipconfig calls for Windows)
# =============================================================

set -euo pipefail

echo "======================================="
echo " Comcast WiFi Diagnostics - $(date)"
echo "======================================="

# --- 1. Check default gateway ---
echo ""
echo "[1] Default Gateway Detection"
if command -v ip &>/dev/null; then
  GW=$(ip route | awk '/default/ {print $3; exit}')
else
  GW=$(route -n get default 2>/dev/null | awk '/gateway/ {print $2}')
fi
echo "    Gateway: ${GW:-NOT FOUND}"

# --- 2. Ping gateway (LAN reachability) ---
echo ""
echo "[2] LAN Gateway Ping Test"
if [ -n "${GW:-}" ]; then
  ping -c 4 -W 2 "$GW" | tail -2
else
  echo "    SKIP: No gateway found"
fi

# --- 3. Ping Comcast DNS ---
echo ""
echo "[3] Xfinity DNS Reachability (75.75.75.75)"
ping -c 4 -W 2 75.75.75.75 | tail -2

# --- 4. Ping public DNS (Cloudflare) ---
echo ""
echo "[4] Internet IP Reachability (1.1.1.1)"
ping -c 4 -W 2 1.1.1.1 | tail -2

# --- 5. DNS resolution test ---
echo ""
echo "[5] DNS Resolution Test"
if command -v dig &>/dev/null; then
  echo "    Via Xfinity DNS:"
  dig @75.75.75.75 google.com +short +time=3 | head -3
  echo "    Via Cloudflare DNS:"
  dig @1.1.1.1 google.com +short +time=3 | head -3
else
  nslookup google.com 75.75.75.75 | grep -E 'Address|Name'
fi

# --- 6. Current public IP ---
echo ""
echo "[6] External IP Address"
curl -s --max-time 5 https://api.ipify.org && echo ""

# --- 7. Traceroute to Comcast first hop ---
echo ""
echo "[7] Traceroute (first 8 hops)"
if command -v traceroute &>/dev/null; then
  traceroute -m 8 -w 2 8.8.8.8 2>&1 | head -12
else
  echo "    traceroute not installed — skipping"
fi

# --- 8. WiFi signal (Linux only) ---
echo ""
echo "[8] WiFi Signal Info (Linux)"
if command -v iwconfig &>/dev/null; then
  iwconfig 2>&1 | grep -E 'SSID|Signal|Bit Rate|Freq'
elif command -v iw &>/dev/null; then
  iw dev | grep -E 'ssid|signal|channel|width'
else
  echo "    Run on macOS: /System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resources/airport -I"
fi

# --- 9. Check DNS cache (Linux systemd) ---
echo ""
echo "[9] DNS Cache Stats"
if command -v systemd-resolve &>/dev/null; then
  systemd-resolve --statistics | grep -E 'Cache|Transactions'
else
  echo "    sudo dscacheutil -statistics  # macOS"
fi

# --- 10. Flush DNS ---
echo ""
echo "[10] Flush DNS Cache"
if command -v systemd-resolve &>/dev/null; then
  sudo systemd-resolve --flush-caches && echo "    DNS cache flushed (systemd)"
elif [ "$(uname)" = "Darwin" ]; then
  sudo dscacheutil -flushcache
  sudo killall -HUP mDNSResponder
  echo "    DNS cache flushed (macOS)"
fi

# --- 11. Release & Renew DHCP (Linux) ---
echo ""
echo "[11] DHCP Release & Renew (Linux only)"
IFACE=$(ip route | awk '/default/ {print $5; exit}')
if [ -n "${IFACE:-}" ] && command -v dhclient &>/dev/null; then
  echo "    Releasing $IFACE..."
  sudo dhclient -r "$IFACE" 2>/dev/null || true
  sleep 2
  echo "    Renewing $IFACE..."
  sudo dhclient "$IFACE" 2>/dev/null || true
  echo "    New IP:"
  ip addr show "$IFACE" | grep 'inet '
else
  echo "    SKIP: Not Linux or dhclient not found"
  echo "    Windows: ipconfig /release && ipconfig /renew"
  echo "    macOS:   sudo ipconfig set en0 DHCP"
fi

# --- 12. Final connectivity check ---
echo ""
echo "[12] Final HTTP Connectivity Check"
HTTP_CODE=$(curl -s -o /dev/null -w "%{http_code}" --max-time 5 https://www.google.com)
echo "    HTTP Status to google.com: $HTTP_CODE"
[ "$HTTP_CODE" = "200" ] && echo "    PASS: Internet connectivity confirmed" || echo "    FAIL: No HTTP connectivity"

echo ""
echo "======================================="
echo " Diagnostics Complete"
echo "======================================="

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, cloud, and on-premises connectivity issues. We write practical, command-line-first troubleshooting guides for IT professionals and technically-minded home users. Our articles are reviewed for accuracy against official vendor documentation and real-world lab testing.

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