Troubleshooting

Use this page to diagnose and resolve common issues with Cloudflare Tunnel. For tunnel health monitoring, logs, and metrics, refer to Monitoring.

Connection errors

When cloudflared cannot reach the Cloudflare network, it logs specific error messages that indicate whether the issue is DNS resolution, QUIC (UDP), or TCP connectivity.

DNS resolution failures

edge discovery: error looking up Cloudflare edge IPs

ERR edge discovery: error looking up Cloudflare edge IPs: the DNS query failed
    error="lookup _v2-origintunneld._tcp.argotunnel.com on 172.19.64.1:53: no such host"

This error means the DNS resolver configured on your machine cannot resolve the SRV records that cloudflared uses to discover the Cloudflare Tunnel destination IPs. Common causes include corporate DNS resolvers that strip or block SRV records, and DNS resolvers that return compressed SRV records.

To diagnose:

On the cloudflared host machine, run:

dig SRV _v2-origintunneld._tcp.argotunnel.com

If you receive SERVFAIL, NXDOMAIN, or an empty answer, test against Cloudflare's public resolver:

dig SRV _v2-origintunneld._tcp.argotunnel.com @1.1.1.1

To resolve:

• If 1.1.1.1 returns results but your local resolver does not, configure the host to use Cloudflare DNS (1.1.1.1) or another public resolver.
• If neither resolver returns results, your firewall is likely blocking outbound DNS queries (UDP port 53). Work with your network administrator to allow DNS traffic.

DNS query failed ... i/o timeout

ERR edge discovery: error looking up Cloudflare edge IPs: the DNS query failed
    error="lookup _v2-origintunneld._tcp.argotunnel.com on 127.0.0.11:53:
    read udp 127.0.0.1:53467->127.0.0.11:53: i/o timeout"

This variant means DNS queries from cloudflared are being blocked or dropped entirely — the resolver never responds. This is common in container environments (Docker, Kubernetes) where the internal DNS resolver (127.0.0.11) is unreachable or misconfigured.

To resolve:

• In Docker, verify your container's DNS configuration (/etc/resolv.conf). You can override the resolver with --dns 1.1.1.1 when running the container.
• In Kubernetes, verify the kube-dns or CoreDNS service is running and reachable from the pod.
• On the cloudflared host, verify that the resolver listed in /etc/resolv.conf is reachable and responding to queries.

QUIC handshake timeout

Failed to dial a quic connection

ERR Failed to dial a quic connection error="failed to dial to edge with quic:
    timeout: handshake did not complete in time" connIndex=0 ip=198.41.192.227
INF Retrying connection in up to 2s connIndex=0 ip=198.41.192.227

This error means cloudflared resolved the Cloudflare Tunnel destination IPs but could not complete a QUIC handshake over UDP port 7844. Your network or firewall is blocking outbound UDP traffic to Cloudflare.

cloudflared retries with exponential backoff (2, 4, 8, 16, 32, up to 64 seconds). After exhausting retries, it falls back to HTTP/2 over TCP:

INF Switching to fallback protocol http2 connIndex=0

If the fallback also fails, you will see a TCP connection timeout error.

To diagnose:

On the cloudflared host machine, test connectivity on port 7844:

nc -uvz -w 3 198.41.192.227 7844

Replace 198.41.192.227 with the IP shown in your error message. If the port is closed or blocked by a firewall, the command will return Connection refused or time out.

To resolve:

• Allow outbound UDP traffic to port 7844 on your firewall or security group. Refer to the full list of IPs and ports.
• If you cannot open UDP, cloudflared will fall back to HTTP/2 over TCP automatically. You can also force HTTP/2 by setting the --protocol http2 run parameter, but QUIC is recommended for better performance.

TCP connection timeout

DialContext error: dial tcp ... i/o timeout

ERR Unable to establish connection with Cloudflare edge
    error="DialContext error: dial tcp 198.41.200.43:7844: i/o timeout" connIndex=0
ERR Serve tunnel error
    error="DialContext error: dial tcp 198.41.200.43:7844: i/o timeout" connIndex=0

This error means cloudflared cannot reach Cloudflare over TCP port 7844. If you also see the QUIC handshake timeout above it, both UDP and TCP are blocked — the tunnel cannot connect at all.

To diagnose:

As a quick test, run:

curl -v https://region1.v2.argotunnel.com:7844

If the connection hangs, traffic is being dropped between your host and Cloudflare.

To test if cloudflared can connect on port 7844, run:

nc -vz -w 3 198.41.200.43 7844

Replace 198.41.200.43 with the IP shown in your error message. If the port is closed or blocked by a firewall, the command will return Connection refused or time out.

To resolve:

• Allow outbound TCP traffic to port 7844 to the Cloudflare Tunnel IP ranges.
• If your environment blocks port 7844 entirely (both UDP and TCP), the tunnel cannot function. Work with your network administrator to allow outbound traffic on this port.

I see cloudflared service is already installed.

If you see this error when installing a remotely-managed tunnel, ensure that no other cloudflared instances are running as a service on this machine. Only a single instance of cloudflared may run as a service on any given machine. Instead, add additional routes to your existing tunnel. Alternatively, you can run sudo cloudflared service uninstall to uninstall cloudflared.

I see An A, AAAA, or CNAME record with that host already exists.

If you are unable to save your tunnel's public hostname, choose a different hostname or delete the existing DNS record. Check the DNS records for your domain from the Cloudflare dashboard ↗.

Tunnel credentials file does not exist or is not a file.

If you encounter the following error when running a tunnel, double check your config.yml file and ensure that the credentials-file points to the correct location. You may need to change /root/ to your home directory.

cloudflared tunnel run

2021-06-04T06:21:16Z INF Starting tunnel tunnelID=928655cc-7f95-43f2-8539-2aba6cf3592d
Tunnel credentials file '/root/.cloudflared/928655cc-7f95-43f2-8539-2aba6cf3592d.json' doesn't exist or is not a file

My tunnel fails to authenticate.

To start using Cloudflare Tunnel, a super administrator in the Cloudflare account must first log in through cloudflared login. The client will launch a browser window and prompt the user to select a hostname in their Cloudflare account. Once selected, Cloudflare generates a certificate that consists of three components:

• The public key of the origin certificate for that hostname
• The private key of the origin certificate for that domain
• A token that is unique to Cloudflare Tunnel

Those three components are bundled into a single PEM file that is downloaded one time during that login flow. The host certificate is valid for the root domain and any subdomain one-level deep. Cloudflare uses that certificate file to authenticate cloudflared to create DNS records for your domain in Cloudflare.

The third component, the token, consists of the zone ID (for the selected domain) and an API token scoped to the user who first authenticated with the login command. When user permissions change (if that user is removed from the account or becomes an admin of another account, for example), Cloudflare rolls the user's API key. However, the certificate file downloaded through cloudflared retains the older API key and can cause authentication failures. The user will need to login once more through cloudflared to regenerate the certificate. Alternatively, the administrator can create a dedicated service user to authenticate.

I see an error: x509: certificate signed by unknown authority.

This means the origin is using a certificate that cloudflared does not trust. For example, you may get this error if you are using SSL/TLS inspection in a proxy between your server and Cloudflare. To resolve:

• Add the certificate to the system certificate pool.
• Use the --origin-ca-pool flag and specify the path to the certificate.
• Use the --no-tls-verify flag to stop cloudflared checking the certificate for a trust chain.

I see an error 1033 when attempting to run a tunnel.

A 1033 error indicates your tunnel is not connected to Cloudflare's network because Cloudflare's network cannot find a healthy cloudflared instance to receive the traffic.

First, review whether your tunnel is listed as Active on the Cloudflare One ↗ dashboard by going to Networks > Connectors > Cloudflare Tunnels or run cloudflared tunnel list. If the tunnel is not Active, review the following and take the action necessary for your tunnel status:

Status	Meaning	Recommended Action
Healthy	The tunnel is active and serving traffic through four connections to the Cloudflare global network.	No action is required. Your tunnel is running correctly.
Inactive	The tunnel has been created (via the API or dashboard) but the cloudflared connector has never been run to establish a connection.	Run the tunnel as a service (recommended) or use the cloudflared tunnel run command on your origin server to connect the tunnel to Cloudflare. Refer to substep 6 of step 1 in the Create a Tunnel dashboard guide or step 4 in the Create a Tunnel API guide.
Down	The tunnel was previously connected but is currently disconnected because the cloudflared process has stopped.	1. Ensure the cloudflared service or process is actively running on your server. 2. Check for server-side issues, such as the machine being powered off, an application crash, or recent network changes.
Degraded	The cloudflared connector is running and the tunnel is serving traffic, but at least one individual connection has failed. Further degradation in tunnel availability could risk the tunnel going down and failing to serve traffic.	1. Review your cloudflared logs for connection failures or error messages. 2. Investigate local network and firewall rules to ensure they are not blocking connections to the Cloudflare Tunnel IPs and ports.

For more information, refer to the comprehensive list of Cloudflare 1xxx errors.

I see a 502 Bad Gateway error when connecting to an HTTP or HTTPS application through tunnel.

A 502 Bad Gateway error with Unable to reach the origin service. The service may be down or it may not be responding to traffic from cloudflared on a tunnel route means the tunnel itself is connected to the Cloudflare network, but cloudflared cannot reach the origin service defined in your ingress rule. Unlike error 1033, which indicates the tunnel is not connected to Cloudflare, a 502 error indicates the problem is between cloudflared and your local service.

To identify the specific cause, review your Tunnel logs for error-level messages. Common causes include:

Origin service is not running

If the origin service has stopped or never started, cloudflared logs will show an error similar to:

error="dial tcp [::1]:8080: connect: connection refused"

To resolve, verify the service is running and listening on the expected port:

curl -v http://localhost:8080

If the service is not running, start or restart it. You can confirm the service is listening by running ss -tlnp | grep <PORT> (Linux) or lsof -iTCP -sTCP:LISTEN -nP | grep <PORT> (macOS).

Origin service URL uses the wrong protocol

If the origin expects HTTPS but the tunnel route specifies http://, or vice versa, cloudflared logs will show an error similar to:

error="net/http: HTTP/1.x transport connection broken: malformed HTTP response \"\x15\x03\x01\x00\x02\x02\""

To resolve, update the service URL in your tunnel route to match the protocol your origin expects. For example, change http://localhost:8080 to https://localhost:8080. If you are using a locally-managed tunnel, update your ingress rule in the configuration file.

Origin service URL points to the wrong port

If the port in your tunnel route does not match the port your service is listening on, cloudflared will log a connection refused error for that port. Double-check the service URL in your ingress rule and compare it against the port your application is bound to.

Origin uses a certificate that cloudflared does not trust

If the origin presents a TLS certificate that cloudflared cannot verify, the logs will show an error similar to:

error="x509: certificate is valid for example.com, not localhost"

This commonly occurs when the origin uses a self-signed certificate or when an SSL/TLS inspection proxy sits between cloudflared and the origin.

To resolve, use one of the following approaches:

• Set originServerName to the hostname on the origin certificate in your tunnel route. If you are using a locally-managed tunnel, here is an example of a configuration file:

  ingress:
    - hostname: app.example.com
      service: https://localhost:443
      originRequest:
        originServerName: app.example.com

• Provide the CA certificate using caPool:

  ingress:
    - hostname: app.example.com
      service: https://localhost:443
      originRequest:
        caPool: /path/to/ca-cert.pem

• As a last resort, disable TLS verification with noTLSVerify. This is not recommended for production environments.

  ingress:
    - hostname: app.example.com
      service: https://localhost:443
      originRequest:
        noTLSVerify: true

I see ERR_TOO_MANY_REDIRECTS when attempting to connect to an Access self-hosted app.

This error occurs when cloudflared does not recognize the SSL/TLS certificate presented by your origin. To resolve the issue, set the origin server name parameter to the hostname on your origin certificate. Here is an example of a locally-managed tunnel configuration:

ingress:
  - hostname: test.example.com
    service: https://localhost:443
    originRequest:
      originServerName: test.example.com

cloudflared access shows an error websocket: bad handshake.

This means that your cloudflared access client is unable to reach your cloudflared tunnel origin. To diagnose this, look at the cloudflared tunnel logs. A common root cause is that the cloudflared tunnel is unable to proxy to your origin (for example, because the ingress is misconfigured, the origin is down, or the origin HTTPS certificate cannot be validated by cloudflared tunnel). If cloudflared tunnel has no logs, it means Cloudflare's network is not able to route the websocket traffic to it.

There are several possible root causes behind this error:

• Your cloudflared tunnel is either not running or not connected to Cloudflare's network.
• WebSockets are not enabled.
• Your Cloudflare account has Universal SSL enabled but your SSL/TLS encryption mode is set to Off (not secure). To resolve, go to SSL/TLS > Overview in the Cloudflare dashboard and set your SSL/TLS encryption mode to Flexible, Full, or Full (strict).
• Your requests are blocked by Super Bot Fight Mode. To resolve, make sure you set Definitely automated to Allow in the bot fight mode settings.
• Your SSH or RDP Access application has the Binding Cookie enabled. To disable the cookie, go to Access controls > Applications and edit the application settings.
• One or more Workers routes are overlapping with the tunnel hostname, and the Workers do not properly handle the traffic. To resolve, either exclude your tunnel from the Worker route by not defining a route that includes the tunnel's hostname, or update your Worker to only handle specific paths and forward all other requests to the origin (for example, by using return fetch(req)).

Tunnel connections fail with SSL error.

If cloudflared returns error error="remote error: tls: handshake failure", check to make sure the hostname in question is covered by a SSL certificate. If using a multi-level subdomain, an advanced certificate may be required as the Universal SSL will not cover more than one level of subdomain. This may surface in the browser as ERR_SSL_VERSION_OR_CIPHER_MISMATCH.

Tunnel connections fail with Too many open files error.

If your Cloudflare Tunnel logs return a socket: too many open files error, it means that cloudflared has exhausted the open files limit on your machine. The maximum number of open files, or file descriptors, is an operating system setting that determines how many files a process is allowed to open. To increase the open file limit, you will need to configure ulimit settings on the machine running cloudflared.

I see failed to sufficiently increase receive buffer size in my cloudflared logs.

This buffer size increase is reported by the quic-go library ↗ leveraged by cloudflared ↗. You can learn more about the log message in the quic-go repository ↗. This log message is generally not impactful and can be safely ignored when troubleshooting. However, if you have deployed cloudflared within a unique, high-bandwidth environment then buffer size can be manually overridden for testing purposes.

To set the maximum receive buffer size on Linux:

1. Create a new file under /etc/sysctl.d/:

   sudo vi 98-core-rmem-max.conf

2. In the file, define the desired buffer size:

   net.core.rmem_max=2500000

3. Reboot the host machine running cloudflared.

4. To validate that these changes have taken effect, use the grep command:

   sudo sysctl -a | grep net.core.rmem_max

   net.core.rmem_max = 2500000

Cloudflare Tunnel is buffering my streaming response instead of streaming it live.

Proxied traffic through Cloudflare Tunnel is buffered by default unless the origin server includes the Content-Type: text/event-stream response header. This header tells cloudflared to stream data as it arrives instead of buffering the entire response.

How do I contact support?

For the fastest possible troubleshooting, ensure your support ticket includes comprehensive details. The more context you provide, the faster your issue can be identified and resolved.

To ensure efficient resolution when contacting support, include as much relevant detail as possible in your ticket:

• Context: Briefly describe the scenario or use case (for example, where the user was, what they were trying to do).

• Reproduction steps: Describe the steps you took to reproduce the issue during troubleshhooting.

• Timestamps: Be specific and include the exact time and time zone when the issue occurred.

• Troubleshooting attempts: Outline any troubleshooting steps or changes already attempted to resolve the issue.

• Tunnel logs: Include the logs from your local machine.
• Tunnel diagnostic logs: Include tunnel diagnostic logs.

Write a detailed ticket to resolve your issue faster

Avoid vague descriptions and include scenario, timestamps, and steps taken to troubleshoot the issue. Refer to the following example:

Acme Corp attempted to establish a tunnel connection on October 30, 2025, at approximately 3:45 PM UTC. DNS resolution and TCP connectivity tests passed, but the cloudflared daemon logs showed failed to sufficiently increase receive buffer size errors. The tunnel diagnostic logs collected at 3:50 PM UTC are attached, along with the output from the DNS and network connectivity pre-checks.