---
title: Network Error Logging
description: Network Error Logging (NEL) is a browser-based reporting system that allows users to report their own failures to an external endpoint. You can use Network Error Logging to gain insight into connectivity issues on the Internet to learn when and where an incident is happening, who is impacted, and how they are being impacted.
image: https://developers.cloudflare.com/core-services-preview.png
---

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# Network Error Logging

Network Error Logging (NEL) is a browser-based reporting system that allows users to report their own failures to an external endpoint. You can use Network Error Logging to gain insight into connectivity issues on the Internet to learn when and where an incident is happening, who is impacted, and how they are being impacted.

## The last mile

The last mile is the path from a user to the first point of ingress to the resource, whether that be a network like Cloudflare or directly to the origin server. The last mile is important because it is in the critical path of the request for a resource: if the last mile has issues, users cannot connect to their resources. When Network Error Logging is enabled, you can receive alerts about issues in the last mile — which are typically difficult to detect — to learn what the problem is and how to fix it.

![The last mile diagram, showing the steps involved in delivering data to a customer](https://developers.cloudflare.com/_astro/last-mile.oZJOfPRC_ZvDDO1.webp) 

## How NEL affects requests

The Report-To header is present in all requests to Cloudflare zones that have NEL enabled: 

```

report-to: {"group":"cf-nel","max_age":31536000,"endpoints":[{"url":"`[`https://a.nel.cloudflare.com/report?lkg-colo=lhr&lkg-time=1600338181`](https://gcp.nel.cloudflare.com/report?lkg-colo=lhr&lkg-time=1600338181&lkg-ip=1.1.1.1)`"}]}


```

A sample Network Error Report payload appears as follows:

```

{

  "age": 20,

  "type": "network-error",

  "url": "https://example.com/previous-page",

  "body": {

    "elapsed_time": 18,

    "method": "POST",

    "phase": "dns",

    "protocol": "http/1.1",

    "referrer": "https://example.com/previous-page",

    "sampling_fraction": 1,

    "server_ip": "",

    "status_code": 0,

    "type": "dns.name_not_resolved",

    "url": "https://example-host.com/"

  }

}


```

## Privacy

Cloudflare uses geolocation lookups to extract the following information from every client IP in a NEL report:

* Client ASN
* Client country
* Client metro area

Cloudflare uses internal lookups to associate the above data with a customer domain and customer account.

Cloudflare does not store any PII or user-specific data, and any IP data is only kept for the duration of the request as it is processed. After the report is processed through the NEL pipeline, all PII data is purged from the system.

The client IP address is only stored in volatile memory for the lifetime of the request to Cloudflare’s NEL endpoint (order of milliseconds) and is dropped immediately after the request completes. Cloudflare does not log the client IP address anywhere in the Network Error Logging pipeline. Customers can opt out of having their end users consume the NEL headers by [contacting Cloudflare support](https://developers.cloudflare.com/support/contacting-cloudflare-support/).

```json
{"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"item":{"@id":"/directory/","name":"Directory"}},{"@type":"ListItem","position":2,"item":{"@id":"/network-error-logging/","name":"Network Error Logging"}}]}
```

---

---
title: Get started
description: Network Error Logging is available to users on all plan types.
image: https://developers.cloudflare.com/core-services-preview.png
---

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# Get started

Network Error Logging is available to users on all plan types.

To enable Network Error Logging for Free and Pro zones:

1. In the Cloudflare dashboard, go to the **Account home** page.  
[ Go to **Account home** ](https://dash.cloudflare.com/?to=/:account/home)
2. Select **Network** and locate **Network Error Logging Monitoring**.
3. Select the toggle to enable Network Error Logging.

To enable this for Business and Enterprise, contact support or your account team.

```json
{"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"item":{"@id":"/directory/","name":"Directory"}},{"@type":"ListItem","position":2,"item":{"@id":"/network-error-logging/","name":"Network Error Logging"}},{"@type":"ListItem","position":3,"item":{"@id":"/network-error-logging/get-started/","name":"Get started"}}]}
```

---

---
title: How to
description: NEL reports show you why a request failed, the country a request failed from, and last mile network a request failed from, and the likely intended Cloudflare data center.
image: https://developers.cloudflare.com/core-services-preview.png
---

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# How to

Use NEL reports to view information such as:

* Why a request failed
* The country a request failed from
* The last mile network a request failed from
* The Cloudflare data center the request was most likely meant for
1. Log in to your Cloudflare dashboard.  
[ Go to **Account home** ](https://dash.cloudflare.com/?to=/:account/home)
2. Select **Analytics & Logs** \> **Edge Reachability**.

Click a tab under **Reachability summary** to view specific information related to your Origin ASN, Origin, IP, or data center. Hover over a location on the map to view the number of reachable requests.

Under **Reachability by data center**, click a location under Data Centers to filter reachability by a specific location.

To view the log fields available for NEL, refer to [NEL reports](https://developers.cloudflare.com/logs/logpush/logpush-job/datasets/zone/nel%5Freports/).

```json
{"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"item":{"@id":"/directory/","name":"Directory"}},{"@type":"ListItem","position":2,"item":{"@id":"/network-error-logging/","name":"Network Error Logging"}},{"@type":"ListItem","position":3,"item":{"@id":"/network-error-logging/how-to/","name":"How to"}}]}
```

---

---
title: Reference
description: If a user is able to connect to Cloudflare and the site they connect to has NEL enabled, Cloudflare passes back two headers to the browser indicating that they should report any network failures to an endpoint specified in the headers. The browser will operate as usual, and if something happens that prevents the browser from connecting to the site, the browser will log the failure as a report and send it to the endpoint.
image: https://developers.cloudflare.com/core-services-preview.png
---

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# Reference

If a user is able to connect to Cloudflare and the site they connect to has NEL enabled, Cloudflare passes back two headers to the browser indicating that they should report any network failures to an endpoint specified in the headers. The browser will operate as usual, and if something happens that prevents the browser from connecting to the site, the browser will log the failure as a report and send it to the endpoint.

Network Error Logging failures can occur for different reasons which are outlined below.

## Internet Service Provider (ISP) outage

An ISP outage appears to NEL users as failures from one particular last-mile network. By examining NEL data to look at the client autonomous system number (ASN) view, you can see which networks are causing the most impact.

For customers, this scenario appears as an influx of `tcp.timed_out errors`, as well as `tcp.failed`, `h2.protocol_error` and `h3.protocol_error`.

In the event of a last-mile outage, the best course of action is to contact the provider to investigate.

## Transit Flap

Transit flaps look like momentary outages caused by transits re-establishing BGP sessions.

To customers, this will appear as `tcp.timed_out` reports from a variety of ASNs over a short period of time. This could happen for several reasons:

* Maintenance in the transit network necessitated a reset of the session.
* Maintenance or reboots in Cloudflare necessitated a reset of the BGP session.
* Packet loss in the network caused the session to flap.

Heavy packet loss in the network will likely result in a series of flaps over time. Maintenance is typically one impact period that lasts no more than two minutes.

## Infrastructure outage

Infrastructure outages occur at shared peering points, such as Internet exchanges.

These outages appear to customers as an increase in `tcp.timed_out`, `tcp.failed`, and `tcp.aborted reports`. These failures will likely appear across multiple networks for an extended period of time.

Depending on the severity of the report volume, Cloudflare may declare an incident to track remediation. Alternatively, Cloudflare may deactivate peering from these shared points until the issue is resolved.

## Cloudflare outage

Cloudflare outages consist of issues within Cloudflare’s data-center fabric.

These outages appear to customers as an increase in `tcp.timed_out`, `tcp.failed`, and `tcp.aborted` reports and will likely appear across multiple networks for a short period of time.

By pivoting by data center, customers can track the impact across Cloudflare points of presence. Cloudflare-based incidents will always be tracked through a status page, which will indicate whether or not there are issues within the impacted region.

## Provider sending traffic through scrubbing center/blocking traffic

This type of outage manifests as TLS errors, such as `tls.cert.authority_invalid`, `tls.cert.name_invalid,` or others and may also present with `tcp.aborted errors`.

Customers may uncover this behavior by looking at which last-mile ASNs are displaying increased failures, as it will typically be only one.

Customers can seek remediation by contacting the provider that they believe is scrubbing their traffic.

## Certificate issues

Certificate issues are also detectable through NEL. The `TLS.version`, `cipher_mismatch`, or other errors may present across multiple ISPs in multiple Cloudflare locations.

If this is detected in NEL, the issue can be remediated by deploying new certificates or using [Cloudflare’s SSL management suite](https://developers.cloudflare.com/ssl/edge-certificates/advanced-certificate-manager/) to automatically deploy new certificates.

```json
{"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"item":{"@id":"/directory/","name":"Directory"}},{"@type":"ListItem","position":2,"item":{"@id":"/network-error-logging/","name":"Network Error Logging"}},{"@type":"ListItem","position":3,"item":{"@id":"/network-error-logging/reference/","name":"Reference"}}]}
```