# Config override (advanced config)

A config override is a change to one Nebula setting, such as the [MTU](/docs/glossary/mtu/) or the log level, that replaces Managed Nebula's default for a host, for every host with a [tag](/docs/glossary/tag/), or for a whole [network](/docs/glossary/network/). The [admin panel](/docs/glossary/admin-panel/) calls these settings advanced config. The API and the Terraform provider call them config overrides.

Managed Nebula writes each host's Nebula config for you, so overrides are only for hosts that need something different, like debug logging while you troubleshoot or a filter that keeps Docker addresses out of lighthouse updates. You can set them in three places:

- **Host**: on the [Hosts](https://admin.defined.net/hosts) page, open the host, click the edit (pencil) button, and choose the **Advanced** tab.
- **Tag**: in the tag's **Host advanced config** section on the [Tags](https://admin.defined.net/tags) page.
- **Network**: in the network's **Host advanced config** section under [Settings > Networks](https://admin.defined.net/settings/networks).

Each setting is worked out on its own, and the most specific value wins: a host's own value beats a tag's, and a tag's beats the network's. When two of a host's tags set the same setting, the tag higher in the tag order wins. A value replaces the one below it whole, so lists aren't merged. Overrides apply to hosts, lighthouses, and relays you run, not to [managed lighthouses](/docs/glossary/managed-lighthouse/).

[DNClient](/docs/glossary/dnclient/) picks up most changes without a restart. A few settings, including MTU, are read only when Nebula starts, and the admin panel tells you when a change needs a DNClient restart.

In the API, each override is a `key`, such as `logging.level`, and a JSON `value`, and each request replaces a host's, tag's, or network's whole list. See [Configuring advanced host settings](/docs/guides/advanced-host-config/) for where each setting lives and common tasks, and [Config override keys](/docs/api/config-override-keys/) for every key and its allowed values.