nodemcu-firmware/docs/en/modules/mdns.md

# mDns Module

[Multicast DNS](https://en.wikipedia.org/wiki/Multicast_DNS) is used as part of Bonjour / Zeroconf. This allows system to identify themselves and the services that they provide on a local area network. Clients are then able to discover these systems and connect to them. 

## mdns.register()
Register a hostname and start the mDNS service. If the service is already running, then it will be restarted with the new parameters.

#### Syntax
`mdns.register(hostname, servicename, port [, attributes])`

#### Parameters
- `hostname` The hostname for this device. Alphanumeric characters are best.
- `servicename` The service name for this device. Alphanumeric characters are best. This will get prefixed with `_` and suffixed with `._tcp`
- `port` The port number for the primary service.
- `attributes` A optional table of up to 10 attributes to be exposed. The keys must all be strings.

#### Returns
`nil`

#### Errors
Various errors can be generated during argument validation. The NodeMCU must have an IP address at the time of the call, otherwise an error is thrown.

#### Example

    mdns.register("fishtank", "http", 80, { hardware='NodeMCU'})

Using `dns-sd` on OS X, you can see `fishtank.local` as providing the `_http._tcp` service. You can also browse directly to `fishtank.local`. In Safari you can get all the mDNS web pages as part of your bookmarks menu.

## mdns.close()
Shut down the mDNS service. This is not normally needed.

#### Syntax
`mdns.close()`

#### Parameters
none

#### Returns
`nil`