The owner of any domain can configure subdomains as desired. This is achieved by creating a subdomain and setting its owner to the desired address - this can be the same as the owner of the parent domain, or any other address.
Additionally, web3.py provides a convenience method to create a subdomain, set a resolver, and configure an address record all at once:
In the common case that the name should be pointed to the owner's address, the second argument is optional.
Setting a Resolver
Before a newly created domain or subdomain can be used, a resolver address must be set. You may also want to do this if an updated resolver implementation is available that supports features that you want to make use of.
Most commonly, names are set to use a 'standard' resolver called the public resolver, which provides commonly-used functionality, but anyone may write and deploy their own special-purpose resolver; see the resolver interface definition for details.
On mainnet and the Kovan test network, 'resolver.eth' is configured to point to the latest deployed version of the public resolver, making it possible to easily configure a name to use the public resolver:
Not supported. web3.py automatically uses the public resolver when setup_address is called, and does not support setting custom resolvers.
Note that changing the resolver for a name will not automatically migrate records from the old resolver over; to do this you will need to follow the process outlined below for updating records.
To change the resources an address resolves to, it's necessary to update that name's records in its resolver.
Each resolver may specify its own mechanism for updating records, but a standard method is implemented by the public resolver and many others. Some libraries provide functionality for updating a resolver's records using this interface.
Some libraries - presently only ensjs, go-ens and web3.js - support updating other record types, such as content hashes and text records, using the same pattern. For example, to set or update a text record:
Public Resolver has multicall that permits users to set multiple records in a single operation. Read PublicResolver section for more detail.
Configuring Reverse Resolution
While 'regular' resolution involves mapping from a name to an address, reverse resolution maps from an address back to a name - or other metadata. ENS supports reverse resolution to allow applications to display ENS names in place of hexadecimal addresses.
Before this can be done, the owner of the address has to configure reverse resolution for their address. This is done by calling the claim() method on the reverse resolver, found at the special name 'addr.reverse'.
Most commonly this is accomplished via a user-interface such as the ENS Manager DApp. go-ens and web3.py also provide functionality for this: