What are the allowed characters in a subdomain?

Question

What characters are you allowed to use in a subdomain?

Example: for someSub.example.com the someSub portion.

I know you can use le

Answer 1

Technically William is right, and only letters, numbers and hyphen (-) are allowed in subdomains.

However: in practice, you will see that underscore (_) will also work in all major browsers, but this is not guaranteed. Some providers and other services may not allow you to set it in DNS.

If you set a wildcard in DNS it will resolve, then then it is up to the actual application to take it or ignore it.