Illegal Characters in Domain Names

[Mr Initial Man]

How many ISPs, firewalls, etc. will balk when you have an underscore in your domain name?

A friend who's a sysadmin doesn't think the domain name mr_initial_man.Furtopia.org will cause much trouble, another friend says because of the underscores, my domain name's going to block a lot of people from my website. Who is correct?

[bathurst_guy]

The underscore is an illegal character in domain names (but works elsewhere in URLs)You cannot have an underscore in a domain name, but you can in a subdomain.

[Mr Initial Man]

I know. It works fine in my other site. But I was wondering how many ISPs and firewalls will simply reject someone trying to access a site with an underscore in the domain name.

[dotancohen]

It's not spec. Don't use it.

[Mr Initial Man]

You still haven't answered my question.

[NogDog]

My web host provider will not accept an underscore in a domain name when checking to see if it's available.

[felgall]

Domain names that contain invalid characters don't exist. You can't create them in the first place and therefore no DNS needs to support them.

[NogDog]

Actaully, looking back at your post, I see that the underscores are only in the sub-domain. That's totally driven by your web host, and I don't think the DNS servers that route people to your site care what's in that, they're just concerned with the actual domain name, which is "Furtopia.org". As long as your web host doesn't care, then I don't think it matters. However, I'm not 100% sure about that.