SharePoint 2013 - 401 - Unauthorized: Access is denied due to invalid credentials.

I have a dev/lab environment with 4 virtual machines. I need to give my fellow developer access to my SharePoint 2013 demosite via IP-address (don't bother to ask why I'm using ip-adress. It's too complicated network setup to describe it here).

However i get this error when I try accessing the site using server IP 10.100.101.XX:80

I get same error locally and on other machines in the network when using IP.

Here's my setup: VMs: DC + SP2013-WFE + SQL2012 + Office Web App Server

SharePoint 2013 is RTM version. Web Application I'm trying to access is the default SharePoint - 80. I have DisableLoopbackCheck set. No alternate access mappings set so far. I can access the site on SharePoint 80 using the servernamehttp://devmachine  just fine. I tried same scenario on SharePoint 2010 version and using the server IP-adress and it worked fine. I've also tried different credentials. Only difference between SharePoint 2010 and 2013 setups I managed to find was the Authentication Method used by the default SharePoint - 80 web application. SharePoint 2010 default SharePoint - 80 Web Application usesClassic Mode Authenticaton. On 2013 server it is set as Claims Based Authentication.

I haven't played with Claims too much. Is it Claims Authentication that is preventing the access via IP or is it something else? Perhaps changes in SharePoint 2013 IIS websites? Please help me out with this problem!