SharePoint 2013 Licensing - On Premises

SharePoint 2013 Licensing has 2 Models :

1)      Server + CAL

2)      Server Only

Depends on the type of environment we have to choose among the 2 options.

 Intranet :

In intranet scenario we have will to go for option 1 means we have to go for Server + CAL.
 
Server à depends on how many servers running in each farm, license will be calculated according to no of instances(servers) in farm. If no of servers are 4 in the SP Farm, need to buy 4 server license.

CALà this depends no of users who are accessing the SharePoint portals , 500 are users accessing SP portal then need to buy 500 CAL.

4 servers in farm and 500 users accessing the SP services based on this we have to go for option 1 ,means you have to buy server + CAL.

 Extranet:

People whose user accounts are not of AD, users belongs to third party LDAPs, and looking for access SP Site ,in this case no CALS are required.
Server license (Option 2) permits the external users without any additional CALs.

Internet:

Intranet users who wants to access the portals from internet , in this scenario also, need to choose OPTION 1 and no CALS are required.

Reference Link : https://www.microsoft.com/en-us/Licensing/learn-more/brief-sharepoint-server-2013.aspx