PPP

PPP (Point-to-Point Protocol) is commonly used in establishing a direct connection between two networking nodes. It can provide connection authentication, transmission encryption, and compression.

Kernel
You need to activate the following kernel options:

Software
Portage knows the global USE flag ppp for enabling support for PPP in other packages. Enabling this USE flag will pull in automatically:

The USE flags of ppp are:

After setting this you want to update your system so the changes take effect: