The current version of dip-uri supports PPP in that it will execute the pppd process when you execute \mode PPP\. However, there are many options which are needed for the proper operation of pppd. Since dip does not pass these to the program, they must be stored in the /etc/ppp/options file.
The dip program controls the establishment of the SLIP link. It controls the SLIP link with the aid of slattach, ifconfig, and route. These programs may be used to establish a SLIP link. They are not useful for the establishment of a PPP link.
The dip program may be used to dial the telephone and start the PPP software on the remote system. It is best used in this mode as the parameter to the \connect\ option. However, you have the option to use dip to control the link. It is not important how pppd be executed to run the PPP link. It is only important that it be executed as it is a mandatory program for the PPP protocol.
While this is not a FAQ for dip, there is a common problem with dip and pppd. The dip process has the absolute pathname to the pppd process embedded within it. Until recently, the location for pppd was /usr/lib/ppp/pppd. It has moved to the /usr/sbin/pppd location. So, if you are unable to get dip to start pppd then check the pathnames in dip.
Additional information about the dip process is in the Net-2-HOWTO document.
The location of the pppd program file is stored within dip.
The 2.1 version of pppd was stored in /usr/lib/ppp/pppd. The 2.2 version has moved to the more \standard\ location of /usr/sbin/pppd. That is well and good. However, the problem is that now dip has the wrong location for pppd. When it attempts to run the pppd process as you do \mode ppp\, the dip program attempts to run the pppd program and it can\t because it isn\ there.
You can temporarily make a symbolic link from the /usr/lib/ppp/pppd location to the /usr/sbin/pppd file. However, a better solution is to rebuild the dip program so that it knows that pppd is at /usr/sbin/pppd.