The second part below neglects listing USEPEERDNS.
$ man pppd|grep -A 1 environment
peer (if any) are passed to the /etc/ppp/ip-up script in the environment vari‐
ables DNS1 and DNS2, and the environment variable USEPEERDNS will be set to 1.
In addition, pppd will create an /etc/ppp/resolv.conf file containing one or
--
output and error redirected to /dev/null, and with an environment that is empty except
for some environment variables that give information about the link. The environment
variables that pppd sets are: