>> How to do a trace/kdump on pppd?
>
>Hrm. Kernel won't let you ktrace a set-uid binary, unless you are root.
>So make sure you are root. Also, I don't know about your system or anyone

su root, but made error: started ktrace on other machine as where i looked
for the file.
Now: kdump -dmR > /etc/kdump.txt

Does state a lot of errors(?):
  6384 pppd     RET   select -1 errno 4 Interrupted system call
  6384 pppd     RET   read -1 errno 35 Resource temporarily unavailable
  6384 pppd     RET   ioctl -1 errno 25 Inappropriate ioctl for device

and test again with ip-test: kill -15 pppd cause of ping in ip-test.
 Yes, with /etc/ppp/ip-test (ping peer/kill pppd) commented out.
 lcp-echo-interval 15
 lcp-echo-failure 15
 mtu 552
 mru 552

Line not droped, file 134k not always/mostly not transported, still
"network error: socket not connected".
Speed not lowered yet cause of problems login in on low speeds earlyer on.

kdump.txt not yet included, cause of time, volume and i can't read it/make
interpretations myself yet.
~n