Guys, seems I have found the conditions in which it happens. I have
successfully managed to *not* make it happen.

If you set the radius server IP property to match the public address,
this crash *will* happen, no matter what MTU or other encryption things
are set. PPP on Android doesn't have this problem.

Let's assume your PPTP server is at public IP 1.2.3.4, and such server
has an inside LAN IP of 192.168.79.1, you have two options:

A) You can leave the server IP property empty, in which case ppp will
work just fine !

B) You can set to a value, in order to do some manual routing on client
side later on by using that server IP.

But, if you set such property to 1.2.3.4 (matching exactly the public IP
on which the interface connects to) it will create this race condition
after a while and start sending crazy packets, crashing the ppp module.
Could be due to a looping-back broadcast.

Even though it might not be important for everyone, it shouldn't happen
that a property set on server side can crash a module on the client.
There should be a check.

Cheers,
Simone

-- 
You received this bug notification because you are a member of Desktop
Packages, which is subscribed to ppp in Ubuntu.
https://bugs.launchpad.net/bugs/1705391

Title:
  PPP crash after a while, start sending crazy packets

Status in ppp package in Ubuntu:
  New

Bug description:
  Hey guys, I have a very weird issue here. PPP works fine for 1-5
  minutes, then it hangs with CPU usage very high, and I noticed it
  start uploading insane (but fake) bytes to the tunnel. To do a simple
  test, I started watching a YouTube video, and when the problem started
  to happen:

  ppp0      Link encap:Point-to-Point Protocol  
            inet addr:172.16.99.9  P-t-P:xxx.xxx.xxx.xxx  Mask:255.255.255.255
            UP POINTOPOINT RUNNING NOARP MULTICAST  MTU:1400  Metric:1
            RX packets:26586 errors:0 dropped:0 overruns:0 frame:0
            TX packets:5921622 errors:0 dropped:0 overruns:0 carrier:0
            collisions:0 txqueuelen:3 
            RX bytes:35077655 (35.0 MB)  TX bytes:2885396935 (2.8 GB)

  Then it crashed, and VPN turned itself off. I tried everything: MTU,
  tunnel parameters etc. Please note I am a guy with 20+ years
  experience in networking and I own an IT company. This is definitely a
  BUG of PPP. It started happening since Ubuntu 16.04, before I never
  had this issue.

  
  Description:  Ubuntu 16.04.2 LTS
  Release:      16.04
  PPP:          2.4.7-1+2ubuntu1

  Cheers,
  Simone

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