pptp interview questions
Top pptp frequently asked interview questions
I try to create VPN client for ICS with VpnService, I read articles about ToyVpn and I know what I should create own PPTP tunnel but I can't fount any information about how I can create PPTP tunnel with mschapv2 authentication. After some researching I see what many applications use for creating PPTP tunnel C/C++ language. But I need do it on Java.
Have you any information or references how I can do it?
p.s. Please don't suggest about OpenVpn, I know it and I used it before, but now it is not right case
Source: (StackOverflow)
I know this has been ask before ,but most of them are 3 to 4 years ago with no definite answers.I would like to know if this is already posible as of 2015.
Source: (StackOverflow)
I've been editing androids toyvpn sample project for vpn and i got this one for my sample app
I know there is something wrong/missing with my code because when i manually set up the vpn via android settings, there are packets Receive that's why
i've been searching how to receive packets and i dont know how to get this working.
here is my source code that VCL that extends VpnService
import android.app.PendingIntent;
import android.net.VpnService;
import android.os.ParcelFileDescriptor;
import android.util.Log;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.net.InetSocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.DatagramChannel;
/**
* Created by Jameshwart Lopez on 8/18/15.
*/
public class VCL extends VpnService {
private static final String TAG = "VpnClientLibrary";
private Thread mThread;
private ParcelFileDescriptor mInterface;
private String mServerAddress;
private String mServerPort;
private PendingIntent mConfigureIntent;
private String mParameters;
//a. Configure a builder for the interface.
Builder builder = new Builder();
public void vclRun(){
try {
//a. Configure the TUN and get the interface.
mInterface = builder.setSession("thesessionname")
.addAddress("192.168.0.1",24)
.addDnsServer("8.8.8.8")
.addRoute("0.0.0.0", 0).establish();
//b. Packets to be sent are queued in this input stream.
FileInputStream in = new FileInputStream(mInterface.getFileDescriptor());
//b. Packets received need to be written to this output stream.
FileOutputStream out = new FileOutputStream(mInterface.getFileDescriptor());
// Allocate the buffer for a single packet.
ByteBuffer packet = ByteBuffer.allocate(32767);
//c. The UDP channel can be used to pass/get ip package to/from server
DatagramChannel tunnel = DatagramChannel.open();
// Connect to the server, localhost is used for demonstration only.
mServerAddress="";//some of the vpn ip address here
mServerPort="1723";
InetSocketAddress server = new InetSocketAddress(mServerAddress, Integer.parseInt(mServerPort) );
tunnel.connect(server);
// For simplicity, we use the same thread for both reading and
// writing. Here we put the tunnel into non-blocking mode.
tunnel.configureBlocking(false);
// Authenticate and configure the virtual network interface.
handshake(tunnel);
//d. Protect this socket, so package send by it will not be feedback to the vpn service.
protect(tunnel.socket());
int timer = 0;
//e. Use a loop to pass packets.
while (true) {
//get packet with in
//put packet to tunnel
//get packet form tunnel
//return packet with out
//sleep is a must
// Assume that we did not make any progress in this iteration.
boolean idle = true;
// Read the outgoing packet from the input stream.
int length = in.read(packet.array());
if (length > 0) {
// Write the outgoing packet to the tunnel.
packet.limit(length);
tunnel.write(packet);
packet.clear();
// There might be more outgoing packets.
idle = false;
// If we were receiving, switch to sending.
if (timer < 1) {
timer = 1;
}
}
// Read the incoming packet from the tunnel.
length = tunnel.read(packet);
if (length > 0) {
// Ignore control messages, which start with zero.
if (packet.get(0) != 0) {
// Write the incoming packet to the output stream.
out.write(packet.array(), 0, length);
}
packet.clear();
// There might be more incoming packets.
idle = false;
// If we were sending, switch to receiving.
if (timer > 0) {
timer = 0;
}
}
// If we are idle or waiting for the network, sleep for a
// fraction of time to avoid busy looping.
if (idle) {
Thread.sleep(100);
// Increase the timer. This is inaccurate but good enough,
// since everything is operated in non-blocking mode.
timer += (timer > 0) ? 100 : -100;
// We are receiving for a long time but not sending.
if (timer < -15000) {
// Send empty control messages.
packet.put((byte) 0).limit(1);
for (int i = 0; i < 3; ++i) {
packet.position(0);
tunnel.write(packet);
}
packet.clear();
// Switch to sending.
timer = 1;
}
// We are sending for a long time but not receiving.
//if (timer > 20000) {
// throw new IllegalStateException("Timed out");
//}
}
}
} catch (Exception e) {
// Catch any exception
e.printStackTrace();
} finally {
try {
if (mInterface != null) {
mInterface.close();
mInterface = null;
}
} catch (Exception e) {
}
}
}
private void handshake(DatagramChannel tunnel) throws Exception {
// To build a secured tunnel, we should perform mutual authentication
// and exchange session keys for encryption. To keep things simple in
// this demo, we just send the shared secret in plaintext and wait
// for the server to send the parameters.
// Allocate the buffer for handshaking.
ByteBuffer packet = ByteBuffer.allocate(1024);
// Control messages always start with zero.
String password = "";//vpn password here
packet.put((byte) 0).put(password.getBytes()).flip();
// Send the secret several times in case of packet loss.
for (int i = 0; i < 3; ++i) {
Log.e("packetsdata", packet.toString());
packet.position(0);
tunnel.write(packet);
}
packet.clear();
// Wait for the parameters within a limited time.
for (int i = 0; i < 50; ++i) {
Thread.sleep(100);
// Normally we should not receive random packets.
int length = tunnel.read(packet);
if (length > 0 && packet.get(0) == 0) {
configure(new String(packet.array(), 1, length - 1).trim());
return;
}
}
//throw new IllegalStateException("Timed out");
}
private void configure(String parameters) throws Exception {
// If the old interface has exactly the same parameters, use it!
if (mInterface != null) {
Log.i(TAG, "Using the previous interface");
return;
}
// Configure a builder while parsing the parameters.
Builder builder = new Builder();
for (String parameter : parameters.split(" ")) {
String[] fields = parameter.split(",");
try {
switch (fields[0].charAt(0)) {
case 'm':
builder.setMtu(Short.parseShort(fields[1]));
break;
case 'a':
builder.addAddress(fields[1], Integer.parseInt(fields[2]));
break;
case 'r':
builder.addRoute(fields[1], Integer.parseInt(fields[2]));
break;
case 'd':
builder.addDnsServer(fields[1]);
break;
case 's':
builder.addSearchDomain(fields[1]);
break;
}
} catch (Exception e) {
throw new IllegalArgumentException("Bad parameter: " + parameter);
}
}
// Close the old interface since the parameters have been changed.
try {
mInterface.close();
} catch (Exception e) {
// ignore
}
// Create a new interface using the builder and save the parameters.
mInterface = builder.setSession(mServerAddress)
.setConfigureIntent(mConfigureIntent)
.establish();
mParameters = parameters;
Log.i(TAG, "New interface: " + parameters);
}
}
this is how i use the class above
private Thread mThread;
/*
* Services interface
* */
@Override
public int onStartCommand(Intent intent, int flags, int startId) {
// Start a new session by creating a new thread.
mThread = new Thread(this, "VpnRunnable");
//start the service
mThread.start();
/*
*service is left "started" and will later be restarted by the system
* http://android-developers.blogspot.com.au/2010/02/service-api-changes-starting-with.html
*/
return START_STICKY;
}
@Override
public void onDestroy() {
if (mThread != null) {
mThread.interrupt();
}
super.onDestroy();
}
@Override
public synchronized void run() {
/*
* to run the vpn interface call the vclRun method inside VCL class
* */
this.vclRun();
}
Source: (StackOverflow)
I am a newbie to node.js and looking for some example code or pointers on connecting through PPTP to a private virtual ip address using VPN connection. I have a node.js server running on aws that currently uses udp to connect to a public ip address. However, this needs to be changed to tunnel into the private vpn.
I have the uid,pwd and apn for the vpn. What are the steps I would need to take to tunnel in, and then connect to the private ip?
Appreciate any tips you might have.
Thanks
M
Source: (StackOverflow)
Then trying to execute the following line:
ReadOnlyCollection<RasDevice> list = RasDevice.GetDevices();
I get a very non-helpful RasException (Error code 1070).
This is also thrown when executing
RasDevice.GetDeviceByName(...);
I have ran the application as administrator.
Is there a reason why enumerating the available devices may fail?
Source: (StackOverflow)
I'm trying to run pptpd container on a CoreOS system.
But I cannot load ppp kernel modules.
CoreOS doesn't allow me create directory.
Is it possible to install the missing modules?
# cat /etc/lsb-release
DISTRIB_ID=CoreOS
DISTRIB_RELEASE=681.2.0
DISTRIB_CODENAME="Red Dog"
DISTRIB_DESCRIPTION="CoreOS 681.2.0"
# ls /lib/modules/4.0.5/kernel/drivers/net/ppp
ls: cannot access /lib/modules/4.0.5/kernel/drivers/net/ppp: No such file or directory
# mkdir /lib/modules/4.0.5/kernel/drivers/net/ppp
mkdir: cannot create directory '/lib/modules/4.0.5/kernel/drivers/net/ppp': Read-only file system
Source: (StackOverflow)
every time I connect to my VPN, I should run
sudo ifconfig ppp0 mtu 1300
How could I make it permanent?
I'm using Ubuntu 14.04
Source: (StackOverflow)
i want to create app which can connect to VPN using PPTP, L2TP or OpenVPN, but i cant find any information about this. Only found infortmation about using IPSec and IKEv2 in ios 8 SDK.
Source: (StackOverflow)
I have a PPTP server running and I can connect to it from linux. When I try from windows 7 (2 instances tested) it fails. Here's the syslog for such a conn:
pptpd[540]: CTRL: Client 109.xxx.158.201 control connection started
pptpd[540]: CTRL: Starting call (launching pppd, opening GRE)
pppd[541]: Plugin radius.so loaded.
pppd[541]: RADIUS plugin initialized.
pppd[541]: Plugin radattr.so loaded.
pppd[541]: RADATTR plugin initialized.
pppd[541]: pppd 2.4.5 started by root, uid 0
pppd[541]: Using interface ppp0
pppd[541]: Connect: ppp0 <--> /dev/pts/1
pptpd[540]: GRE: Bad checksum from pppd.
pppd[541]: LCP: timeout sending Config-Requests
pppd[541]: Connection terminated.
pppd[541]: Modem hangup
pppd[541]: Exit.
pptpd[540]: GRE: read(fd=6,buffer=6075a0,len=8196) from PTY failed: status = -1 error = Input/output error, usually caused by unexpected termination of pppd, check option syntax and pppd logs
pptpd[540]: CTRL: PTY read or GRE write failed (pty,gre)=(6,7)
pptpd[540]: CTRL: Reaping child PPP[541]
pptpd[540]: CTRL: Client 109.xxx.158.201 control connection finished
I played with the mtu and ranged it from 900 to 1500 with no success. My pptp options:
name pptpd
refuse-pap
refuse-chap
refuse-mschap
require-mschap-v2
require-mppe-128
proxyarp
nodefaultroute
lock
nobsdcomp
ms-dns 10.10.0.1
noipx
mtu 1404
mru 1404
Remember! Linux client connects so ports and protocols should be enabled.
tcpdump -i eth0 port 1723 or proto 47 shows the following gist:
https://gist.github.com/ciokan/5595640
where 109.xxx.158.201 is me, the client.
No firewalls on client. Everything disabled. Im not a network admin and I can't understand jack from that tcpdump. HALP :)
Source: (StackOverflow)
I have a series of files I need to copy via SCP over a VPN from a remote linux server to a virtual linux server. The files are not large(4M-500M), but the file copy sometimes stalls. It seems that the network disconnect after that, because I could't receive any reply from a ping operation. And I have to restart the network service.
The virtual linux server's os is CentOS 6.4, and I use pptp as my vpn client.
From /var/log/messages I find messages like this:
pptp[14514]: anon log[decaps_gre:pptp_gre.c:414]: buffering packet 1181 (expecting 1043, lost or reordered)
pptp[14514]: anon log[decaps_gre:pptp_gre.c:414]: buffering packet 1182 (expecting 1043, lost or reordered)
pptp[14514]: anon log[decaps_gre:pptp_gre.c:414]: buffering packet 1183 (expecting 1043, lost or reordered)
...
rsyslogd-2177: imuxsock begins to drop messages from pid 14514 due to rate-limiting
rsyslogd-2177: imuxsock lost 130 messages from pid 14514 due to rate-limiting
...
anon log[decaps_gre:pptp_gre.c:414]: buffering packet 104763 (expecting 104761, lost or reordered)
anon log[decaps_gre:pptp_gre.c:414]: buffering packet 104764 (expecting 104761, lost or reordered)
anon log[decaps_gre:pptp_gre.c:414]: buffering packet 104765 (expecting 104761, lost or reordered)
...
anon warn[decaps_gre:pptp_gre.c:426]: discarding bogus packet 105383 (expecting 104814)
anon warn[decaps_gre:pptp_gre.c:426]: discarding bogus packet 105384 (expecting 104814)
anon warn[decaps_gre:pptp_gre.c:426]: discarding bogus packet 105385 (expecting 104814)
What I have tried so far:
both of them not worked.
Source: (StackOverflow)
I'm trying to implement a PPTP android client in java for a customer. The authentication is to be done via MSCHAP-v2 (Security not a concern at this level). My initial idea was that if I send a Start-Ctrl-Connection-Request to the server (via the default port 1723), it will reply with a Start-Ctrl-Connection-Reply followed by the 16-byte authentication challenge. I'm able to read a 156-byte Start-Ctrl-Connection-Reply as expected but there's no 16-byte challenge followed. Now it seems to me that I have to request for the challenge in some other way than sending control-connections. Any idea on how to request for the auth-challenge? Even the RFC regarding MS-CHAP does not give any clue on this. Or am I missing something?
Source: (StackOverflow)
I configured PPTP on my Raspberry Pi with Wheezy image following the guide given in webpage:
http://www.raspberrypihelp.net/tutorials/21-pptp-vpn-server-raspberry-pi
On completion of the configuration all worked well.
I then installed MYSQL, PHP, APACHE, & PHPMyAdmin, the install went well and all appears ok.
I used this site for guidance.
http://pimylifeup.com/raspberry-pi-mysql-phpmyadmin/
I then tried to reconnect to the PPTP running on the same unit.
Verifying username and password
I now get the error message
'Connecting to 192.168.10.18 using '
The remote connection was not made because the attempted VPN tunnels failed. The VPN server might be unreachable. If this connection is attempting to use an L2TP/IPsec tunnel, the security parameters required for IPsec negotiation might not be configured properl'y
If I do a port scan of the Pi port 1723 does not appear to be open.
Could be the Mysql install has closed the PPTP port?
I have run
sudo netstat -alpn |grep :1723
and the output says
tcp 0 0 0.0.0.0:1723 0.0.0.0:* LISTEN 2567/pptpd
Please can someone advise me of the best way to open the PPTP port?
Thanks
Source: (StackOverflow)
I installed a Ubuntu 14.10 virtual machine on Windows 8.1 using Vmware.
Ubuntu has access to Internet in the NAT mode. But I can't establish a pptp connection to a remote server from Ubuntu. Is this supported?
Source: (StackOverflow)
I cannot load some websites over PPTP but I can load these websites over L2TP.
For example, I cannot load http://speedtest.net over PPTP...
The MRU and MTU are the same for these two protocols : 1400.
The VPN servers are installed on my VPS.
Anyone experiencing the same issue ?
Is it related to the server or to the client ?
Thank you.
Source: (StackOverflow)