Point to Point Tunnel Protocol (PPTP)

Document revision 1.8 (27-Mar-2003)
This document applies to MikroTik RouterOS v2.7

Table of Contents

Summary

PPTP (Point to Point Tunnel Protocol) supports encrypted tunnels over IP. The MikroTik RouterOS implementation includes support fot PPTP client and server.

General applications of PPTP tunnels:

Each PPTP connection is composed of a server and a client. The MikroTik RouterOS may function as a server or client or, for various configurations, it may be the server for some connections and client for other connections. For example, the client created below could connect to a Windows 2000 server, another MikroTik Router, or another router which supports a PPTP server.

Specifications

Packages required : ppp
License required : Basic (DEMO license is limited to 4 tunnels)
Home menu level : /interface pptp-server, /interface pptp-client
Protocols utilized : PPTP (RFC2637)
Hardware usage: not significant

Related Documents

Software Package Installation and Upgrading
IP Addresses and Address Resolution Protocol (ARP)
Authentication, Authorization and Accounting
Ethernet over IP (EoIP) Tunnel Interface

Description

PPTP is a secure tunnel for transporting IP traffic using PPP. PPTP encapsulates PPP in virtual lines that run over IP. PPTP incorporates PPP and MPPE (Microsoft Point to Point Encryption) to make encrypted links. The purpose of this protocol is to make well-managed secure connections between routers as well as between routers and PPTP clients (clients are available for and/or included in almost all OSs including Windows).

PPTP includes PPP authentication and accounting for each PPTP connection. Full authentication and accounting of each connection may be done through a RADIUS client or locally.

MPPE 40bit RC4 and MPPE 128bit RC4 encryption are supported.

PPTP traffic uses TCP port 1723 and IP protocol GRE (Generic Routing Encapsulation, IP protocol ID 47), as assigned by the Internet Assigned Numbers Authority (IANA). PPTP can be used with most firewalls and routers by enabling traffic destined for TCP port 1723 and protocol 47 traffic to be routed through the firewall or router.

PPTP connections may be limited or impossible to setup though a masqueraded/NAT IP connection. Please see the Microsoft and RFC links at the end of this section for more information.

PPTP Client Setup

Submenu level : /interface pptp-client

Property Description

name (name; default: pptp-out1) - interface name for reference
mtu (integer; default: 1460) - Maximum Transmit Unit. The optimal value is the MTU of the interface the tunnel is working over decreased by 40 (so, for 1500-byte ethernet link, set the MTU to 1460 to avoid fragmentation of packets)
mru (integer; default: 1460) - Maximum Receive Unit. The optimal value is the MTU of the interface the tunnel is working over decreased by 40 (so, for 1500-byte ethernet link, set the MRU to 1460 to avoid fragmentation of packets)
connect-to (IP address)- the IP address of the PPTP server to connect to
user (string)- user name to use when logging on to the remote server
password (string; default: "")- user password to use when logging to the remote server
profile (name; default: default) - profile to use when connecting to the remote server
add-default-route (yes | no; default: no) - whether to use the server which this client is connected to as its default router (gateway)

Example

To set up PPTP client named test2 using username john with password john to connect to the 10.1.1.12 PPTP server and use it as the default gateway:
[admin@MikroTik] interface pptp-client> add name=test2 connect-to=10.1.1.12 \
\... user=john add-default-route=yes password=john
[admin@MikroTik] interface pptp-client> print
Flags: X - disabled, R - running
  0 X  name="test2" mtu=1460 mru=1460 connect-to=10.1.1.12 user="john"
       password="john" profile=default add-default-route=yes


[admin@MikroTik] interface pptp-client> enable 0

Monitoring PPTP Client

Command name : /interface pptp-client monitor

Property Description

Statistics:

uptime (time) - connection time displayed in days, hours, minutes, and seconds
encoding (string) - encryption and encoding (if asymmetric, separated with '/') being used in this connection
status (string) - status of the client:

  • Dialing attempting to make a connection
  • Verifying password... - connection has been established to the server, password verification in progress
  • Connected self-explanatory
  • Terminated interface is not enabled or the other side will not establish a connection

    Example

    Example of an established connection:
    [admin@MikroTik] interface pptp-client> monitor test2
          uptime: 4h35s
        encoding: MPPE 128 bit, stateless
          status: Connected
    [admin@MikroTik] interface pptp-client>
    

    PPTP Server Setup

    Submenu level : /interface pptp-server server
    [admin@MikroTik] interface pptp-server server> print
                enabled: no
                    mtu: 1460
                    mru: 1460
         authentication: mschap2
        default-profile: default
    [admin@MikroTik] interface pptp-server server>
    

    Description

    The PPTP server supports unlimited connections from clients. For each current connection, a dynamic interface is created.

    Property Description

    enabled (yes | no; default: no) - defines whether PPTP server is enabled or not
    mtu (integer; default: 1460) - Maximum Transmit Unit. The optimal value is the MTU of the interface the tunnel is working over decreased by 40 (so, for 1500-byte ethernet link, set the MTU to 1460 to avoid fragmentation of packets)
    mru (integer; default: 1460) - Maximum Receive Unit. The optimal value is the MTU of the interface the tunnel is working over decreased by 40 (so, for 1500-byte ethernet link, set the MTU to 1460 to avoid fragmentation of packets)
    authentication (multiple choice: pap | chap | mschap1 | mschap2; default: mschap2) - authentication algorithm
    default-profile (name; default: default) - default profile to use

    Example

    To enable PPTP server:
    [admin@MikroTik] interface pptp-server server> set enabled=yes
    [admin@MikroTik] interface pptp-server server> print
                enabled: yes
                    mtu: 1460
                    mru: 1460
         authentication: mschap2
        default-profile: default
    [admin@MikroTik] interface pptp-server server>
    

    PPTP Server Users

    Submenu level : /interface pptp-server

    Description

    There are two types of items in PPTP server configuration - static users and dynamic connections. A dynamic connection can be established if the user database or the default-profile has its local-address and remote-address set correctly. When static users are added, the default profile may be left with its default values and only P2P user (in /ppp secret) should be configured. Note that in both cases P2P users must be configured properly.

    Property Description

    name - interface name
    user - the name of the user that is configured statically or added dynamically

    Statistics:

    mtu - shows (cannot be set here) client's MTU
    client-address - shows (cannot be set here) the IP of the connected client
    uptime - shows how long the client is connected
    encoding (string) - encryption and encoding (if asymmetric, separated with '/') being used in this connection

    Example

    To add a static entry for ex1 user:
    [admin@MikroTik] interface pptp-server> add user=ex1
    [admin@MikroTik] interface pptp-server> print
    Flags: X - disabled, D - dynamic, R - running
      #     NAME                 USER         MTU   CLIENT-ADDRESS  UPTIME   ENC...
      0  DR <pptp-ex>            ex           1460  10.0.0.202      6m32s    none
      1     pptp-in1             ex1
    [admin@MikroTik] interface pptp-server>
    
    In this example an already connected user ex is shown besides the one we just added.

    PPTP Router-to-Router Secure Tunnel Example

    The following is an example of connecting two Intranets using an encrypted PPTP tunnel over the Internet.

    There are two routers in this example:

    Each router is connected to a different ISP. One router can access another router through the Internet.

    On the PPTP server a user must be set up for the client:

    [admin@HomeOffice] ppp secret> add name=ex service=pptp password=lkjrht
    local-address=10.0.103.1 remote-address=10.0.103.2
    [admin@HomeOffice] ppp secret> print detail
    Flags: X - disabled
      0   name="ex" service=pptp caller-id="" password="lkjrht" profile=default
          local-address=10.0.103.1 remote-address=10.0.103.2 routes==""
    
    [admin@HomeOffice] ppp secret>
    

    Then the user should be added in the PPTP server list:

    [admin@HomeOffice] interface pptp-server> add user=ex
    [admin@HomeOffice] interface pptp-server> print
    Flags: X - disabled, D - dynamic, R - running
      #     NAME                 USER         MTU   CLIENT-ADDRESS  UPTIME   ENC...
      0     pptp-in1             ex
    [admin@HomeOffice] interface pptp-server>
    

    And finally, the server must be enabled:

    [admin@HomeOffice] interface pptp-server server> set enabled=yes
    [admin@HomeOffice] interface pptp-server server> print
                enabled: yes
                    mtu: 1460
                    mru: 1460
         authentication: mschap2
        default-profile: default
    [admin@HomeOffice] interface pptp-server server>
    

    Add a PPTP client to the RemoteOffice router:

    [admin@RemoteOffice] interface pptp-client> add connect-to=192.168.80.1 user=ex \
    \... password=lkjrht disabled=no
    [admin@RemoteOffice] interface pptp-client> print
    Flags: X - disabled, R - running
      0  R name="pptp-out1" mtu=1460 mru=1460 connect-to=192.168.80.1 user="ex"
           password="lkjrht" profile=default add-default-route=no
    
    
    [admin@RemoteOffice] interface pptp-client>
    

    Thus, a PPTP tunnel is created between the routers. This tunnel is like an Ethernet point-to-point connection between the routers with IP addresses 10.0.103.1 and 10.0.103.2 at each router. It enables 'direct' communication between the routers over third party networks.

    To route the local Intranets over the PPTP tunnel add these routes:

    [admin@HomeOffice] > ip route add dst-address 10.150.1.0/24 gateway 10.0.103.2
    [admin@RemoteOffice] > ip route add dst-address 10.150.2.0/24 gateway 10.0.103.1
    

    On the PPTP server it can alternatively be done using routes parameter of the user configuration:

    [admin@HomeOffice] ppp secret> print detail
    Flags: X - disabled
      0   name="ex" service=pptp caller-id="" password="lkjrht" profile=default
          local-address=10.0.103.1 remote-address=10.0.103.2 routes==""
    
    [admin@HomeOffice] ppp secret> set 0 routes="10.150.1.0/24 10.0.103.2 1"
    [admin@HomeOffice] ppp secret> print detail
    Flags: X - disabled
      0   name="ex" service=pptp caller-id="" password="lkjrht" profile=default
          local-address=10.0.103.1 remote-address=10.0.103.2
          routes="10.150.1.0/24 10.0.103.2 1"
    
    [admin@HomeOffice] ppp secret>
    

    Test the PPTP tunnel connection:

    [admin@RemoteOffice]> /ping 10.0.103.1
    10.0.103.1 pong: ttl=255 time=3 ms
    10.0.103.1 pong: ttl=255 time=3 ms
    10.0.103.1 pong: ttl=255 time=3 ms
    ping interrupted
    3 packets transmitted, 3 packets received, 0% packet loss
    round-trip min/avg/max = 3/3.0/3 ms
    

    Test the connection through the PPTP tunnel to the LocalHomeOffice interface:

    [admin@RemoteOffice]> /ping 10.150.2.254
    10.150.2.254 pong: ttl=255 time=3 ms
    10.150.2.254 pong: ttl=255 time=3 ms
    10.150.2.254 pong: ttl=255 time=3 ms
    ping interrupted
    3 packets transmitted, 3 packets received, 0% packet loss
    round-trip min/avg/max = 3/3.0/3 ms
    

    To bridge a LAN over this secure tunnel, please see the example in the 'EoIP' section of the manual. To set the maximum speed for traffic over this tunnel, please consult the 'Queues' section.

    Connecting a Remote Client via PPTP Tunnel

    The following example shows how to connect a computer to a remote office network over PPTP encrypted tunnel giving that computer an IP address from the same network as the remote office has (without need of bridging over eoip tunnels)

    Please, consult the respective manual on how to set up a PPTP client with the software You are using.

    The router in this example:

    The client computer can access the router through the Internet.

    On the PPTP server a user must be set up for the client:

    [admin@RemoteOffice] ppp secret> add name=ex service=pptp password=lkjrht
    local-address=10.150.1.254 remote-address=10.150.1.2
    [admin@RemoteOffice] ppp secret> print detail
    Flags: X - disabled
      0   name="ex" service=pptp caller-id="" password="lkjrht" profile=default
          local-address=10.150.1.254 remote-address=10.150.1.2 routes==""
    
    [admin@RemoteOffice] ppp secret>
    

    Then the user should be added in the PPTP server list:

    [admin@RemoteOffice] interface pptp-server> add name=FromLaptop user=ex
    [admin@RemoteOffice] interface pptp-server> print
    Flags: X - disabled, D - dynamic, R - running
      #     NAME                 USER         MTU   CLIENT-ADDRESS  UPTIME   ENC...
      0     FromLaptop           ex
    [admin@RemoteOffice] interface pptp-server>
    

    And the server must be enabled:

    [admin@RemoteOffice] interface pptp-server server> set enabled=yes
    [admin@RemoteOffice] interface pptp-server server> print
                enabled: yes
                    mtu: 1460
                    mru: 1460
         authentication: mschap2
        default-profile: default
    [admin@RemoteOffice] interface pptp-server server>
    

    Finally, the proxy APR must be enabled on the 'Office' interface:

    [admin@RemoteOffice] interface ethernet> set Office arp=proxy-arp
    [admin@RemoteOffice] interface ethernet> print
    Flags: X - disabled, R - running
      #    NAME                 MTU   MAC-ADDRESS       ARP
      0  R ToInternet           1500  00:30:4F:0B:7B:C1 enabled
      1  R Office               1500  00:30:4F:06:62:12 proxy-arp
    [admin@RemoteOffice] interface ethernet>
    

    PPTP Setup for Windows

    Microsoft provides PPTP client support for Windows NT, 2000, ME, 98se, and 98. Windows 98se, 2000, and ME include support in the Windows setup or automatically install PPTP. For 95, NT, and 98, installation requires a download from Microsoft. Many ISPs have made help pages to assist clients with Windows PPTP installation.

    http://www.real-time.com/Customer_Support/PPTP_Config/pptp_config.html
    http://www.microsoft.com/windows95/downloads/contents/WUAdminTools/S_WUNetworkingTools/W95WinsockUpgrade/Default.asp

    Sample instructions for PPTP (VPN) installation and client setup Windows 98se

    If the VPN (PPTP) support is installed, select 'Dial-up Networking' and 'Create a new connection'. The option to create a 'VPN' should be selected. If there is no 'VPN' options, then follow the installation instructions below. When asked for the 'Host name or IP address of the VPN server', type the IP address of the router. Double-click on the 'new' icon and type the correct user name and password (must also be in the user database on the router or RADIUS server used for authentication).

    The setup of the connections takes nine seconds after selection the 'connect' button. It is suggested that the connection properties be edited so that 'NetBEUI', 'IPX/SPX compatible', and 'Log on to network' are unselected. The setup time for the connection will then be two seconds after the 'connect' button is selected.

    To install the 'Virtual Private Networking' support for Windows 98se, go to the 'Setting' menu from the main 'Start' menu. Select 'Control Panel', select 'Add/Remove Program', select the 'Windows setup' tab, select the 'Communications' software for installation and 'Details'. Go to the bottom of the list of software and select 'Virtual Private Networking' to be installed.

    Troubleshooting

    Additional Resources

    Links for PPTP documentation:

    http://msdn.microsoft.com/library/backgrnd/html/understanding_pptp.htm
    http://support.microsoft.com/support/kb/articles/q162/8/47.asp
    http://www.ietf.org/rfc/rfc2637.txt?number=2637
    http://www.ietf.org/rfc/rfc3078.txt?number=3078
    http://www.ietf.org/rfc/rfc3079.txt?number=3079


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