PPTP Ping Notes

The error message you receive helps to determine what part of the PPTP connection to troubleshoot. When PPTP filtering is enabled, you might receive one of the following error messages:

Error 678: There is no answer

Error 650: The Remote Access Server is not responding

If you receive one of these error messages, disable PPTP filtering and then attempt to ping the PPTP server. To disable PPTP filtering, type the following command on the PPTP server:

   net stop raspptpf

You should now be able to ping the PPTP server over the Internet. If you still receive one of these error messages, the problem might not be a PPTP problem. Until you get replies from the server, you need to troubleshoot this issue as a normal connectivity problem.

If pinging the PPTP server across the Internet successfully returns with replies, the ISP or internal corporate network might not allow Generic Routing Encapsulation (GRE) packets or PPTP packets to go across the firewall or router.

GRE packets are commonly used internally as messages between routers. For example, an ISP might use GRE to distribute routing messages between its sites. For security or other reasons, this ability can be turned off to the outside Internet. You can resolve this problem by ensuring that Protocol 47 is open at the router or firewall. This protocol is required for PPTP to work correctly. In addition to GRE Protocol 47, Port 1723 must be enabled at all routers or firewalls between the PPTP client and server.

An example of a GRE-blocked PPTP call in a trace is shown below. In this case, the ISP uses GRE internally, but does not allow the protocol to be sent to any outside interfaces.

1- 5.364   00 E8 TCP	 ....S., len:

2- 5.614   E8 00 TCP	 .A..S., len:

3- 5.614   00 E8 TCP	 .A ., len: 0, seq: 168021101-168021101,
   ack:	460753,

4- 5.630   00 E8 TCP	 .AP..., len: 156, seq: 168021101-168021256,
   ack:	460753,

5- 6.130   E8 00 TCP	 .AP..., len:  156, seq:	460753-460908,
   ack:   168021257, win:

6- 6.145   00 E8 TCP	 .AP..., len:  168, seq: 168021257-168021424,
   ack:	460909,

7- 6.520   E8 00 TCP	 .AP..., len:   32, seq:	460909-460940,
   ack:	168021425, win:

8- 6.536   00 E8 TCP	 .AP..., len:   24, seq: 168021425-168021448,
   ack:	460941,

9- 6.536   20 20 LCP	 Config Req Packet, Ident = 0x00, Length = 17

10- 6.536  00 E8 LCP	 Config Req Packet, Ident = 0x00, Length = 17

11- 6.833  E8 00 ICMP	Destination Unreachable: 198.140.211.122
   See frame 10

12- 6.942  E8 00 TCP	 .A...., len:	0, seq:	460941-460941,
   ack:   168021449, win:
   

In frame 11, a reference states that the destination cannot be reached in frame 10. Looking closely at frame 10, you can see that this packet is actually a GRE packet:

+ FRAME: Base frame properties
+ ETHERNET: ETYPE = 0x0800 : Protocol = IP:  DOD Internet Protocol
+ IP: ID = 0xECB3; Proto = 0x2F; Len: 53
+ GRE: ..KS............ Length: 21, Call ID: 0  <<<--Shows that this is a
													 GRE packet.
+ PPP: Link Control Protocol Frame (0xC021)
+ LCP: Config Req Packet, Ident = 0x00, Length = 17

The IP address in the IP portion of this frame shows the IP address of the device that does not allow GRE packets past its interface.

Note

• Some ISPs or corporate firewalls do not allow incoming or outgoing GRE packets. In this case, you see the same "Destination Host Unreachable" packets in the trace, but there are no packets that drill down to GRE.

If you receive error 718, "the server has not responded," you might want to increase the number of attempts PPTP makes to transmit data.

You can make this change by editing the registry entry.

Caution

• Do not edit the registry directly unless you have no alternative. The registry editor bypasses standard safeguards, allowing settings that can degrade performance, damage your system, or even require you to reinstall Windows. You can safely alter most registry settings by using the programs in Control Panel or Microsoft Management Console (MMC). If you must edit the registry directly, back it up first. Read the Registry Editor Help for more information.

To increase PPTP data retransmissions

1. Run Registry Editor (Regedt32.exe).
   
   
2. Go to the following key in the registry:

   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Paramters

3. On the Edit menu, click Add Value and create the following entry. (If the entry already exists, double-click it to edit the value.)

   Value Name: PPTPTcpMaxDataRetransmissions

   Data Type: REG_DWORD

   Value range: 0 - 0xFFFFFFFF

   Default value: 9h

By default, this value is 9h. You might want to increase this value to 18h. It is not recommended to increase this value beyond 27h.

After each computer can connect to its ISP and ping the PPTP server, test logging on to the PPTP server.

Set up a Dial-Up Networking phone book entry to dial the IP address of the PPTP server. When you set up the phone book entry, enter the server IP address in place of a phone number. Dial using RASPPTPM.

If Dial-Up Networking dials but does not connect to the PPTP server, try restarting the Remote Access Server service.

To restart the Remote Access Server service

1. In Control Panel, double-click Services.
   
   
2. Locate the Remote Access Server service. Stop the service and then start the service.

PPTP requires that the connecting user account have dial-in permissions. Use the Remote Access Admin tool to verify that the user account has the appropriate dial-in permissions.

If a domain is present, the user might need domain permissions to connect to certain resources on the network.

Troubleshooting protocol issues

PPTP can use the NetBEUI, IPX/SPX-compatible, and TCP/IP protocols. The NetBEUI protocol requires the least amount of configuration. Connecting to the PPTP server requires that the client and server have a network protocol in common. Once connected, the PPTP server can act as NetBIOS gateway to the rest of the local area network.

When you are using the TCP/IP protocol, each client needs a unique IP address. IP addresses can be statically assigned to clients, supplied from a pool of IP addresses, or from a DHCP server.

PPTP Ping can be useful in troubleshooting connectivity issues with TCP/IP.

Avoid browsing My Network Places over a slow connection. Try connecting to the network resource directly.

To connect to a network resource directly

1. Click Start, and then click Run.
   
   
2. Type the following line, and then click OK:

   \\<server>\<share>

If you can connect using this method, the PPTP session is working properly and the issue is related to browsing.