Cry about...
MS-Windows Troubleshooting

---

error 733: could not agree on PPP control protocols

---

Symptom:

When trying to establish a VPN connection to a computer the following error is encountered:

Cause:

The client (i.e. your computer) and the server (i.e. the computer you are trying to establish a VPN connection to) cannot agree on a common set of PPP control protocols. This is a very generic error and can be caused by a number of things.

Possible Remedies:

• On the client disable the "Negotiate multi-link for single link connections" setting. To do this:
  1. Start > Settings > Control Panel
  2. Open "Network and dial-up Connections"
  3. Right click the VPN network connection giving the problem and select "Properties"
  4. On the "Networking" tab, click "Settings"
  5. Clear the check-box "Negotiate multi-link for single link connections"
• If the server is connected to the internet via a router then it may be that the router does not support VPN connections. Ask the server administrator to check that:
  1. The router supports "VPN pass-through" (be aware that different routers may use different terms). Other terms that are normally associated with this are: "IPSec" and "L2TP".
  2. The router is configured to pass through VPN connections to the necessary server.
     NOTE: It is not sufficient to simply forward ports 1723 and 47. Port 1723 needs to be forwarded, but what needs to be forwarded is IP Protocol 47 (GRE) not port 47. This is normally done via an explicit setting on the router. If the router does not appear to support this then investigate whether a bios upgrade is available for the router.
• Check that the server and client agree about who is assigning or specifying TCP/IP addresses. (It is common to allow the server to specify the TCP/IP address.)
• At the VPN server ensure that there are IP addresses available to allocate. The default setting for incoming TCP/IP is to "(o) Assign TCP/IP addresses automatically using DHCP" however if there is no DHCP server on the machine then instead select "(o) Specify TCP/IP addresses" and enter a suitable range.
• Check that the network protocol you are using (typically TCP/IP but could be NetBEUI) is also listed at the server end. (Note: Adding a protocol to an NT4 server will require a reboot to take effect.)

---

These notes have been tested with clients running Windows 2000 and Windows XP and with VPN servers on Windows NT 4, Windows 2000 and Windows 2003 Server.