Callback Control Protocol (CBCP)

Definition of CBCP in the Network Encyclopedia.

What is Callback Control Protocol (CBCP)?

Callback Control Protocol, also known as CBCP, is a protocol that is part of Microsoft’s implementation of the Point-to-Point Protocol (PPP). The Callback Control Protocol (CBCP) makes it possible for a PPP server to call back the remote dial-in client to complete initiation of a PPP dial-up session. Callback is a useful security feature for ensuring that dial-in clients are authentic.

How It Works: Callback Control Protocol

The CBCP is used during the third phase of establishing a PPP connection. After the PPP link is established using the Link Control Protocol (LCP) and the user’s credentials are authenticated using Microsoft Challenge Handshake Authentication Protocol (MS-CHAP) or some other authentication protocol supported by the client, the network access server (NAS) at the PPP service provider can optionally initiate a PPP callback control phase, provided that callback is configured on the server. The NAS and the PPP clients both disconnect from the PPP link, and the NAS calls the client back using the specified callback phone number. If the client responds, the link is reestablished; no further authentication is needed, and compatible network protocols are negotiated so that data transmission can begin.

CBCP is supported by the Remote Access Service (RAS) for Microsoft Windows NT.

CBCP as an extra layer of Remote Access Security

Use CBCP as an extra layer of remote access security to secure corporate networks based on Windows NT. If Windows 95 or Windows 98 clients have trouble connecting to Windows NT remote access servers when CBCP is configured on the servers, try checking the ppplog.txt file on the Windows 95 or Windows 98 clients.