MS Callback

Description

The MS Callback feature provides client-server callback services for Microsoft Windows 95 and Microsoft Windows NT clients. MS Callback supports the Microsoft Callback Control Protocol (MSCB). MSCB is Microsoft's proprietary protocol that is used by Windows 95 and Windows NT clients. MS Callback supports negotiated PPP Link Control Protocol (LCP) extensions initiated and agreed upon by the Microsoft client. MS Callback is added to existing PPP Callback functionality. Therefore, if you configure your Cisco access server to perform PPP Callback using Cisco IOS Release 11.3(2)T or later, MS Callback is automatically available.

MS Callback supports AAA security models using a local database or AAA server.

MSCB uses LCP callback options with suboption type 6. The Cisco MS Callback feature supports clients with a user-specified callback number and server specified (preconfigured) callback number.

MS Callback does not affect non-Microsoft machines that implement standard PPP LCP extensions as described in RFC 1570. In this scenario, MS Callback is transparent.

List of Terms

callback--Callback functionality identifies a client-server relationship between the two ends of a point-to-point connection. The calling end of the initial call is the callback client. The answering end of the initial call is the callback server.

Callback Control Protocol (CBCP)--The proprietary Callback Control Protocol implemented by Microsoft.

Link Control Protocol (LCP)--A protocol that establishes, configures, and tests data link connections used by PPP.

PPP callback--A service that provides a client-server relationship between the end points of a point-to-point connection. PPP callback allows a router to request that a dial-up peer router call back. The callback feature can be used to control access and toll costs between routers.

Microsoft Callback Control Protocol (MSCB)--A proprietary protocol used by Microsoft clients running Windows 95 and Windows NT.

point-to-point protocol (PPP)--As described in RFC 1661, PPP encapsulates network layer protocol information over point-to-point links.

Public Switch Telephone Network (PSTN)--Generic term used for telephone networks and services.

Restrictions

The following are restrictions of the Microsoft Callback Server feature:

MS Callback is only supported for authorized clients using either CHAP or PAP.
MS Callback is only supported on PSTN and ISDN links.
MS Callback is only supported for IP.

Platforms

This feature is supported on these platforms:

Cisco 1000 series
Cisco 1600 series
Cisco 2500 series
Cisco 3600 series
Cisco 4000 series
Cisco 4500 series
Cisco 5200
Cisco 5300
Cisco 7200 series
Cisco 7500 series

Prerequisites

The following conditions must exist before you implement the Microsoft Callback Server feature:

The Cisco access server and client must be configured for PPP and PPP Callback.
The router or access server must be configured to use CHAP or PAP authorization.

Configuration Tasks

If you configure the Cisco access server for PPP Callback using Cisco IOS Release 11.3(2)T, MS Callback is enabled by default. You do not need to configure additional parameters on the Cisco access server.

Configuration Example

Configuration examples for PPP Callback are documented in the Dial Solutions Configuration Guide for Cisco IOS Release 11.3.

Command Reference

There are no new or modified commands required to configure this feature. However, refer to the "Debug Commands" section in this feature document for modified debug information.

Debug Commands

The debug ppp command is revised to add the cbcp keyword which supports MSCB. Only the information that applies to debug ppp cbcp is provided. Refer to the Cisco IOS Release 11.3 Debug Command Reference for complete debug ppp information.

debug ppp cbcp

Use the debug ppp EXEC command with the cbcp keyword to display information specific to the exchange of PPP connections using the Callback Control Protocol (CBCP) used by Microsoft clients. To disable debugging output, use the no form of this command.

[no] debug ppp cbcp

Syntax Description

cbcp

Causes the debug ppp command to display protocol errors and statistics associated with PPP connection negotiations using MSCB.

Usage Guidelines

Use this command to debug PPP connections on point-to-point links using MS Callback.

The debug ppp command currently exists; only the cbcp keyword is added to support MSCB.

Refer to the Cisco IOS Release 11.3 Debug Command Reference for other keywords available with the debug ppp command.

Sample Display

Figure 1 shows sample debug ppp output using the cbcp keyword. This output depicts packet exchanges under normal PPP operation where the Cisco access server is waiting for the remote PC to respond to the MSCB request. The router also has debug ppp negotiation and service timestamps msec commands enabled.

Figure 1: Sample Debug PPP CBCP Output

Router# debug ppp cbcp
Dec 17 00:48:11.302: As8 MCB: User mscb Callback Number - Client ANY
Dec 17 00:48:11.306: Async8 PPP: O MCB Request(1) id 1 len 9
Dec 17 00:48:11.310: Async8 MCB: O  1  1  0  9  2  5  0  1  0 
Dec 17 00:48:11.314: As8 MCB: O Request Id 1 Callback Type Client-Num delay 0
Dec 17 00:48:13.342: As8 MCB: Timeout in state WAIT_RESPONSE
Dec 17 00:48:13.346: Async8 PPP: O MCB Request(1) id 2 len 9
Dec 17 00:48:13.346: Async8 MCB: O  1  2  0  9  2  5  0  1  0 
Dec 17 00:48:13.350: As8 MCB: O Request Id 2 Callback Type Client-Num delay 0
Dec 17 00:48:15.370: As8 MCB: Timeout in state WAIT_RESPONSE
Dec 17 00:48:15.374: Async8 PPP: O MCB Request(1) id 3 len 9
Dec 17 00:48:15.374: Async8 MCB: O  1  3  0  9  2  5  0  1  0 
Dec 17 00:48:15.378: As8 MCB: O Request Id 3 Callback Type Client-Num delay 0
Dec 17 00:48:17.398: As8 MCB: Timeout in state WAIT_RESPONSE
Dec 17 00:48:17.402: Async8 PPP: O MCB Request(1) id 4 len 9
Dec 17 00:48:17.406: Async8 MCB: O  1  4  0  9  2  5  0  1  0 
Dec 17 00:48:17.406: As8 MCB: O Request Id 4 Callback Type Client-Num delay 0
Dec 17 00:48:19.426: As8 MCB: Timeout in state WAIT_RESPONSE
Dec 17 00:48:19.430: Async8 PPP: O MCB Request(1) id 5 len 9
Dec 17 00:48:19.430: Async8 MCB: O  1  5  0  9  2  5  0  1  0 
Dec 17 00:48:19.434: As8 MCB: O Request Id 5 Callback Type Client-Num delay 0
Dec 17 00:48:21.454: As8 MCB: Timeout in state WAIT_RESPONSE
Dec 17 00:48:21.458: Async8 PPP: O MCB Request(1) id 6 len 9
Dec 17 00:48:21.462: Async8 MCB: O  1  6  0  9  2  5  0  1  0 
Dec 17 00:48:21.462: As8 MCB: O Request Id 6 Callback Type Client-Num delay 0
Dec 17 00:48:23.482: As8 MCB: Timeout in state WAIT_RESPONSE
Dec 17 00:48:23.486: Async8 PPP: O MCB Request(1) id 7 len 9
Dec 17 00:48:23.490: Async8 MCB: O  1  7  0  9  2  5  0  1  0 
Dec 17 00:48:23.490: As8 MCB: O Request Id 7 Callback Type Client-Num delay 0
Dec 17 00:48:25.510: As8 MCB: Timeout in state WAIT_RESPONSE
Dec 17 00:48:25.514: Async8 PPP: O MCB Request(1) id 8 len 9
Dec 17 00:48:25.514: Async8 MCB: O  1  8  0  9  2  5  0  1  0 
Dec 17 00:48:25.518: As8 MCB: O Request Id 8 Callback Type Client-Num delay 0
Dec 17 00:48:26.242: As8 PPP: I pkt type 0xC029, datagramsize 18
Dec 17 00:48:26.246: Async8 PPP: I MCB Response(2) id 8 len 16
Dec 17 00:48:26.250: Async8 MCB: I  2  8  0  10  2  C  C  1  32  34  39  32  36  31  33  0 
Dec 17 00:48:26.254: As8 MCB: Received response
Dec 17 00:48:26.258: As8 MCB: Response CBK-Client-Num 2 12 12,  addr 1-2492613
Dec 17 00:48:26.262: Async8 PPP: O MCB Ack(3) id 9 len 16
Dec 17 00:48:26.266: Async8 MCB: O  3  9  0  10  2  C  C  1  32  34  39  32  36  31  33  0 
Dec 17 00:48:26.270: As8 MCB: O Ack Id 9 Callback Type Client-Num delay 12
Dec 17 00:48:26.270: As8 MCB: Negotiated MCB with peer
Dec 17 00:48:26.390: As8 LCP: I TERMREQ [Open] id 4 len 8 (0x00000000)
Dec 17 00:48:26.390: As8 LCP: O TERMACK [Open] id 4 len 4
Dec 17 00:48:26.394: As8 MCB: Peer terminating the link
Dec 17 00:48:26.402: As8 MCB: Initiate Callback for mscb at 2492613 using Async

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