Table of Contents

BACP Overview

Configuration Options

BACP Configuration Task List

Enabling BACP
Modifying BACP Passive Mode Default Settings
Configuring Active Mode BACP

Monitoring and Maintaining Interfaces Configured for BACP
Troubleshooting BACP
BACP Configuration Examples

Basic BACP Configurations
Dialer Rotary Group with Different Dial-In Numbers
Passive Mode Dialer Rotary Group Members with One Dial-In Number
PRI Interface with No Defined PPP BACP Number
BRI Interface with No Defined BACP Number

Configuring the Bandwidth
Allocation Control Protocol

This chapter describes how to configure the Bandwidth Allocation Control Protocol (BACP), described in RFC 2125. It includes the following main sections:

• BACP Overview

• BACP Configuration Task List

• Monitoring and Maintaining Interfaces Configured for BACP

• Troubleshooting BACP

• BACP Configuration Examples

BACP requires a system only to have the knowledge of its own phone numbers and link types. A system must be able to provide the phone numbers and link type to its peer to satisfy the call control mechanism. (Certain situations might not be able to satisfy this requirement; numbers might not be present because of security considerations.)

BACP is designed to operate in both the virtual interface environment and the dialer interface environment. It can operate over any physical interface that is Multilink PPP-capable and has a dial capability; at initial release, BACP supports ISDN and asynchronous serial interfaces.

The addition of any link to an existing multilink bundle is controlled by a BAP call or callback request message, and the removal of a link can be controlled by a link drop message.

BACP Overview

The BACP provides Multilink PPP (MLP) peers with the ability to govern link utilization. Once peers have successfully negotiated BACP, they can use the Bandwidth Allocation Protocol (BAP), which is a subset of BACP, to negotiate bandwidth allocation. BAP provides a set of rules governing dynamic bandwidth allocation through call control; a defined method for adding and removing links from a multilink bundle for Multilink PPP is used.

BACP provides the following benefits:

• Allows multilink implementations to interoperate by providing call control through the use of link types, speeds, and telephone numbers.

• Controls thrashing caused by links being brought up and removed in a short period of time.

• Ensures that both ends of the link are informed when links are added or removed from a multilink bundle.

For simplicity, the remaining text of this chapter makes no distinction between BACP and BAP; only BACP is mentioned.

Configuration Options

PPP BACP can be configured to operate in the following ways:

• Passive mode (default)---The system accepts incoming calls; the calls might request callback, addition of a link, or removal of a link from a multilink bundle. The system also monitors the multilink load by default.

Passive mode is for virtual template interfaces or for dialer interfaces.

Active mode is for dialer interfaces, but not for virtual template interfaces. (If you attempt to configure active mode on a virtual template interface, no calls will be made.)

Support of BACP on virtual interfaces in an Multichassis Multilink PPP (MMP) environment is restricted to incoming calls on the multilink group. Support of BACP for outgoing calls is provided by dialer interface configuration only.

BACP supports only ISDN and asynchronous serial interfaces.

Dialer support is provided only for legacy dial-on-demand (DDR) dialer configurations; BACP cannot be used in conjunction with the DDR dialer profiles feature.

BACP is configured on virtual template interfaces and physical interfaces that are multilink capable. For both the virtual template interfaces and the dialer interfaces, BACP requires MMP and bidirectional dialing to be working between the routers that will negotiate control and allocation of bandwidth for the multilink bundle.

BACP Configuration Task List

Before you configure BACP on an interface, determine the following important information. The router might be unable to connect to a peer if this information is incorrect.

• Type of link (ISDN or analog) to be used. Link types must match on the local and remote ends of the link.

• Line speed needed to reach the remote peer. The speed configured for the local physical interface must be at least that of the link. The bandwidth command or the dialer map command with the speed keyword can be used.

• Local telephone number to be used for incoming PPP BACP calls, if it is different from a rotary group base number or if incoming PPP BACP calls should be directed to a specific number.

• Enabling BACP (Required)

Passive mode is in effect and the values of several parameters are set by default when PPP BACP is enabled. If you can accept all the passive mode parameters, do not continue with the tasks.

• Modifying BACP Passive Mode Default Settings (As Required)

or

• Configuring Active Mode BACP (As Required)

Note You can configure one interface in passive mode and another in active mode so that one interface accepts incoming call requests and makes callback requests (passive mode), and the other interface makes call requests and accepts callback requests (active mode). A dialer or virtual template interface should be configured to reflect the required dial capability of the interface. A dial-in pool (in passive mode) might have no requirement to dial out but might want remote users to add multiple links, with the remote user incurring the cost of the call. Similarly, a dial-out configuration (active mode) suggests that the router is a client, rather than a server, on that link. The active-mode user incurs the cost of additional links.

You might need to configure a base telephone number, if it is applicable to your dial-in environment. This number is one that remote users can dial to establish a connection. Otherwise, individual PPP BACP links might need numbers. Information is provided in the task lists for configuring passive mode or active mode PPP BACP. See the ppp bap number command options in the task lists.

You can also troubleshoot BACP configuration and operations and monitor interfaces configured for PPP BACP. See the "Troubleshooting BACP" and "Monitoring and Maintaining Interfaces Configured for BACP" sections for later in this chapter for details.

See the section "BACP Configuration Examples" at the end of this chapter for examples of PPP BACP configuration.

Enabling BACP

To enable PPP bandwidth allocation control and dynamic allocation of bandwidth, use one of the following commands in interface configuration mode:

When PPP BACP is enabled, it is in passive mode by default and the following settings are in effect:

See the section "Basic BACP Configurations" at the end of this chapter for an example of how to configure BACP.

Modifying BACP Passive Mode Default Settings

To modify the default parameter values or to configure additional parameters in passive mode, use the following commands, as needed, in interface configuration mode for the interface or virtual template interface that is configured for PPP BACP:

See the section "Passive Mode Dialer Rotary Group Members with One Dial-In Number" later in this chapter for an example of how to configure passive mode parameters.

Configuring Active Mode BACP

To configure active mode BACP, use the following commands in interface configuration mode for the dialer interface on which BACP was enabled. For your convenience, the commands that make BACP function in active mode are presented before the commands that change default parameters or add parameters.

When BACP is enabled, multiple dialer maps to one destination are not needed when they differ only by number. That is, once the initial call has been made to create the bundle, further dialing attempts are realized through the BACP phone number negotiation.

Outgoing calls are supported through the use of dialer maps. However, when an initial incoming call creates a dynamic dialer map, the router can dial out if the peer supplies a phone number. This capability is achieved by the dynamic creation of static dialer maps for BACP. These temporary dialer maps can be displayed by using the show dialer map command. These temporary dialer maps last only as long as the BACP group lasts and are removed when the BACP group or the associated map is removed.

Monitoring and Maintaining Interfaces Configured for BACP

To monitor interfaces configured for PPP BACP, use any of the following commands in EXEC mode:

Command	Purpose
show ppp bap group [name]	Displays information about all PPP BACP multilink bundle groups or a specific, named multilink bundle group.
show ppp bap queues	Displays information about the BACP queues.
show ppp multilink	Displays information about the dialer interface, the multilink bundle, and the group members.
show dialer	Displays BACP numbers dialed and the reasons for the calls.
show dialer map	Displays configured dynamic and static dialer maps and dynamically created BACP temporary static dialer maps.

Troubleshooting BACP

To troubleshoot the BACP configuration and operation, use the following debug commands:

Command	Purpose
debug ppp bap [error | event | negotiation]	Displays BACP errors, protocol actions, and negotiation events and transitions.
debug ppp multilink events	Displays information about events affecting multilink bundles established for BACP.

BACP Configuration Examples

This section provides the following configuration examples:

• Basic BACP Configurations

• Dialer Rotary Group with Different Dial-In Numbers

• Passive Mode Dialer Rotary Group Members with One Dial-In Number

• PRI Interface with No Defined PPP BACP Number

• BRI Interface with No Defined BACP Number

Basic BACP Configurations

The following example configures an ISDN BRI interface for BACP to make outgoing calls and prevent the peer from negotiating link drops:

interface bri 0
 ip unnumbered ethernet 0
 dialer load-threshold 10 either
 dialer map ip 172.21.13.101 name bap-peer 12345668899
 encapsulation ppp
 ppp multilink bap
 ppp bap call request
 ppp bap callback accept
 no ppp bap call accept
 no ppp bap drop accept
 ppp bap pending timeout 30
 ppp bap number default 5664567
 ppp bap number secondary 5664568
 

The following example configures a dialer rotary group to accept incoming calls:

interface async 1
 no ip address
 encapsulation ppp
 dialer rotary-group 1
 ppp bap number default 5663456
!
! Set the bandwidth to suit the modem/line speed on the remote side.
interface bri 0
 no ip address
 bandwidth 38400
 encapsulation ppp
 dialer rotary-group 1
 ppp bap number default 5663457
!
interface bri 1
 no ip address
 encapsulation ppp
 dialer rotary-group 1
 ppp bap number default 5663458
!
interface dialer1
 ip unnumbered ethernet 0
 encapsulation ppp
 ppp multilink bap
 ppp bap call accept
 ppp bap link types isdn analog
 dialer load threshold 30
 ppp bap timeout pending 60
 

The following example configures a virtual template interface to use BACP in passive mode:

multilink virtual-template 1
!
interface virtual-template 1
 ip unnumbered ethernet 0
 encapsulation ppp
 ppp multilink bap
 ppp authentication chap callin
 

The bundle is created from any MMP-capable interface.

interface bri 0
 no ip address
 encapsulation ppp
 ppp multilink
 ppp bap number default 4000
 ppp bap number secondary 4001

Dialer Rotary Group with Different Dial-In Numbers

The following example configures a dialer rotary group that has four members, each with a different number, and that accepts incoming dial attempts. The dialer interface does not have a base phone number; the interface used to establish the first link in the multilink bundle will provide the appropriate number from its configuration.

interface bri 0
 no ip address
 encapsulation ppp
dialer rotary-group 1
 no fair-queue
 no cdp enable
 ppp bap number default 6666666
!
interface bri 1
 no ip address
 encapsulation ppp
dialer rotary-group 1
 no fair-queue
 no cdp enable
 ppp bap number default 6666667
!
interface bri 2
 no ip address
 encapsulation ppp
dialer rotary-group 1
 no fair-queue
 no cdp enable
 ppp bap number default 6666668
!
interface bri 3
 no ip address
 encapsulation ppp
dialer rotary-group 1
 no fair-queue
 no cdp enable
 ppp bap number default 6666669
!
interface dialer 1
 ip unnumbered Ethernet0
 encapsulation ppp
 dialer in-band
 dialer idle-timeout 300
 dialer-group 1
 no fair-queue
 no cdp enable
 ppp authentication chap
 ppp multilink bap
 ppp bap call accept
 ppp bap callback request
 ppp bap timeout pending 20
 ppp bap timeout response 2
 ppp bap max dial-attempts 2
 ppp bap monitor load

Passive Mode Dialer Rotary Group Members with One Dial-In Number

The following example, a dialer rotary group with two members each with the same number, accepts incoming dial attempts. The dialer interface has a base phone number because each of its member interfaces is in a hunt group and the same number can be used to access each individual interface.

interface bri 0
 no ip address
 encapsulation ppp
dialer rotary-group 1
 no fair-queue
 no cdp enable
!
interface bri 1
 no ip address
 encapsulation ppp
dialer rotary-group 1
 no fair-queue
 no cdp enable
!
interface dialer 1
 ip unnumbered Ethernet0
 encapsulation ppp
 dialer in-band
 dialer idle-timeout 300
 dialer-group 1
 no fair-queue
 no cdp enable
 ppp authentication chap
 ppp multilink bap
 ppp bap call accept
 ppp bap callback request
 ppp bap timeout pending 20
 ppp bap timeout response 2
 ppp bap max dial-attempts 2
 ppp bap monitor load
 ppp bap number default 6666666

PRI Interface with No Defined PPP BACP Number

In the following example, a PRI interface has no BACP number defined and accepts incoming dial attempts (passive mode). The PRI interface has no base phone number defined, so each attempt to add a link would result in a delta of zero being provided to the calling peer. To establish the bundle, the peer should then dial the same number as it originally used.

interface serial 0:23
 ip unnumbered Ethernet0
 encapsulation ppp
 dialer in-band
 dialer idle-timeout 300
 dialer-group 1
 no fair-queue
 no cdp enable
 ppp authentication chap
 ppp multilink bap
 ppp bap call accept
 ppp bap callback request
 ppp bap timeout pending 20
 ppp bap timeout response 2
 ppp bap max dial-attempts 2
 ppp bap monitor load

BRI Interface with No Defined BACP Number

In the following example, the BRI interface has no base phone number defined. The number that it uses to establish the bundle is that from the dialer map, and all phone delta operations are applied to that number.

interface bri 0
 ip unnumbered Ethernet0
 encapsulation ppp
 dialer in-band
 dialer idle-timeout 300
 dialer map ip 10.1.1.1 name bap_peer speed 56 19998884444
 dialer-group 1
 no fair-queue
 no cdp enable
 ppp authentication chap
 ppp multilink bap
 ppp bap call request
 ppp bap timeout pending 20
 ppp bap timeout response 2
 ppp bap max dial-attempts 2
 ppp bap monitor load

Posted: Tue Jul 18 15:16:53 PDT 2000
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