Table Of Contents

Configuring BACP

BACP Overview

BACP Configuration Options

How to Configure BACP

Enabling BACP

Modifying BACP Passive Mode Default Settings

Configuring Active Mode BACP

Monitoring and Maintaining Interfaces Configured for BACP

Troubleshooting BACP

Configuration Examples for BACP

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 BACP

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

•BACP Overview

•How to Configure BACP

•Monitoring and Maintaining Interfaces Configured for BACP

•Troubleshooting BACP

•Configuration Examples for BACP

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 Bandwidth Allocation Protocol (BAP) call or callback request message, and the removal of a link can be controlled by a link drop message.

To identify the hardware platform or software image information associated with a feature, use the Feature Navigator on Cisco.com to search for information about the feature or refer to the software release notes for a specific release. For more information, see the "Identifying Supported Platforms" section in the "Using Cisco IOS Software" chapter.

For a complete description of the PPP BACP commands in this chapter, refer to the Cisco IOS Dial Technologies Command Reference, Release 12.2. To locate documentation of other commands that appear in this chapter, use the command reference master index or search online.

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 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.

BACP 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—The system initiates outbound calls, sets the parameters for outbound calls, and determines whether links should be added to or removed from a multilink bundle. The system also monitors the multilink load by default.

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.)

A virtual or dialer interface must be configured either to make call requests or to make callback requests, but it cannot be configured to do both.

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 routing (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.

How to Configure BACP

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.

During negotiations with a peer, PPP BACP might respond with a telephone number delta, indicating that the peer should modify certain digits of the dialed phone number and dial again to reach the PPP BACP interface or to set up another link.

BACP can be configured on a virtual template interface or on a dialer interface (including dialer rotary groups and ISDN interfaces).

To configure BACP on a selected interface or interface template, perform the following tasks in the order listed:

•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)

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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.

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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. For details, see the "Troubleshooting BACP" and "Monitoring and Maintaining Interfaces Configured for BACP" sections later in this chapter.

See the section "Configuration Examples for BACP" 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:

Command	Purpose
Router(config-if)# ppp multilink bap or Router(config-if)# ppp multilink bap required	Enables PPP BACP bandwidth allocation negotiation. Enables PPP BACP bandwidth allocation negotiation and enforces mandatory negotiation of BACP for the multilink bundle.

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

•Allows a peer to initiate link addition.

•Allows a peer to initiate link removal.

•Requests that a peer initiate link addition.

•Waits 20 seconds before timing out on pending actions.

•Waits 3 seconds before timing out on not receiving a response from a peer.

•Makes only one attempt to call a number.

•Makes up to three retries for sending a request.

•Searches for and logs up to five free dialers.

•Makes three attempts to send a call status indication.

•Adds only ISDN links to a multilink bundle.

•Monitors load.

The default settings will be in effect in the environment for which the ppp multilink bap command is entered:

•Virtual template interface, if that is where the command is entered.

When the command is entered in a virtual template interface, configuration applies to any virtual access interface that is created dynamically under Multilink PPP, the application that defines the template.

•Dialer interface, if that is where the command is entered.

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:

Command	Purpose
Router(config-if)# ppp bap timeout pending seconds	Modifies the timeout on pending actions.
Router(config-if)# ppp bap timeout response seconds	Modifies the timeout on not receiving a response from a peer.
Router(config-if)# ppp bap max dial-attempts number	Modifies the number of attempts to call a number.
Router(config-if)# ppp bap max ind-retries number	Modifies the number of times to send a call status indication.
Router(config-if)# ppp bap max req-retries number	Modifies the number of retries of a particular request.
Router(config-if)# ppp bap max dialers number	Modifies the maximum number of free dialers logged.
Router(config-if)# ppp bap link types analog or Router(config-if)# ppp bap link types isdn analog	Specifies that only analog links can be added to a multilink bundle. Allows both ISDN and analog links to be added.
Router(config-if)# ppp bap number default phone-number	For all DDR-capable interfaces in the group, specifies a primary telephone number for the peer to call for PPP BACP negotiation, if different from any base number defined on the dialer interface or virtual template interface.
Router(config-if)# ppp bap number secondary phone-number	For BRI interfaces on which a different number is provided for each B channel, specifies the secondary telephone number.
Router(config-if)# ppp bap drop timer seconds	Specifies a time to wait between outgoing link drop requests.
Router(config-if)# no ppp bap monitor load	Disables the default monitoring of load and the validation of peer requests against load thresholds.

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.

Command	Purpose
Router(config-if)# ppp bap call request	Enables the interface to initiate the addition of links to the multilink bundle.
Router(config-if)# ppp bap callback accept	Enables the interface to initiate the addition of links upon peer request.
Router(config-if)# ppp bap drop after-retries	Enables the interface to drop a link without negotiation after receiving no response to retries to send a drop request.
Router(config-if)# ppp bap call timer seconds	Sets the time to wait between outgoing call requests.
Router(config-if)# ppp bap timeout pending seconds	Modifies the timeout on pending actions.
Router(config-if)# ppp bap timeout response seconds	Modifies the timeout on not receiving a response from a peer.
Router(config-if)# ppp bap max dial-attempts number	Modifies the number of attempts to call a number.
Router(config-if)# ppp bap max ind-retries number	Modifies the number of times to send a call status indication.
Router(config-if)# ppp bap max req-retries number	Modifies the number of retries of a particular request.
Router(config-if)# ppp bap max dialers number	Modifies the maximum number of free dialers logged.
Router(config-if)# ppp bap link types analog or Router(config-if)# ppp bap link types isdn analog	Specifies that only analog links can be added to a multilink bundle. Allows both ISDN and analog links to be added.
Router(config-if)# ppp bap number default phone-number	For all DDR-capable interfaces in the group, specifies a primary telephone number for the peer to call for PPP BACP negotiation, if different from any base number defined on the dialer interface or virtual template interface.
Router(config-if)# ppp bap number secondary phone-number	For BRI interfaces on which a different number is provided for each B channel, specifies the secondary telephone number.

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
Router> show ppp bap group [name]	Displays information about all PPP BACP multilink bundle groups or a specific, named multilink bundle group.
Router> show ppp bap queues	Displays information about the BACP queues.
Router> show ppp multilink	Displays information about the dialer interface, the multilink bundle, and the group members.
Router> show dialer	Displays BACP numbers dialed and the reasons for the calls.
Router> 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
Router> debug ppp bap [error | event | negotiation]	Displays BACP errors, protocol actions, and negotiation events and transitions.
Router> debug ppp multilink events	Displays information about events affecting multilink bundles established for BACP.

Configuration Examples for BACP

The following sections provide 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

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.

The following example creates a bundle on a BRI 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

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Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers. Any examples, command display output, network topology diagrams, and other figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses or phone numbers in illustrative content is unintentional and coincidental.

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