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Cisco IOS Software Releases 12.2 T

Optimized PPP Negotiation

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Table Of Contents

Optimized PPP Negotiation

Feature Overview

Benefits

Related Documents

Supported Platforms

Supported Standards, MIBs, and RFCs

Configuration Tasks

Configuring the LCP and IPCP Predictive States

Verifying LCP and IPCP Predictive States

Troubleshooting Tips

Monitoring and Maintaining LCP and IPCP Predictive States

Configuration Examples

Configuration with a Wireless Dialup Client Example

Dialup Connection with Router as Client Example

Command Reference

ppp lcp predictive

ppp ipcp predictive


Optimized PPP Negotiation

Feature History

Release
Modification

12.2(4)T

This feature was introduced.

12.2(11)T

This feature was implemented on Cisco access server platforms.


This document describes the Optimized PPP Negotiation feature. It includes the following sections:

•Feature Overview

•Supported Platforms

•Supported Standards, MIBs, and RFCs

•Configuration Tasks

•Monitoring and Maintaining LCP and IPCP Predictive States

•Configuration Examples

•Command Reference

Feature Overview

The Optimized PPP Negotiation feature optimizes the time needed for PPP negotiation when a connection is made. PPP negotiation can include several cycles before the negotiation options are acknowledged. These negotiation cycles can cause a significant user-perceived delay, especially in networks with slow links such as a wireless data connection, where the round-trip time for the negotiation cycle can take 600 to 800 ms or more. Additionally, the PPP negotiation time can add significantly to the total time the user stays connected in these types of connections. The following changes to the PPP link control protocol (LCP) and PPP Internet Protocol Control Protocol (IPCP) negotiation strategies make a reduction in the negotiation time possible:

•Send an LCP Configure-Ack packet, then send the next-level LCP Configure-Request packet before receiving acknowledgment for the PPP Configure-Request packet.

•Send an LCP Configure-Ack packet after sending LCP Configure-Reject and Configure-Nak packets for certain configuration options.

•Send an IPCP Configure-Ack packet after sending an IPCP Configure-Nak packet.

•Send IPCP Configure-Nak and Configure-Ack packets after rejecting certain configuration options.

Benefits

The Optimized PPP Negotiation feature reduces delay in PPP negotiation time by predicting responses from peers and sending expected reply and request packets in advance, yet allows PPP negotiations to remain compliant with RFC 1661, the industry standard for transporting multiprotocol datagrams over point-to-point links.

Related Documents

Refer to the part "PPP Configuration" in the Cisco IOS Dial Technologies Configuration Guide,
Release 12.2, for more information about configuring PPP.

Supported Platforms

See the next section for information about Feature Navigator and how to use this tool to determine the platforms and software images in which this feature is available.

Determining Platform Support Through Feature Navigator

Cisco IOS software is packaged in feature sets that support specific platforms. To get updated information regarding platform support for this feature, access Feature Navigator. Feature Navigator dynamically updates the list of supported platforms as new platform support is added for the feature.

Feature Navigator is a web-based tool that enables you to quickly determine which Cisco IOS software images support a specific set of features and which features are supported in a specific Cisco IOS image.

To access Feature Navigator, you must have an account on Cisco.com. If you have forgotten or lost your account information, send a blank e-mail to cco-locksmith@cisco.com. An automatic check will verify that your e-mail address is registered with Cisco.com. If the check is successful, account details with a new random password will be e-mailed to you. Qualified users can establish an account on Cisco.com by following the directions at http://www.cisco.com/register.

Feature Navigator is updated regularly when major Cisco IOS software releases and technology releases occur. For the most current information, go to the Feature Navigator home page at the following URL:

http://www.cisco.com/go/fn

Supported Standards, MIBs, and RFCs

Standards

None

MIBs

None

To obtain lists of supported MIBs by platform and Cisco IOS release, and to download MIB modules, go to the Cisco MIB website on Cisco.com at the following URL:

http://www.cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml

RFCs

•RFC 1661, The Point-to-Point Protocol

Configuration Tasks

See the following sections for configuration tasks for the Optimized PPP Negotiation feature. Each task in the list is identified as either required or optional:

•Configuring the LCP and IPCP Predictive States (required)

•Verifying LCP and IPCP Predictive States (required)

Configuring the LCP and IPCP Predictive States

The ppp lcp predictive and ppp ipcp predictive commands are configured on group asynchronous and dialer rotary group interfaces in a dialup network that uses PPP or Multilink PPP. Begin configuration in global configuration mode and use the interface group-async and interface dialer commands to start interface configuration mode.

To configure the LCP and IPCP predictive states, use the following commands in interface configuration mode, as needed:

Command
Purpose

Router(config-if)# ppp lcp predictive

Sets LCP to a predictive state that reduces negotiation time by predicting responses from peers and sending expected reply and request packets in advance.

Router(config-if)# ppp ipcp predictive

Sets IPCP to a predictive state that reduces negotiation time by predicting responses from peers and sending expected reply and request packets in advance.

See the section "Configuration Examples" for examples of how to configure a network that would make use of the ppp lcp predictive and ppp ipcp predictive commands.

Verifying LCP and IPCP Predictive States

To verify that the LCP and IPCP predictive states are configured correctly, use the debug ppp negotiation command in privileged EXEC mode.

In the following sample output, lines in bold text indicate reports of LCP and IPCP negotiations in the predictive state configured by the ppp lcp predictive and ppp ipcp predictive commands: 

Router# debug ppp negotiation


*Mar  2 02:25:27.693: %LINK-3-UPDOWN: Interface Serial0/0, changed state to up

*Mar  2 02:25:27.693: Se0/0 PPP: Treating connection as a dedicated line

*Mar  2 02:25:27.693: Se0/0 PPP: Phase is ESTABLISHING, Active Open

*Mar  2 02:25:27.693: Se0/0 LCP: O CONFREQ [Closed] id 11 len 10

*Mar  2 02:25:27.693: Se0/0 LCP:    MagicNumber 0x35C4DB07 (0x050635C4DB07)

*Mar  2 02:25:27.729: Se0/0 LCP: I CONFREQ [REQsent] id 14 len 29

*Mar  2 02:25:27.729: Se0/0 LCP:    MagicNumber 0xBFAE7481 (0x0506BFAE7481)

*Mar  2 02:25:27.729: Se0/0 LCP:    MRRU 1524 (0x110405F4)

*Mar  2 02:25:27.729: Se0/0 LCP:    EndpointDisc 1 Local (0x130F01696F7377616ED3 23630 3063)

*Mar  2 02:25:27.729: Se0/0 LCP: O CONFREJ [REQsent] id 14 len 23

*Mar  2 02:25:27.729: Se0/0 LCP:    MRRU 1524 (0x110405F4)

*Mar  2 02:25:27.733: Se0/0 LCP:    EndpointDisc 1 Local (0x130F01696F7377616ED3 23630 3063)

*Mar  2 02:25:27.733: Se0/0 LCP: O CONFACK [REQsent] id 15 len 10

*Mar  2 02:25:27.733: Se0/0 LCP:    MagicNumber 0xBFAE7481 (0x0506BFAE7481)

*Mar  2 02:25:27.733: Se0/0 LCP: State is Open

*Mar  2 02:25:27.733: Se0/0 PPP: Phase is UP

*Mar  2 02:25:27.737: Se0/0 IPCP: O CONFREQ [Closed] id 10 len 16

*Mar  2 02:25:27.737: Se0/0 IPCP:    CompressType VJ 15 slots (0x0206002D0F00)

*Mar  2 02:25:27.737: Se0/0 IPCP:    Address 10.1.30.200 (0x03060A011EC8)

*Mar  2 02:25:27.745: Se0/0 LCP: I CONFACK [Open] id 11 len 10

*Mar  2 02:25:27.745: Se0/0 LCP:    MagicNumber 0x35C4DB07 (0x050635C4DB07)

*Mar  2 02:25:27.777: Se0/0 LCP: I CONFREQ [Open] id 15 len 10

*Mar  2 02:25:27.781: Se0/0 LCP:    MagicNumber 0xBFAE7481 (0x0506BFAE7481)

*Mar  2 02:25:27.781: Se0/0 LCP: Dropping packet, state is Open

*Mar  2 02:25:27.813: Se0/0 IPCP: I CONFREQ [REQsent] id 105 len 28

*Mar  2 02:25:27.813: Se0/0 IPCP:    CompressType VJ 15 slots (0x0206002D0F00)

*Mar  2 02:25:27.813: Se0/0 IPCP:    Address 0.0.0.0 (0x030600000000)

*Mar  2 02:25:27.813: Se0/0 IPCP:    PrimaryDNS 0.0.0.0 (0x810600000000)

*Mar  2 02:25:27.813: Se0/0 IPCP:    SecondaryDNS 0.0.0.0 (0x830600000000)

*Mar  2 02:25:27.813: Se0/0 IPCP: Pool returned 10.1.30.109

*Mar  2 02:25:27.817: Se0/0 IPCP: O CONFREJ [REQsent] id 105 len 16

*Mar  2 02:25:27.817: Se0/0 IPCP:    PrimaryDNS 0.0.0.0 (0x810600000000)

*Mar  2 02:25:27.817: Se0/0 IPCP:    SecondaryDNS 0.0.0.0 (0x830600000000)

*Mar  2 02:25:27.817: Se0/0 IPCP: O CONFNAK [REQsent] id 106 len 10

*Mar  2 02:25:27.817: Se0/0 IPCP:    Address 10.1.30.109 (0x03060A011E6D)

*Mar  2 02:25:27.817: Se0/0 IPCP: O CONFACK [REQsent] id 107 len 16

*Mar  2 02:25:27.817: Se0/0 IPCP:    CompressType VJ 15 slots (0x0206002D0F00)

*Mar  2 02:25:27.821: Se0/0 IPCP:    Address 10.1.30.109 (0x03060A011E6D)

*Mar  2 02:25:27.833: Se0/0 IPCP: I CONFACK [ACKsent] id 10 len 16

*Mar  2 02:25:27.833: Se0/0 IPCP:    CompressType VJ 15 slots (0x0206002D0F00)

*Mar  2 02:25:27.833: Se0/0 IPCP:    Address 10.1.30.200 (0x03060A011EC8)

*Mar  2 02:25:27.833: Se0/0 IPCP: State is Open

*Mar  2 02:25:27.837: Se0/0 IPCP: Install route to 10.1.30.109

*Mar  2 02:25:27.837: Se0/0 IPCP: Add link info for cef entry 10.1.30.109

*Mar  2 02:25:27.861: Se0/0 IPCP: I CONFREQ [Open] id 106 len 16

*Mar  2 02:25:27.865: Se0/0 IPCP:    CompressType VJ 15 slots (0x0206002D0F00)

*Mar  2 02:25:27.865: Se0/0 IPCP:    Address 0.0.0.0 (0x030600000000)

*Mar  2 02:25:27.865: Se0/0 IPCP: Dropping packet, state is Open

*Mar  2 02:25:27.881: Se0/0 IPCP: I CONFREQ [Open] id 107 len 16

*Mar  2 02:25:27.885: Se0/0 IPCP:    CompressType VJ 15 slots (0x0206002D0F00)

*Mar  2 02:25:27.885: Se0/0 IPCP:    Address 10.1.30.109 (0x03060A011E6D)

*Mar  2 02:25:27.885: Se0/0 IPCP: Dropping packet, state is Open

*Mar  2 02:25:28.733: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0/, changed 
state to up

Refer to RFC 1661 for more information about the PPP link operation. To turn off debug messaging, enter the undebug ppp negotiation command in privileged EXEC mode.

Troubleshooting Tips

See the section "Verifying LCP and IPCP Predictive States" to troubleshoot the LCP and IPCP predictive states.

Monitoring and Maintaining LCP and IPCP Predictive States

To monitor and maintain interfaces using LCP and IPCP predictive states, use the following command in EXEC mode:

Command
Purpose

Router# show interfaces serial

Displays information about a serial interface.


Configuration Examples

This section provides the following configuration examples:

•Configuration with a Wireless Dialup Client Example

•Dialup Connection with Router as Client Example

Configuration with a Wireless Dialup Client Example

The following configuration supports a PC running Windows 95 or Windows NT, and a dialup client such as a cell phone: 

hostname s5300

!

isdn switch-type primary-5ess

!

chat-script usr2 ABORT ERROR ABORT BUSY "" "ATZ" OK "ATDT \T" TIMEOUT 30 CONNECT

chat-script usr ABORT ERROR ABORT BUSY "" "ATZ" OK "ATDT \T" TIMEOUT 30  CONNECTfax 
interface-type modem

!

controller t1 0

 framing esf

 clock source line primary

 linecode b8zs

 pri-group timeslots 1-24

!

interface loopback 0

 ip address 2.2.2.2 255.255.255.0

 no ip mroute-cache

!

interface serial 0:23

 no ip address

 encapsulation ppp

 no keepalive

 dialer pool-member 1

 isdn switch-type primary-5ess

 isdn incoming-voice modem

 no peer default ip address

 no fair-queue

 no cdp enable

!

interface group-async1

 ip unnumbered loopback 0

 encapsulation ppp

 no ip mroute-cache

 dialer in-band

 dialer pool-member 1

 async dynamic address

 async dynamic routing

 async mode dedicated

 no fair-queue

 ppp lcp predictive

 ppp ipcp predictive

 group-range 1 48

 hold-queue 75 in

!

interface dialer 1

 ip unnumbered loopback 0

 encapsulation ppp

 dialer pool 1

 dialer idle-timeout 120000

 dialer enable-timeout 6

 dialer-group 1

 peer default ip address pool LOCAL

 no cdp enable

 ppp lcp predictive

 ppp ipcp predictive

 ppp multilink

!

ip local pool LOCAL 2.2.2.10 2.2.2.20

!

dialer-list 1 protocol ip permit

no cdp run

!

line con 0

 exec-timeout 0 0

 transport input none

line 1 48

 script dialer usr

 login

 modem InOut

 modem autoconfigure discovery

 transport preferred none

 transport input all

 transport output none

 autoselect during-login

 autoselect ppp

line aux 0

line vty 0 4

 password lab

 login

!

end

Dialup Connection with Router as Client Example

To change the configuration in the previous example so that the network supports the router rather than a PC device as the dialup client, change the dialer interface portion of the configuration commands (the portion beginning with the interface dialer 1 command) as follows: 

!

interface dialer 1

no peer default ip address

end

All other commands listed in the "Configuration with a Wireless Dialup Client Example" remain unchanged.

Command Reference

This section documents new commands. All other commands used with this feature are documented in the Cisco IOS Release 12.2 command reference publications.

•ppp lcp predictive

•ppp ipcp predictive

ppp lcp predictive

To set the PPP link control protocol (LCP) to a predictive state that reduces negotiation time by predicting responses from peers and sending expected reply and request packets in advance, use the ppp lcp predictive command in interface configuration mode. To disable the LCP predictive state, use the no form of this command.

ppp lcp predictive

no ppp lcp predictive

Syntax Description

This command has no arguments or keywords.

Defaults

Disabled

Command Modes

Interface configuration

Command History

Release
Modification

12.2(4)T

This command was introduced.

12.2(11)T

This feature was implemented on Cisco access server platforms.


Usage Guidelines

The ppp lcp predictive command is useful in networks that accept connections from devices that require a reduction in the LCP negotiation cycle time. This command reduces the amount of time needed for PPP to negotiate with the peer so that connections can be made in an acceptable amount of time. The following changes to the LCP negotiation strategy make this time reduction possible:

•Send an LCP Configure-Ack packet, then send the next-level LCP Configure-Request packet before receiving acknowledgment for the PPP Configure-Request packet.

•Send an LCP Configure-Ack packet after sending LCP Configure-Reject and Configure-Nak packets for certain configuration options.

These changes can reduce connection delay by approximately 40 percent.

The ppp lcp predictive command is configured on group asynchronous and dialer interfaces running PPP or Multilink PPP.

Examples

The following example sets LCP and IPCP to predictive states on a dialer interface: 

!

interface dialer 1

 ip unnumbered loopback 0

 encapsulation ppp

 dialer pool 1

 dialer idle-timeout 120000

 dialer enable-timeout 6

 dialer-group 1

 peer default ip address pool LOCAL

 no cdp enable

 ppp lcp predictive

 ppp ipcp predictive

 ppp multilink

Related Commands

Command
Description

interface dialer

Defines a dialer rotary group.

interface group-async

Creates a group interface that will serve as master, to which asynchronous interfaces can be associated as members.

ppp ipcp predictive

Sets IPCP to a predictive state that reduces negotiation time by predicting responses from peers and sending expected reply and request packets in advance.


ppp ipcp predictive

To set the PPP Internet Protocol Control Protocol (IPCP) to a predictive state that reduces negotiation time by predicting responses from peers and sending expected reply and request packets in advance, use the ppp ipcp predictive command in interface configuration mode. To disable the IPCP predictive state, use the no form of this command.

ppp ipcp predictive

no ppp ipcp predictive

Syntax Description

This command has no arguments or keywords.

Defaults

Disabled

Command Modes

Interface configuration

Command History

Release
Modification

12.2(4)T

This command was introduced.

12.2(11)T

This feature was implemented on Cisco access server platforms.


Usage Guidelines

The ppp ipcp predictive command is useful in networks that accept connections from devices that require a reduction in the IPCP negotiation cycle time. This command reduces the amount of time needed for PPP to negotiate with the peer so that connections can be made in an acceptable amount of time. The following changes to the IPCP negotiation strategy make this time reduction possible:

•Send an IPCP Configure-Ack packet after sending an IPCP Configure-Nak packet.

•Send IPCP Configure-Nak and Configure-Ack packets after rejecting certain configuration options.

These changes can reduce connection delay by approximately 40 percent.

Note Any Configure-Request packet received in the Open state is ignored until the software receives Configure-Request packets with identifying numbers greater than what was last acknowledged, in which case the software disables the predictive mode and processes the Configure-Request packet using normal IPCP negotiation operations.

The ppp ipcp predictive command is configured on group asynchronous and dialer interfaces running PPP or Multilink PPP.

Examples

The following example sets LCP and IPCP to predictive states on a group asynchronous interface: 

interface group-async 1

 ip unnumbered loopback 0

 encapsulation ppp

 no ip mroute-cache

 dialer in-band

 dialer pool-member 1

 async dynamic address

 async dynamic routing

 async mode dedicated

 no fair-queue

 ppp lcp predictive

 ppp ipcp predictive

 group-range 1 48

 hold-queue 75 in

Related Commands

Command
Description

interface dialer

Defines a dialer rotary group.

interface group-async

Creates a group interface that will serve as master, to which asynchronous interfaces can be associated as members.

ppp lcp predictive

Sets LCP to a predictive state that reduces negotiation time by predicting responses from peers and sending expected reply and request packets in advance.