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
Optimized PPP Negotiation
Feature History
Release
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Modification
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12.2(4)T
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This feature was introduced.
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12.2(11)T
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This feature was implemented on Cisco access server platforms.
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This document describes the Asynchronous Line Monitoring feature 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 Asynchronous Line Monitoring feature 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 Asynchronous Line Monitoring feature 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 Asynchronous Line Monitoring feature 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
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Purpose
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Router(config-if)# ppp lcp predictive
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Sets LCP to a predictive state that reduces negotiation time by predicting responses from peers and sending expected reply and request packets in advance.
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Router(config-if)# ppp ipcp predictive
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Sets IPCP to a predictive state that reduces negotiation time by predicting responses from peers and sending expected reply and request packets in advance.
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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
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Purpose
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Router# show interfaces serial
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Displays information about a serial interface.
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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:
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
clock source line primary
ip address 2.2.2.2 255.255.255.0
isdn switch-type primary-5ess
isdn incoming-voice modem
no peer default ip address
dialer idle-timeout 120000
peer default ip address pool LOCAL
ip local pool LOCAL 2.2.2.10 2.2.2.20
dialer-list 1 protocol ip permit
modem autoconfigure discovery
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:
no peer default ip address
All other commands listed in the "Configuration with a Wireless Dialup Client Example" remain unchanged.
Command Reference
The following commands are introduced or modified in the feature or features documented in this module. For information about these commands, see the Cisco IOS Dial Technologies Command Reference at http://www.cisco.com/en/US/docs/ios/dial/command/reference/dia_book.html. For information about all Cisco IOS commands, go to the Command Lookup Tool at http://tools.cisco.com/Support/CLILookup or to the Cisco IOS Master Commands List.
•ppp lcp predictive
•ppp ipcp predictive
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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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