Diagnosing and Troubleshooting Async MPPP

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Updated:January 11, 2001

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Diagnosing and Troubleshooting Async Multilink PPP

Table Of Contents

Diagnosing and Troubleshooting Async Multilink PPP

Async MPPP Troubleshooting Tables


Diagnosing and Troubleshooting Async Multilink PPP

This chapter focuses on diagnosing and troubleshooting typical async multilink PPP problems. This section reviews the case study environment.

2.1 Async MPPP Troubleshooting Tables

The following symptoms are addressed in separate tables in this section:

•Multilink fails

•Calls fail to connect

•Poor performance

•IP connectivity is down

•Phone calls last too long

•Calling too often

•Calling too infrequently

•Intermittent user access

Table 2-1 Multilink fails

Problem
Suggested Diagnostic Steps

Phone lines are not functional.

1. Dial the PSTN number of the central router; listen for modem trainup (squelch).

2. If this is a problem, you will not hear the dial tone or the squelch.

PC: Dialup Networking (DUN) version 1.2b or lower (or DUN not supported by client).

1. Determine if multilink is supported by version of PC DUN (in verification lab tests, a PC running Windows 95 was used).

2. Navigate to the Dial-Up Networking (DUN) folder.

3. Right click on one of the connections and view properties.

4. Verify that the multilink tab appears at the top of the window.

5. If not, upgrade to a more recent version of PC DUN.

PC: Second modem configured incorrectly.

1. Configure the client as discussed in the following document:

•http://www.cisco.com/warp/public/793/access_dial/async_multilink.html#config

2. Ensure the prefixes are entered correctly.

3. Ensure second modem is added.

4. Ensure that target dial number is entered correctly.

5. Ensure that area code is not included for second modem.

6. Also, refer to this document:

•http://www.cisco.com/warp/public/76/modem_tuning.html

Router: Modem failure

1. Reverse telnet to each modem separately.

a. Refer to the following document for notes about reverse telnet:

–http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/12cgcr/dial_c/dcrtelnt.htm

2. Enter the AT command.

3. Look for Ok response.

4. If Ok is not returned, troubleshoot hardware for other problems.

5. For routers with external modems, enter the ATM1 command to enable the modem's speaker.

6. Enter the ATDT command to verify that a dial tome can be detected by the modem. If you do not hear a dial tone, troubleshoot the modem.

7. Terminate telnet command. From the Cisco IOS command line, press Ctrl-Shift-6, then press the x key.

8. Enter disconnect at the Cisco IOS EXEC prompt.

Router: Cisco IOS version does not support Async MPPP

Note Async MPPP requires Cisco IOS 11.0(3) or higher

1. Use show version Cisco IOS EXEC command to ensure that software is Cisco IOS 11.0(3) or higher.

2. If not, upgrade to Cisco IOS 11.0(3) or higher.

Router: Configuration problems

Ensure that the configuration conforms to the basic command setup as illustrated in the following related document:

•http://www.cisco.com/warp/public/793/access_dial/router2router.html

•http://www.cisco.com/warp/public/793/access_dial/async_multilink.html


Table 2-2 Calls fail to connect

Problem
Suggested Diagnostic Steps

Call not answered

Refer to the following related site:

•http://www.cisco.com/warp/public/112/chapter17.htm

NAS: Additional calls receive a busy signal

1. From the NAS, use the show modem summary Cisco IOS command to verify that modems are available.

See the output provided in "Cisco IOS show modem summary Command Output" for additional information.

2. Verify that there are enough modems available.

PC: Authentication failure

1. Use the debug ppp authentication Cisco IOS command to determine if authentication failures are occurring.

See the output provided in "Cisco IOS debug ppp authentication Command Output" for additional information.

2. If authentication failures are found, ensure that passwords and usernames are entered correctly.

Router: Modem failure

1. Reverse telnet to each modem separately.

Refer to the following document for notes about reverse telnet:

•http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/12cgcr/dial_c/dcrtelnt.htm

2. Enter the AT command.

3. Look for Ok response.

4. If Ok is not returned, troubleshoot hardware for other problems.

5. For routers with external modems, enter the ATM1 command to enable the modem's speaker.

6. Enter the ATDT command to verify that a dial tome can be detected by the modem. If you do not hear a dial tone, troubleshoot the modem.

7. Terminate telnet command. From the Cisco IOS command line, press Ctrl-Shift-6, then press the x key.

8. Enter disconnect at the Cisco IOS EXEC prompt.

Router: Cisco IOS version does not support Async MPPP

Note Async MPPP requires Cisco IOS 11.0(3) or higher

1. Use show version Cisco IOS EXEC command to ensure that software is Cisco IOS 11.0(3) or higher.

2. If not, upgrade to Cisco IOS 11.0(3) or higher

Router: Configuration problems

Ensure that the configuration conforms to the basic command setup as illustrated in the following related document:

•http://www.cisco.com/warp/customer/793/access_dial/router2router.html

•http://www.cisco.com/warp/customer/793/access_dial/async_multilink.html


Table 2-3 Poor performance

Problem
Suggested Diagnostic Steps

NAS: MP not bundling

Note Please refer to the following document for related information:

http://www.cisco.com/warp/public/131/mppp_bundle_name.html

1. Use the show ppp multilink Cisco IOS command at the NAS and router to determine if bundling is occurring.

See the output provided in "Cisco IOS show ppp multilink Command Output" for additional information.

2. Look for the bundle or user name. If bundling is occurring, a bundle with the associated user will appear.

3. If bundling is not occurring, use the debug ppp negotiation and debug ppp multilink events Cisco IOS commands to verify MRRU requests are occurring on both ends and whether a bundle is being created.

See the output provided in "Cisco IOS debug ppp negotiation Command Output" for additional information.

4. If MRRU requests are not occurring on either end, ensure that ppp multilink interface configuration command is configured on all required interfaces. Disconnect existing links and reconnect.

5. If MRRU requests are being exchanged, but bundling is not occurring the refer to the following documents for Cisco IOS configuration information:

–http://www.cisco.com/warp/public/793/access_dial/router2router.html

–http://www.cisco.com/warp/public/793/access_dial/async_multilink.html

NAS: Fast switching is not working.

1. Use show running-config Cisco IOS command to verify that all the applicable interfaces do not have the following command: no ip route-cache

2. If this command is included, enable the ip route-cache interface configuration command on all applicable interfaces.

NAS: Processor overhead

1. Use the show processes cpu Cisco IOS command at the NAS to determine CPU utilization.

See the output provided in "Cisco IOS show processes cpu Command Output" for additional information.

2. If top line utilization number is approaching 100 percent, investigate CPU load issue. Refer to the following URL: 

http://www.cisco.com/warp/public/63/hig
hcpu.html

PC: Dialup Networking (DUN) 1.3 or higher needed

PC DUN 1.3 was issued by Microsoft as a performance improvement over PC DUN 1.2. Refer to Microsoft technical support for additional information.

Refer to this Microsoft document for details:

•http://microsoft.com/ntserver/nts/downloads/recommended/dun13win95/ReleaseNotes.asp


Table 2-4 IP connectivity is down

Problem
Suggested Diagnostic Steps

NAS: MP not bundling

1. Use the show ppp multilink Cisco IOS command at the NAS and router to determine if bundling is occurring.

See the output provided in "Cisco IOS show ppp multilink Command Output" for additional information.

2. Look for the bundle or user name. If bundling is occurring, a bundle with the associated user will appear.

3. If bundling is not occurring, use the debug ppp negotiation and debug ppp multilink events Cisco IOS commands to verify MRRU requests are occurring on both ends and whether a bundle is being created.

See the output provided in "Cisco IOS debug ppp negotiation Command Output" for additional information.

4. If MRRU requests are not occurring on either end, ensure that ppp multilink interface configuration command is configured on all required interfaces. Disconnect existing links and reconnect.

5. If MRRU requests are being created, but bundling is not occurring the refer to the following documents for Cisco IOS configuration information:

–http://www.cisco.com/warp/customer/793/access_dial/router2router.html

–http://www.cisco.com/warp/customer/793/access_dial/async_multilink.html

Connection routing (if you cannot ping gateway from the client)

1. At the NAS, use the show ip route client_ip_address Cisco IOS command to determine whether the route exists to the remote client via the virtual access interface.

See the output provided in "Cisco IOS show ip route Command Output" for additional information.

2. If the route does show up, determine whether you can ping from a remote client to the gateway of the NAS.

3. If this ping succeeds, problem is outside the NAS.


Table 2-5 Phone calls last too long

Problem
Suggested Diagnostic Steps

PC: User not using suspend/resume button in DUN screen.

When all connections are established, you can either view status information about the link by double-clicking on the "Communicating Computers" icon displayed in the taskbar, or you may disconnect the connection. Click on "Details" to verify that the connection is using multiple devices.

When you select a device in the list box, a Suspend or Resume button appears. If a Suspend button appears, the device is now in use and bundled into the multilink connection. Clicking on the "Suspend" button disconnects that line and removes the line from the bundled connections. If the "Resume" button appears, click it to dial that connection and add that line to the bundle.

You can dynamically suspend each connection without dropping the entire multilink session.

Router: Configuration tuning problems:

•dialer load-threshold set too low

•dialer idle-timeout set too long

•Interesting traffic improperly defined

•ppp timeout multilink link remove set too long

Refer to the following document for tuning notes related to these configuration commands:

•http://www.cisco.com/warp/customer/793/access_dial/router2router.html#tuning


Table 2-6 Calling too often

Problem
Suggested Diagnostic Steps

Router: Configuration tuning problems:

•dialer load-threshold set too low

•dialer idle-timeout set too short

•Interesting traffic improperly defined

•ppp timeout multilink link add set too short

Refer to the following document for tuning notes related to these configuration commands:

•http://www.cisco.com/warp/customer/793/access_dial/router2router.html#tuning


Table 2-7 Calling too infrequently

Problem
Suggested Diagnostic Steps

Router: Configuration tuning problems:

•dialer load-threshold set too high

•Interesting traffic improperly defined

•ppp timeout multilink link add set too long

Refer to the following document for tuning notes related to these configuration commands:

•http://www.cisco.com/warp/customer/793/access_dial/router2router.html#tuning


Table 2-8 Intermittent user access

Problem
Suggested Diagnostic Steps

Too few modems for application, lines are too busy

1. From the NAS, use the show modem summary Cisco IOS command to verify that modems are available.

See the output provided in "Cisco IOS show modem summary Command Output" for additional information.

2. Verify that there are enough modems available.

PC: Multiple users with same name attempting to access central site NAS.

Note Please refer to the following document for related information:

http://www.cisco.com/warp/public/131/mppp_bundle_name.html

1. If users are dialing in from multiple client PCs with the same user name, configure the Cisco IOS command multilink bundle-name both in the central site NAS configuration. This command forces the NAS to create a bundle consisting of the user name and the endpoint discriminator of the client.

2. Use the show ppp multilink command to verify that the bundle name includes both the user name and the endpoint discriminator.

See the output provided in "Cisco IOS show ppp multilink Command Output" for additional information.

NAS: Telco hunt groups implemented at central site spanning multiple NASs.

1. Determine whether the Telco has implemented hunt groups and whether the hunt groups connect to multiple NASs at the the central site.

2. If the hunt group delivers calls to multiple NASs, then ensure that multichassis multilink PPP (MMP) is implemented correctly in the all the associated NASs.

Refer to the following three documents for MMP configuration notes:

•http://www.cisco.com/warp/public/131/3.html

•http://www.cisco.com/warp/public/793/access_dial/multilink.html

•http://www.cisco.com/warp/public/793/access_dial/6.html

•http://www.cisco.com/univercd/cc/td/doc/product/software/ios113ed/113ed_cr/dial_c/dcprt7/dcmmp.htm


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