Troubleshooting

This chapter provides information about product issues in the Cisco 677 asymmetric digital subscriber line (ADSL) Discrete Multi-Tone (DMT) router.

4.1 WAN Link and Power-Up Issues

When you power up the router, this is the normal sequence of events:

The ALARM light comes on within five seconds, flashes for half a second, then goes off.
Between 1 and 10 seconds after the ALARM light goes off, the WAN-LNK light starts blinking, indicating that the router is attempting to establish communication with the service provider modem in the central office. After communication is established, the WAN-LNK becomes solid.

So under normal conditions, the ALARM light should be off within six seconds of powering up the router, and within one minute the WAN-LNK light should become solid.

If the router cannot establish communication with the service provider modem, the WAN-LNK light will go off and the router will wait 10 seconds. The WAN-LNK light will start blinking when the router tries again to establish communication.

If, after repeated attempts to establish communication, the WAN-LNK light continues blinking, turn the power off and then on. If the WAN-LNK light still does not become solid within one minute, call your service representative.

If the ALARM light flashes RED or lights RED and stays on, call your service representative.

Note With the POWER light ON, the WAN-LNK light may appear OFF under certain circumstances, even though the Cisco 677 is operating correctly. This condition can occur, for instance, if there is no data traffic across the WAN-LNK for two minutes or more. In this case, the PPP session will time out and the WAN-LNK light will go off. During subsequent requests for data across the link, the WAN-LNK light should start to blink, indicating that the ADSL connection sequence has started.

4.2 Web Browser Compatibility

Netscape 3.01 or higher or Internet Explorer 3.01 or higher are recommended for use as browsers for the Cisco Web Management Interface.

4.3 Serial Buffer Overflow

When using the serial port as your terminal connection, large amounts of serial data may overflow the serial buffer. This results in ASCII garbage appearing to the screen but does not affect performance or operation in any way. To avoid this issue, use Telnet to manage the Cisco 677.

4.4 RADIUS Password and Username Lengths

The Cisco 677 supports RADIUS passwords with more than 16 characters, however, RADIUS servers only support 16 characters or less. RADIUS usernames can be up to 255 characters. Refer to the "RADIUS Client" section.

4.5 Computers Running Linux Without term/termcap

Computers running Linux without the term/termcap database installed will have trouble connecting to Cisco equipment. The message "BAD ADDRESS" is sometimes displayed as an error message. The term/termcap database can be installed from the Linux install disks or CD-ROM.

4.6 Clearing PC Cache with ARP

If you update IP addresses on many Cisco 677s in rapid succession using a Windows PC, the ARP cache on the PC might not clear right away. This causes communications problems with the subsequent Cisco 677s in the line. To clear the PC cache, use the following command at the MS-DOS prompt on your PC:

c:\> arp -d 192.168.0.100

This deletes the MAC address and causes IP to send an ARP request (or packet) to the IP address 192.168.0.100. The ARP utility comes with Windows 95, Windows 98 and Windows NT, so if you don't have it in your current installation, you can install it from your original Windows install media.

4.7 RIP and Idle Timeouts

On a busy network with many RIP broadcasts and requests, RIP traffic alone can cause the Cisco 677 to remain sufficiently active to not trigger the idle timeout. Cisco recommends that RIP be disabled if Cisco 677 idle timeouts are used.

4.8 ADSL Parameters for the set interface command

The set interface wan0 command supports:

stay

Sets stay-trained mode. ADSL line will not retrain.

overhead-framing mode-number

Configures the requested ATM framing structure. The Cisco 677 supports ATM overhead framing modes 1-3. A retrain is required to negotiate the new overhead framing mode with the central office equipment. This command can be saved in NVRAM.

trellis-coding {enabled | disabled}

Configures the device to request trellis coding on the wan0 interface. Trellis coding can be enabled or disabled. A retrain is required to negotiate trellis coding with central office equipment. This command can be saved in NVRAM.

4.9 Frequently Asked Questions about the WAN LNK LED

The list in this section describes all known conditions indicated by the WAN LNK LED.

If the WAN LNK LED blinks continuously and never stays solid on, the Cisco 677 never trains to a system such as the Cisco 6xxx series:
If the Cisco 677 trains up and the WAN LNK LED turns off after approximately 105 seconds when the Cisco 677 is in routing mode, this means that the Cisco 677 PPP requests are not getting answered by the router on the service provider's network, such as the Cisco 7200 or Cisco 6400. It takes 105 seconds for three PPP requests to be sent from the Cisco 677, and if they are not answered by the Cisco 7200 or Cisco 6400, the Cisco 677 stops sending them and the WAN LNK LED turns off. There are a number of possibilities why this would happen:

: Use the show errors command to check the contents of the error log.

If the Cisco 677 trains up and the WAN LNK LED turns off, this is a sign of no ATM cell delineation.Verify that you have the ATM link terminated at the central office end. Without ATM cell delineation , the router will attempt to retrain the line in 1 to 10 seconds.
If the Cisco 677 trains up and then immediately drops the connection, the near-end DMT firmware may not be compatible with the far-end DMT firmware . For example an ITU G.Lite router may not train to an ANSI Issue 1 central office. To see the DMT firmware version installed on your router, use the show version command.
If the WAN LNK LED turns off after the Cisco 677 has successfully been transferring data end-to-end for some time, this means that the Cisco 677 or the Cisco 7200 or Cisco 6400 might have a timeout set. Use the show errors command to see if the error log shows that timeouts caused the drop. There are two timeouts that could affect the WAN LNK LED:
- IDLE timeout: This timeout can be set on the Cisco 677 or the Cisco 7200 or Cisco 6400. If the IDLE timeout is set to some value, then the Cisco 677 WAN LNK LED will turn off if the Cisco 677 becomes idle for that specified period of time. The show timeout command will display the current timeout status and settings.
- SESSION timeout: This timeout can be set on the Cisco 677 or the Cisco 7200 or Cisco 6400. If the SESSION timeout is set to some value, then the Cisco 677 WAN LNK LED will turn off after that certain period of set time no matter if it idle or not. The show timeout command will display the current timeout status and settings.
If the WAN LNK LED goes solid for approximately four seconds and then turns off, this primarily points to a RADIUS problem. After the Cisco 677 trains and the Cisco 7200 or Cisco 6400 that is being used to authenticate its PPP session is using RADIUS, then this could point to a failed RADIUS authentication. Possible reasons for a failed RADIUS authentication:

: Disabling RADIUS on the Cisco 7200 or Cisco 6400 would be a simple test to see if it is a RADIUS problem. Note that RADIUS is an application only available in routing mode.

In addition to the show errors command, you can use the show interface wan0 command to determine the cause of a retrain, or loss of service. The show interface wan0 command provides feedback on the wan0 configuration as well as the actual configuration negotiated with the central office equipment as shown below:

show interface wan0
wan0   ADSL Physical Port
       Line Trained
       Data rate     5952 Kbps down;    608 Kbps up
       Line capacity 6464 Kbps down;    672 Kbps up
       SNR Margin       5 dB; previous    5 dB
       Attenuation   12.5 dB; previous 12.5 dB
Status:
   Last Self-Test Result:Not Available
   Modem Microcode:      0x2019be18
Configured:
   Trellis Coding:          Enabled
   Echo Cancellation:      Disabled
   FDQ Adaptation:          Enabled
   Rate Adaptation:          Normal
   Overhead Framing:         Mode-3
   Bit-Swapping:           Disabled
   ATM Payload Scrambling:  Enabled
   PGA-Cutback:                0 dB
Actual:
   FEC Redundancy Bytes:
      Interl. Path:   downstream:   16, upstream     8
         Fast Path:   downstream:    0, upstream     0
   Interleave Depth:  downstream:   64, upstream     8
   Trellis Coding:         Not-Used
   Echo Cancellation:      Not-Used
   FDQ Adaptation:           In-Use
   Overhead Framing:         Mode-1
   Bit-Swapping:           Not-Used
Last Line Fault:  NONE
ATM Statistics:
   Interleaved-Path Counters:
      HEC errors:                 0
      LOCD events:                0
   Fast-Path Counters:
      HEC errors:                 0
      LOCD events:                0
DSL Statistics:
   Superframes:               26291
   Corrected Superframes:      3875
   Uncorrected Superframes:       0
   LOCD Retrains:                 0
   LOS Retrains:                  0
   LOF/RFI Retrains:              0
   ES Events:                     0
   Time Trained (h:m:s)      0:07:33

stay	Sets stay-trained mode. ADSL line will not retrain.
overhead-framing mode-number	Configures the requested ATM framing structure. The Cisco 677 supports ATM overhead framing modes 1-3. A retrain is required to negotiate the new overhead framing mode with the central office equipment. This command can be saved in NVRAM.
trellis-coding {enabled \| disabled}	Configures the device to request trellis coding on the wan0 interface. Trellis coding can be enabled or disabled. A retrain is required to negotiate trellis coding with central office equipment. This command can be saved in NVRAM.

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Troubleshooting