Troubleshooting Serial Lines - Internetworking Troubleshooting - page 432

In a production environment, verify that console logging is disabled. Enter the show
logging command. If logging is enabled, the access server might intermittently freeze up
as soon as the console port gets overloaded with log messages. Enter the no logging
console command.

Note

If debug isdn q921 is turned on and you do not receive any debug outputs, place a call or
reset the controller to get debug outputs.

Note

Verify that Layer 2 is stable. You should observe the debug outputs for messages indicating that the
service is not bouncing up and down. If you see the following types of debug outputs, the line is not
stable:

Step 1

Mar 20 10:06:07.882: %ISDN-6-LAYER2DOWN: Layer 2 for Interface Se0:15, TEI 0 changed
to down
Mar 20 10:06:09.882: %LINK-3-UPDOWN: Interface Serial0:15, changed state to down
Mar 20 10:06:21.274: %DSX1-6-CLOCK_CHANGE: Controller 0 clock is now selected as
clock source
Mar 20 10:06:21.702: %ISDN-6-LAYER2UP: Layer 2 for Interface Se0:15, TEI 0 changed to
up
Mar 20 10:06:22.494: %CONTROLLER-5-UPDOWN: Controller E1 0, changed state to up
Mar 20 10:06:24.494: %LINK-3-UPDOWN: Interface Serial0:15, changed state to up

If Layer 2 does not appear to be stable refer to the “Troubleshooting Error Events” section, earlier in this
chapter.

Verify that you are seeing only SAPI messages in both transmit (TX) and receive (RX) sides. Step 2

Mar 20 10:06:52.505: ISDN Se0:15: TX -> RRf sapi = 0 tei = 0 nr = 0
Mar 20 10:06:52.505: ISDN Se0:15: RX <- RRf sapi = 0 tei = 0 nr = 0
Mar 20 10:07:22.505: ISDN Se0:15: TX -> RRp sapi = 0 tei = 0 nr = 0
Mar 20 10:07:22.509: ISDN Se0:15: RX <- RRp sapi = 0 tei = 0 nr = 0
Mar 20 10:07:22.509: ISDN Se0:15: TX -> RRf sapi = 0 tei = 0 nr = 0
Mar 20 10:07:22.509: ISDN Se0:15: RX <- RRf sapi = 0 tei = 0 nr = 0

Verify that you are not seeing SABME messages, which indicates that Layer 2 is trying to reinitialize.
This is usually seen when we are transmitting poll requests (RRp) and not getting a response from the
switch (RRf), or vice versa. The following are examples of SABME messages. We should get a response
from ISDN switch for our SABME messages (UA frame received):

Step 3

Mar 20 10:06:21.702: ISDN Se0:15: RX <- SABMEp sapi = 0 tei = 0
Mar 20 10:06:22.494: ISDN Se0:15: TX -> SABMEp sapi = 0 tei = 0
If you are seeing SABME messages, do the following:

Use the show running-config command to check whether isdn switchtype and pri-group timeslots
are configured correctly. Contact your service provider for correct values.

•

To change the isdn switchtype and pri-group , use these lines:

•

maui-nas-03# configure terminal
maui-nas-03(config)# isdn switch-type primary-net5
maui-nas-03(config)# controller e1 0
maui-nas-03(config-controlle)# pri-group timeslots 1-31

Verify that the D-channel is up using the show interfaces serial x:15 command. Step 4