CCNA Complete Guide 2nd Edition.pdf - Cisco Learning Home

Troubleshooting ISDN Layer 2
- Understanding the output messages of the debug isdn q921 command is vital in
troubleshooting ISDN Layer 2 Firstly, issue the debug isdn q921 to enable the ISDN Layer 2
debugging which provides the details of ISDN Layer 2 transactions between the router and the
Telco ISDN switch. Subsequently, issue the clear interface bri {num} or clear interface
serial {num:15} privileged command to reset the ISDN interface which forces the router to
renegotiate ISDN Layer 2 information with the Telco ISDN switch.
- Below shows the sample output messages of the debug isdn q921 command:
Router#debug isdn q921
debug isdn q921 is ON.
Router#
Router#sh isdn status
Global ISDN Switchtype = basic-net3
ISDN BRI0/0 interface
dsl 0, interface ISDN Switchtype = basic-net3
Layer 1 Status:
ACTIVE
Layer 2 Status:
TEI = 76, Ces = 1, SAPI = 0, State = TEI_ASSIGNED
Layer 3 Status:
0 Active Layer 3 Call(s)
Active dsl 0 CCBs = 0
The Free Channel Mask: 0x80000003
Total Allocated ISDN CCBs = 0
Router#
Router#clear int bri0/0
Router#
23:20:28: ISDN BR0/0 Q921: User TX -> IDREQ ri=24872 ai=127
23:20:28: ISDN BR0/0 Q921: User RX SABMEp sapi=0 tei=75
23:20:28: ISDN BR0/0 Q921: User RX RRf sapi=0 tei=75 nr=0
23:20:48: ISDN BR0/0 Q921: User RX