Learning by Doing: CISCO Certified Network ... - SCN Research

sh protocols
debug dialer packets
debug dialer
Problems that cause ISDN to not work: no cable, dialer interface shut down, dialer list
configured improperly or not at all, or problems with the dialer string/map.
Data Link layer:
Step 2: We need to see if our LAP-D and PPP are completing properly. We can use these
commands for that:
debug isdn q921
debug ppp negotiation
(LAPD)
(PPP)
Problems that cause ISDN to not work: problems with the dialer string/map, problems
with the layer 2 ISDN line, or problems with ppp.
Network layer:
Step 3: Check for confirmation of a good connection using these commands:
debug isdn q931
show isdn status
Problems that cause ISDN to not work: problems with the dialer string/map, problems
with the layer 2 ISDN line, or problems with ppp.
ISDN Network Scenarios:
Ok. Great. Now you are ready to fire up an ISDN connection and troubleshoot it with no
problems, right? Maybe. Let’s take some time to look at some of the output from these
debug and show commands. We have already seen how cryptic they can be. For these
let’s work from the network layer down. We will show a good connection and then
introduce problems and see how the debug/show commands change with problems and
what causes them.
Here is the output of each of those commands for a good working ISDN connection using
an ADTRAN between two routers. To bring the line up I pinged the BRI interface. You
can see the first ping packet does not work. It generates the interesting traffic, the BRI
line comes up and the other four succeed.
kissane#ping 192.168.1.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.1.1, timeout is 2 seconds:.!!!!
Success rate is 80 percent (4/5), round-trip min/avg/max = 32/32/32 ms
00:13:26: %LINK-3-UPDOWN: Interface BRI0/0:1, changed state to up
00:13:26: %ISDN-6-CONNECT: Interface BRI0/0:1 is now connected to
5551234
422