System information

Troubleshooting X.25 Connections 19-415
X.25: No Connections over X.25 Link
The [no] debug lapb command displays information on the X.25 Layer 2 protocol. It is useful to
users who are familiar with LAPB. You can use the debug lapb command to determine why X.25
interfaces or LAPB connections are going up and down. It is also useful for identifying link
problems, as evidenced when the show interfaces command displays a large number of rejects or
frame errors over the X.25 link.
Note Exercise care when using debug commands. Many debug commands are processor intensive
and can cause serious network problems (such as degraded performance or loss of connectivity) if
they are enabled on an already heavily loaded router. When you finish using a debug command,
remember to disable it with its specific no debug command (or use the no debug all command to
turn off all debugging).
Figure 19–6 shows the output of the X.25 version of the show interfaces serial exec command and
indicates the important fields.
Figure 19-6 Output from the X.25 Version of the show interfaces serial Command
X.25: No Connections over X.25 Link
Symptom: Connections over an X.25 link fail.
Table 19–1 outlines the problems that might cause this symptom and describes solutions to those
problems.
Table 19-1 X.25: No Connections over X.25 Link (continued)
Serial0 is up, line protocol is up
Hardware is MCI Serial
Internet address is 131.63.125.14 255.255.255.0
MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, rely 255/255, load 1/255
Encapsulation X25, loopback not set
LAPB DTE, state CONNECT, modulo 8, k 7, N1 12056, N2 20
T1 3000, interface outage (partial T3) 0, T4 0
VS 1, VR 1, Remote VR 1, Retransmissions 0
IFRAMEs 1/1 RNRs 0/0 REJs 0/0 SABM/Es 1/0 FRMRs 0/0 DISCs 0/0
X25 DTE, address 170093, state R1, modulo 8, timer 0
Defaults: cisco encapsulation, idle 0, nvc 1
input/output window sizes 2/2, packet sizes 128/128
Timers: T20 180, T21 200, T22 180, T23 180, TH 0
Channels: Incoming-only none, Two-way 5-1024, Outgoing-only none
RESTARTs 1/1 CALLs 0+0/0+0/0+0 DIAGs 0/0
Last input 0:37:35, output 0:37:33, output hang never
Last clearing of "show interface" counters never
Output queue 0/40, 0 drops; input queue 0/75, 0 drops
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
4 packets input, 13 bytes, 0 no buffer
Received 0 broadcasts, 0 runts, 0 giants
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
4 packets output, 33 bytes, 0 underruns
0 output errors, 0 collisions, 85547 interface resets, 0 restarts
1 carrier transitions
Retransmit requests
Disconnect
count
Frame reject protocol errors
Connect attempts
X.25 service
initialization
"Not ready"
flow control count
LAPB state