10-15-2009 03:58 PM - edited 03-04-2019 06:23 AM
Hey guys
In my CCNP study lab I have a couple 2502's that I'm trying to connect with a back-to-back serial cable. Got a clockrate configured on the DCE end, they both have ppp encapsulation configured, except the line protocol isn't coming up.
It says:
R8#sh int s0
Serial0 is up, line protocol is down (looped)
Hardware is HD64570
Internet address is 131.109.255.10/30
MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation PPP, LCP Listen, loopback not set
Keepalive set (10 sec)
Last input 00:00:04, output 00:00:04, output hang never
Last clearing of "show interface" counters 06:41:27
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
40 packets input, 560 bytes, 0 no buffer
Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
40 packets output, 560 bytes, 0 underruns
0 output errors, 0 collisions, 4 interface resets
0 output buffer failures, 0 output buffers swapped out
0 carrier transitions
DCD=up DSR=up DTR=up RTS=up CTS=up
What does that mean, line protocol is down (looped)? What causes that? How do I fix it?!?
Thanks.
10-15-2009 05:27 PM
The back-to-back cable has a DTE end and a DCE end ... check to make sure you have them connected to the right ports (i.e., check the labels, and / or swap ends on the cable).
10-15-2009 05:29 PM
Done. Configured a clockrate on the interface with the DCE end plugged into it.
Tried different cables; problem persists.
10-16-2009 01:18 AM
Hello Stuey,
looped means the router receives its own keepalives back.
you can verify using:
debug serial interface
debug PPP negotiation
the second debug should complain about a duplicated magic number detected.
you see that the number of input packets = number of output packets.
check the other router configuration and cable plugging.
see if any loop command is present on the other router interface.
Hope to help
Giuseppe
10-15-2009 08:54 PM
What does your debug output show? Remember, debug is your friend!
This link also has some great info I didnt know:
http://www.sadikhov.com/forum/index.php?showtopic=78839
10-16-2009 02:23 AM
Means router is seeing his own packets.
Try HDLC first.
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