Status Line Condition Possible Problem Solution
Serial x is up,
line protocol
is up
---
This is the proper status line condition. No action required.
Serial x is down,
line protocol is
down (DTE
mode)
Typically indicates that
the router is not sensing
a CD signal (that is,
CD is not active).
a.. Telephone company
problem---Line is
down or line is not
connected to
CSU/DSU
b.. Faulty or incorrect
cabling
c.. Hardware failure
(CSU/DSU)
Step 1 Check the LEDs on the CSU/DSU to see whether CD is active, or
insert a breakout box on the line to check for the CD signal.
Step 2 Verify that you are using the proper cable and interface (see
your hard- ware installation documentation).
Step 3 Insert a breakout box and check all control leads.
Step 4 Contact your leased-line or other carrier service to see whether
there is a problem.
Step 5 Swap faulty parts.
Step 6 If you suspect faulty router hardware, change the serial line to
another port. If the connection comes up, the previously connected interface
has a problem.
Serial x is up,
line protocol is down (DTE mode)
a.. Local or remote router
is misconfigured
b.. Keepalives are not
being sent by
remote router
c.. Leased-line or
other carrier
service problem---noisy
line, or misconfigured
or failed switch
d.. Timing problem
on cable (SCTE
not set on CSU/DSU)
e.. Failed local or
remote CSU/DSU
f.. Router hardware
failure (local or
remote)
Step 1 Put the modem, CSU, or DSU in local loopback mode and use the
show
interfaces serial command to determine whether the line protocol comes up.
If the line protocol comes up, a telephone company problem or a failed
remote router is the likely problem.
Step 2 If the problem appears to be on the remote end, repeat Step 1 on
the remote modem, CSU, or DSU.
Step 3 Verify all cabling. Make certain that the cable is attached to
the correct interface, the correct CSU/DSU, and the correct telephone company
network termination point. Use the show controllers exec command to determine
which cable is attached to which interface.
Step 4 Enable the debug serial interface exec command.
Caution: Because debugging output is assigned high priority in the CPU
process, it can render the system unusable. For this reason, use debug
commands only to troubleshoot specific problems or during troubleshooting
sessions with Cisco technical support staff. Moreover, it is best to use
debug
commands during periods of lower network traffic and fewer users. Debugging
during these periods decreases the likelihood that increased debug command
processing overhead will affect system use.
Serial x is up,
line protocol is down (DTE mode)
Step 5 If the line protocol does not come up in local loopback mode and
if the output of the debug serial interface exec command shows that the
keepalive counter is not incrementing, a router hardware problem is likely.
Swap router interface hardware.
Step 6 If the line protocol comes up and the keepalive counter
increments, the problem is not in the local router.
Step 7 If you suspect faulty router hardware, change the serial line to
an unused port. If the connection comes up, the previously connected
interface
has a problem.
Serial x is up,
line protocol is down (DCE mode)
a.. Missing clockrate
interface configuration
command
b.. DTE device does not
support or is not
set up for SCTE
mode (terminal
timing)
c.. Failed remote
CSU or DSU
d.. Failed or incorrect
cable
e.. Router hardware
failure
Step 1 Add the clockrate interface configuration command on the serial
interface.
Syntax:
clock rate bps
Syntax Description:
bps---Desired clock rate in bits per second: 1200, 2400, 4800, 9600,
19200, 38400, 56000, 64000, 72000, 125000, 148000, 250000, 500000, 800000,
1000000, 1300000, 2000000, 4000000, or 8000000.
Step 2 Set the DTE device to SCTE mode if possible. If your CSU/DSU
does
not support SCTE, you might have to disable SCTE on the Cisco router
interface.
Step 3 Verify that the correct cable is being used.
Step 4 If the line protocol is still down, there is a possible hardware
failure or cabling problem. Insert a breakout box and observe leads.
Step 5 Replace faulty parts as necessary.
Serial x is up,
line protocol is up (looped)
Loop exists in
circuit. The sequence
number in the
keepalive packet
changes to a random
number when a loop
is initially detected.
If the same random
number is returned
over the link, a
loop exists.
Step 1 Use the show running-config privileged exec command to look for
any loopback interface configuration command entries.
Step 2 If you find a loopback interface configuration command entry,
use
the no loopback interface configuration command to remove the loop.
Step 3 If you do not find the loopback interface configuration command,
examine the CSU/DSU to determine whether they are configured in manual
loopback mode. If they are, disable manual loopback.
Step 4 Reset the CSU or DSU and inspect the line status. If the line
protocol comes up, no other action is needed.
Step 5 If the CSU or DSU is not configured in manual loopback mode,
contact the leased-line or other carrier service for line troubleshooting
assistance.
--
Sincerely,
Peter Kurdziel
CCNA, CCDA, 1/4 CCNP (BCSN), MCSE, MCP+i
Flash: www.inotez.com
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Email: [EMAIL PROTECTED]
""Tariq"" wrote in message
[EMAIL PROTECTED]">news:[EMAIL PROTECTED]...
> Hello Everybody.
>
> I am getting very strange problem in my home network.
> I am getting Status is up and line protocol is down message.
>
> Please check the attached diagram. I am unable to coonect Serial 1 of
Router
> 2 with Serial 1 of router 3
>
> I applied clock rate 64000 command on serial 1 interface of Router 2.
> Encapsulation on both ends is HDLC.
> I changed keepalive but was no success. Default keepalive is 10.
>
> Cable and interface is is 100% ok thats why status is up. Line Protocol is
> down means that there is some problems on datalink layer.
>
> I think that it could be some masking problem. Please see it and let me
> know.
>
> Thanks
>
> Tariq
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