serial is down line protocol is down

Unanswered Question
Nov 13th, 2007

I have connected two 2600 routers back to back using DTE/DCE cable. I have set the clock rate 56000 at DCE end. I have also assinged IP addresses to the Serial interfaces. But when I connect them I get this message

'serial is down line protocol is down'

Can someone please guide me


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Overall Rating: 3 (1 ratings)
moazzamkhan Tue, 11/13/2007 - 12:36

Both are in this state. Can you please guide me what could be the reason and how this can be resolved.


erik.kneebone Tue, 11/13/2007 - 12:45

What is the clock source on both interfaces? If your trying to simulate a serial link they have to sync up to talk to each other. Set one side to internal clocking and the other to line clocking. Once you do that shut down one of the interfaces, then unshut it.

moazzamkhan Tue, 11/13/2007 - 14:29

Thank Erik

I have set the clock rate on one of the serial interfaces i.e Serial0/0 by using command

clock rate 56000 . Is that enough or do I need to do somthing else. Is this what you meant internal clocking.

How I set the other side to line clocking.

Kevin Dorrell Tue, 11/13/2007 - 15:05

Could you please check you set the clock on the DCE side. Do a show controllers for the interfaces on each side of the link. One of them should recognise a DTE cable, and the other a DCE cable. The clock needs to be set on the DCE side.

If not, please post the results of the show controllers. This is what you should see:

R2#show controllers Serial1/0

CD2430 Slot 1, Port 0, Controller 0, Channel 0, Revision 19

Channel mode is synchronous serial

idb 0x852CC47C, buffer size 1524, V.35 DTE cable

R5#show controllers Serial 2

CD2430 unit 0, Channel 0, Chip Revision 0C, Microcode 18

Channel mode is synchronous serial

idb 0x2AAC08, buffer size 1524, V.35 DCE cable, clockrate 115200

Kevin Dorrell


moazzamkhan Tue, 11/13/2007 - 15:51

Thanks Kevin

After checking the clock by using show contollers command I get this on the dce side


nterface Serial0/1

Hardware is PowerQUICC MPC86042:25.538: %LINEPROTO-5-UPDOW

DCE V.35, clock rate 56000ce FastEthern

idb at 0x8199BE8C, driver data structure at 0x819A3C28

et0/0, changed st rmd(68012700): st

SCC Registers:h 60C address

General [GSMR]=0x2:0x00000000, Protocol-specific [PSMR]=0x8

rmd(68012708): status 9000

Events [SCCE]=0x0000, Mask [SCCM]=0x0000, Status [SCC


and the output of show interfaces is


2600#show interfaces


FastEthernet0/0 is up, line protocol is up

Interface Serial0/0

Hardware is AmdFE, address is 0014.6a5b.07c0 (bia 0014.6a5b.07c0)No serial cable attached

idb at 0x819921B8,

Internet address is

MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,eneral [GSMR]=0x2:0x00000030, P output rate 0 bits/sec, 0 packets/secADIR]=0x1100, [PAPAR]=0xFFFF

0 packets input, 0 bytes, 0 no bufferADAT]=0x

Serial0/1 is administratively down, line protocol is down 7C66984

Hardware is PowerQUICC Serial2610#



MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,

Interface FastEthernet0/0

Last clearing of "show interface" counters never

Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0, CXDA =0x00000000

Queueing strategy: weighted fair000000 (half-duplex)

keller.oliver Tue, 11/13/2007 - 22:59

Serial0/1 is administratively down, line protocol is down

Are you sure that you really issued the "no shutdown" command in the serial0/1 config sub-mode ?

administratively down normally appears after you issue the "shutdown" command.

Sorry if this is too trivial, but it's the first thing that comes to mind :)



bvsnarayana03 Tue, 11/13/2007 - 23:03

This message indicates clearly problem at physical layer. Pls check if the cables are properly connected, & that the ports are not shutdown.

desai.jaideep Tue, 11/13/2007 - 23:33


What is the hardware config for both the routers?

Are you sure you are connecting s0/1 of one router to s0/1 of other?

B'coz in show statement, one s0/1 is administratively down......

Can you pls provide "show ver" and "sh run"?



desai.jaideep Wed, 11/14/2007 - 00:33

Hey Kevin,

How do you get these bold characters?

I was unable to do so..... :)


Kevin Dorrell Wed, 11/14/2007 - 02:12

They are just HTML tags. The forum accepts a limited range of them. For bold, start with this without the spaces: < b >, and to end it < / b >.

You can use "u" for underline.

You can put "& n b s p ;" at the beginning of a line to indent it, but it strips it each time you edit the posting so you have to put it in again by hand.

So, let's see if adding the spaces has fooled it into printing the tags literally rather than tagging my whole posting! So, it is OK.

The one I wish they would implement is "".

Kevin Dorrell



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