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New Member

Keeping interface UP

I have a trouble with keeping the interface UP.

I need that Serial interface should be UP.

So I use the following commands:


cisco#config t

cisco(config)#interface serial 0

cisco(config-if)#ip address

cisco(config-if)#clock rate 64000

cisco(config-if)#no shutdown

Now when I shoot these commands below:



It then shows Serial Down.

What am I doing wrong. What do I need to make this interface UP.


New Member

Re: Keeping interface UP

Down and shutdown are 2 different things...

Do you have an active connection plugged into the serial interface? Also, if you do a sh int s0 does it show up/down or down/down?

The interface will always be 'down' if nothing is plugged into it.



Hall of Fame Super Bronze

Re: Keeping interface UP

How is the other side configured ?

You are entering the clock rate, so I assume this interface is the DCE side ?

You can verify this by issuing:

sh controllers s0/0 | i DCE|DTE

If it's a DTE, you don't need a clock rate command.

You must also match the encapsulation between the 2 devices.

Currently, you are running the default - HDLC.


Re: Keeping interface UP

What type of Serial connection is this? It looks like an in-house line since you are providing clock. Does your line come from the carrier? If so they are most likely providing a clock source for it. Also can you provide a SHOW INTERFACE SERIAL 0 results for us to look at. Do you have all your control signals from your DCE equipment???

New Member

Re: Keeping interface UP

Router#show interface serial 0

Serial0 is down, line protocol is down

Hardware is HD64570

Internet address is

MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, rely 255/255, load 1/255

Encapsulation HDLC, loopback not set, keepalive set (10 sec)

Last input never, output never, output hang never

Last clearing of "show interface" counters never

Input queue: 0/75/0 (size/max/drops); Total output drops: 0

Queueing strategy: weighted fair

Output queue: 0/1000/64/0 (size/max total/threshold/drops)

Conversations 0/0/256 (active/max active/max total)

Reserved Conversations 0/0 (allocated/max allocated)

5 minute input rate 0 bits/sec, 0 packets/sec

5 minute output rate 0 bits/sec, 0 packets/sec

0 packets input, 0 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

0 packets output, 0 bytes, 0 underruns

0 output errors, 0 collisions, 8 interface resets

0 output buffer failures, 0 output buffers swapped out

0 carrier transitions

DCD=down DSR=down DTR=down RTS=down CTS=down

I use Console cable to connect to the router

New Member

Re: Keeping interface UP

The router is connected to my computer

Hall of Fame Super Bronze

Re: Keeping interface UP

The serial interface needs to connect to another serial interface device, until then - the interface will be down/down.


Re: Keeping interface UP

Since you are supplying clock from the interface and you also do not show any control signals up (from your show interface serial command). Make sure you have the correct cable off the router. It must be a DCE. Also may I ask why are you sending a serial connection to your computer? Is this some special application??

New Member

Re: Keeping interface UP

I am just practising some cisco commands by connecting my pc with the router ..

I am using HyperTerminal as a terminal interface program

Hall of Fame Super Bronze

Re: Keeping interface UP

That's a console connection, interfaces on a router will only go up if you connect a device at the other end.

On this case, you need another router and a serial cable between the two.

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