Line protocol question

[hyperkarma]

Okay, this might seem like a really stupid question but it's got me stumped.

What the hell does "line protocol down" mean and how the hell do I fix it? I'm using a Cisco 2500 series router, and it's occuring on serial port 0 on BOTH routers. I've checked, double checked, re double checked, and triple checked (quadruple checked?) the wiring and the physical wiring is fine...

Can anyone provide any insights to this at all for me? I'd greatly appreciate it.

TIA

[Richard Burts]

The line protocol state (up or down) reflects the layer 2 status of the interface. If your serial interface is saying that its state is up/down it means that it knows that it is plugged into something on the interface but that there is a layer 2 connectivity problem.

The nature of how the router determines the layer 2 status depends somewhat on the type of interface. On Serial interfaces the determination is based on the keepalives. So basically what the router is saying is that keepalives are not working on the router. There are a couple of things that can prevent keepalives on the serial interface, such as different protocols being configured (one end may be Cisco HDLC and the other end is PPP). If it was Frame Relay a mismatch of LMI type may cause it. Given your comment about using 2500 and that both sides are showing protocol down I am going to guesss that you have the routers configured back to back. And I am going to guess that you have not configured clock rate on whichever router has the DCE serial cable connected. When routers are back to back and do not connect to provider equipment, you need one of them to generate clocking (and it needs to be the one with the DCE cable). So check your cables, find which one is DCE, and configure clock rate on that router.

HTH

Rick

[hyperkarma]

Thanks, that cleared everything right up :)

[shadowman724]

hello,

i am working on a Boson Netsim simulator. i encountered the "interface is down..line protocol is down" problem with a fast Ethernet interface of a 1720 cisco router.

i tried the shut/no shut command in vain.

the other end of the line is a fast Ethernet interface of a 1912 switch.

i still can't understand the issue.

-Wassim-

[Richard Burts]

Wassim

Is there any chance that the interface on the other end of the connectin is shutdown?

HTH

Rick

[shadowman724]

yes both of the two end interfaces are down...down

i did "shut / no shut" for both of them. but nothing works.

is it a problem of my Boson simulator?