ignore-dcd command does not work on a cisco 805 router

[narcis antonie]

i have a cisco 805 router conected to a DCE device that does not transmit the dcd signal. i have issued the ignore-dcd command but it does not work (the status is up but the protocol is down). other routers series (like 1700) work fine after issuing the ignore-dcd command (status up, protocol up) on the same DCE device interface.

what could be the problem and how can it be solved?

thanks in advance.

[paolo bevilacqua]

If you have interface up, protocol down, it is not a DCD problem.

DCD down would cause down/down.

[narcis antonie]

hello, thanks for answering.

when i issue the sh int serial command it shows me that the dcd signal is down.

the problem is that when i connect another router on the same wire the interface goes up/up.

[margalla · Accepted solution]

Is DSR up? I guess it is since you say ignore-dcd works for other routers.

If so, then jumper DSR to DCD on the plug connected to the 805.

[narcis antonie]

yep the DSR is up. so if i connect the DSR to the DCD on the wire it should get the DCD up and it should work, right?

i will try this the next time i go to work. thanks.

[margalla]

yep the DSR is up. so if i connect the DSR to the DCD on the wire it should get the DCD up and it should work, right?

Now that I think about it, maybe not.  Like Paolo said in the first reply, if DCD is down and ignore-dcd isn't working the interface should be down/down.

If you do "no ignore-dcd" does the status change from up/down to down/down and then to up/down when you reapply it. If so then ignore-dcd is working, as far as that goes.

If the interface is up/down then what's down is the protocol on the circuit and what that means depends on what serial line protocol you are using.

If it's HDLC, line protocol depends on exchanging keepalive frames with the other end of the link.

If it's frame-relay then line protocol depends on exchanging LMI messages with the frame switch.

If it's PPP then line protocol depends on negotiating LCP with the peer.

It's probably worth jumpering DSR to DCD anyway. If it still is up/down then you need to start comparing the other interface configuration between the 805 and the 1700 where it works.

Another thing you note is that the 805 serial port will only run at speeds up to 512kbps.

[narcis antonie]

It worked. After i connected a jumper between pin 6 (DSR) and pin 8 (DCD) the interface became instantly up/up and the link started to work properly.

The 805 router was executing the ignore-dcd command but from some reason i don't yet understand the ppp protocol was not allowing the protocol to go up. With other type of router (cisco2600) this did not happen. I tried to change the protocol from ppp to hdlc on both routers and the interface status started fluctuating from up/up to up/down but the link did not work even if the status was up/up. Only after conecting pin 6 to pin 8, on the c805 router end, the link started working properly with both encapsulation protocols.

Thanks for answering, maybe this will help someone else in the future.