Ciscco 1700 and 2600 series router is not communicating with Cisco 3800 series

Posted on 2009-04-15
Last Modified: 2012-05-06
Hello All,

I have a wierd issue. I have one 1700 series router with a T1 wick and another 3800 series router with several T1 wick. When I connect the 1700 to the 3800 using a t1 roll over cable the serial interfaces comes up then going back down repeatedly. I tried also connecting a 2600 to the 3800 series router with the same results. I keep getting CRC errors, input, and frame errors on the connected interfaces. We connected a hard loop to the 1700 and 3800 T1 wick cards and everything is working fine. What is wierd is when I connect the 1700 series router and 2600 series router together with a T1 roll over cable, they work without issues and the interface is stable. My question is why would connected each of these routers to the 3800 produce bad results. We have other wick cards on the 3800 that are connecting to other routers without problems. I even tried a seperate interface on the 3800 with the same problem. I have included my router configurations.  
Question by:greenbeanx81
    LVL 10

    Expert Comment

    When you say "rollover" cable, what pinouts do you mean.  Typically, a "rolled"cable is used for console connections.  The pinouts for that are:

    For a T1 "crossover" cable, you need different pinouts.

    If your pinouts are correct, then you probably need to check your encapsulation settings on both ends of the cable to make sure they match.  By default, cisco routers use HDLC encapsulation.  If one end is using PPP (it looks like all your serial connections are using PPP on the Montabello router), then you would also need to use PPP on the other end (the Gendale router doesnt have the "encapsulation ppp" command configured).

    I hope this helps.

    Author Comment

    We used a T1 cross over cable with the same results. Encapsulation is set to HDLC. Still Having the same problem.
    LVL 10

    Accepted Solution

    Are these the two interfaces that you are crossconnecting?  I am guessing so because of the subnet matches.  If so, I believe that both sides or neither side of the link need to have the " service-module t1 data-coding inverted" line configured.  Not one having it and the other not.

    interface Serial2/0/0
     description T1 to Verdugo
     ip address
     service-module t1 clock source internal
     service-module t1 timeslots 1-24
    interface Serial0
     ip address
     no ip directed-broadcast
     no fair-queue
     service-module t1 clock source line
     service-module t1 data-coding inverted
     service-module t1 timeslots 1-24

    Author Comment

    Thanks you. I added the "service-module t1 data-coding inverted" but still no luck bring the lline up.


    Author Comment

    I never did find out why the routers will not talk to each other. They have no Cisco support so I guess I'll close this case.

    Write Comment

    Please enter a first name

    Please enter a last name

    We will never share this with anyone.

    Featured Post

    IT, Stop Being Called Into Every Meeting

    Highfive is so simple that setting up every meeting room takes just minutes and every employee will be able to start or join a call from any room with ease. Never be called into a meeting just to get it started again. This is how video conferencing should work!

    Suggested Solutions

    Tired of waiting for your show or movie to load?  Are buffering issues a constant problem with your internet connection?  Check this article out to see if these simple adjustments are the solution for you.
    Shadow IT is coming out of the shadows as more businesses are choosing cloud-based applications. It is now a multi-cloud world for most organizations. Simultaneously, most businesses have yet to consolidate with one cloud provider or define an offic…
    After creating this article (, I decided to make a video (no audio) to show you how to configure the routers and run some trace routes and pings between the 7 sites…
    After creating this article (, I decided to make a video (no audio) to show you how to configure the routers and run some trace routes and pings between the 7 sites…

    761 members asked questions and received personalized solutions in the past 7 days.

    Join the community of 500,000 technology professionals and ask your questions.

    Join & Ask a Question

    Need Help in Real-Time?

    Connect with top rated Experts

    6 Experts available now in Live!

    Get 1:1 Help Now