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This Question is Not Answered 1 Correct Answer available (4 pts) 2 Helpful Answers available (2 pts)
2531 Views 6 Replies Latest reply: Oct 16, 2011 7:03 AM by Roland Schmid RSS

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Question about "frame-relay interface-dlci" command

Oct 14, 2011 10:38 PM

Jesse 1 posts since
Oct 14, 2011

I am going through the ICND2 Official Exam Certification Guide and am working on the example found on page 491 -- "Configuring the Encapsulation and LMI."  In this example there are 3 routers in a full mesh topology using only physical interfaces -- subinterfaces have *not* been configured in the example(s) up to this point.

 

The example states to change the encapsulation type for one of the 3 routers (router Raleigh, in the example) from the default ("cisco") to IETF.  On router Raleigh the interface subcommand "encapsulation frame-relay ietf" is issued.  Again this is a 3 router full mesh network, so there are two VC's per router.  Per the issued command, Raleigh is now configured to use IETF encapsulation on *both* its VC's.

 

On one of the other two routers the example shows that you must use the command "frame-relay interface-dlci 53 ietf" to specify that only the specific VC to router Raleigh is set to use IETF encapsulation, with the VC to the third router still using the default Cisco encapsulation.  The example shows that exact interface subcommand being issued, on, in this case, router Mayberry. Again, there is no indication that a sub-interface has been configured, or that the command is a subinterface subcommand.

 

And this is where I'm running into issues and have questions.  Nowhere in the text does it talk about using subinterfaces for the 2 different VC's, and in my lab I do not have the ability to enter the "frame-relay interface-dlci 'dlci#' ietf" command, as they do in the example.  In the research I have done it looks like you can only specify the encapsulation type per DLCI if you are using the command on a subinterface, with different VC's running on different subinterfaces.

 

Is there an error in the exam guide text? Or am I just completely missing something here?

 

Thanks.

  • Martin 13,892 posts since
    Jan 16, 2009
    Currently Being Moderated
    1. Oct 14, 2011 11:05 PM (in response to Jesse)
    Re: Question about "frame-relay interface-dlci" command

    That is possibility; one of many in the world of frame relay;

    full mesh topology using only physical interfaces is the easiest way to run FR as everything is automatic;

     

    Full mesh with physical interfaces means all routers must be on one and same subnet. In case of ICDN2 example, there are 2 PVCs at each router going to 2 partners over one physical link; see it with show frame-relay map and show frame-relay pvc. This means that FR Cloud switch sends you 2 pvcs, one pvc per connection or destination route.

     

    LMI types is like a langauge; rotuers must agree on one common langauage to speak; Yes, you can mix ietf and cisco but you must specify match, like R1 and R2 are over default cisco but R2 and R3 are over ietf.

     

    You could use point-to-point sub-interfaces where 1 pvc is 1 subnet reaching only one partner. in this case, you will have alos 2 pvc (get those from Cloud) but 1 pvc per link.

     

    see my example for PT https://learningnetwork.cisco.com/docs/DOC-11280

    there are many others, search my docs.

     

    Message was edited by: Martin

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  • Wendell Odom 350 posts since
    Jun 19, 2008
    Currently Being Moderated
    2. Oct 15, 2011 10:45 AM (in response to Jesse)
    Re: Question about "frame-relay interface-dlci" command

    Hi Jesse,

    Yep, that's an error. If you go to the book's page at the publisher's web site, and look at the errata, you'll see an entry for page 491 that shows the fix. The mistake: The encapsulation is changed with the frame-relay map command, not the frame-relay interface-dlci command. Sorry about the error.

    Regards,

    Wendell

     

    http://www.ciscopress.com/bookstore/product.asp?isbn=158720181X

     

    PS go to this page, click "Updates", then "download the errata".

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  • Martin 13,892 posts since
    Jan 16, 2009

    Good poinWendell, I forgot always check errata for all your books as things happen during publishing;

     

    and this is true: encapsulation type per DLCI if you use subinterface

    OR

    frame-relay map ip x.x.x.x ietf

     

    R1(config-if)#frame-relay map ip 10.1.1.1 17 ?

      broadcast            Broadcasts should be forwarded to this address

      cisco                Use CISCO Encapsulation

      compress             Enable TCP/IP and RTP/IP header compression

      ietf                 Use RFC1490/RFC2427 Encapsulation

      nocompress           Do not compress TCP/IP headers

      payload-compression  Use payload compression

      rtp                  RTP header compression parameters

      tcp                  TCP header compression parameters

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  • Roland Schmid 291 posts since
    Sep 5, 2010

    Hello,

     

    I have questions.

    Am I changing the encapsulation type only for one frame-relay map ?

    Other frame-relay maps could use default frame-relay encapsulation (cisco) ?

    LMI type on the frame-relay map with encapsulation ietf stays cisco ?

     

    Kind regards,

    Roland

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  • cadetalain 2,728 posts since
    Sep 18, 2008

    Hi,

     

    yes you can leave default encapsulation for other dlcis as long as they are for another router that supports that encapsulation.

    LMI is  for DCE-DTE so switch-router and has nothing to do with encapsulation which is a DTE-DTE concept(router-router).You must hve he same LMI type as the switch and by default routers autosense LMI type from switch and so configure themselves with same type.

     

    Alain.

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  • Roland Schmid 291 posts since
    Sep 5, 2010

    cadetalain schrieb:

     

    Hi,

     

    yes you can leave default encapsulation for other dlcis as long as they are for another router that supports that encapsulation.

    LMI is  for DCE-DTE so switch-router and has nothing to do with encapsulation which is a DTE-DTE concept(router-router).You must hve he same LMI type as the switch and by default routers autosense LMI type from switch and so configure themselves with same type.

     

    Alain.

     

    Hi,

     

    ok, thank you

     

    Kind regards,

    Roland

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