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18218 Views 15 Replies Latest reply: May 20, 2010 9:53 AM by Keith Barker - CCIE RS/Security, CISSP RSS 1 2 Previous Next

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frame-relay map ip command

May 13, 2010 2:25 PM

networkguy09 7 posts since
Feb 4, 2010

Information:

 

RouterA-(DLCI 100)--------(Frame Relay Cloud)---------(DLCI 200)-RouterB

 

RouterA# show run

 

<some output text omitted>

 

interface serial0/0

bandwidth 64

ip address 172.16.100.2 255.255.255.0

encapsulation frame-relay

frame-relay map ip 172.16.100.1 200 broadcast

 

Question: Router A is unable to reach RouterB. Based on the above information, what is most likely the cause of the problem?

 

Answer:

incorrect map statement

 

The local DLCI from RouterA to Frame-relay cloud is 100, which is 200 from RouterB to FR cloud. The local DLCI FR mapping from RouterA to RouterB is as follows: frame-relay map ip 172.16.100.1 100 broadcast.

 

 

 

 

Is the above answer correct?

  • Keith Barker - CCIE RS/Security, CISSP 5,351 posts since
    Jul 3, 2009
    Currently Being Moderated
    1. May 13, 2010 3:00 PM (in response to networkguy09)
    Re: frame-relay map ip command

    Yes, the answer is correct.

     

     

    Think of the PVC as a pipe with 2 ends.  (that part is not so hard to imagine.   It is called a PVC after all. )

     

    Imagine that you are at one end of the pipe, and I am at the other.     The label or DLCI the provider has given me for my end of the pipe is 22.   The label the provider has given to your end of the pipe is 33.     My IP address is 10.0.0.22.   Your IP address is 10.0.0.33.   For you to send a packet to me (destined for 10.0.0.22), you would need to send the frame on the PVC that goes to me.   The PVC that goes to me is the one with your local DLCI of 33.

     

    Think of the DLCI number as a freeway on-ramp.   That is all it is.

     

    The frame map on your router would be:

     

    frame map ip 10.0.0.22 33 broadcast  (using your DLCI 33 as an onramp to reach me at 10.0.0.22)

     

    The frame map on my router would be

     

    frame map ip 10.0.0.33 22 broadcast (using my DLCI 22 as an onramp to reach you at 10.0.0.33)

     

    Best wishes,

     

    Keith

  • Angela 746 posts since
    Jan 29, 2010
    Currently Being Moderated
    2. May 13, 2010 7:59 PM (in response to networkguy09)
    Re: frame-relay map ip command

    Hi, Keith,

     

      I have to say that I disagree, DLCI is only locally significant unless you are using global DLCI, which is not specified in this case. As for a local DLCI, the DLCI is how your router send and get traffic from the Frame Relay cloud. So, I agree with the answer that RouterA should have a DLCI of 100.

     

    Please correct if there is anything wrong,

     

    Regards,

    Angela

  • Keith Barker - CCIE RS/Security, CISSP 5,351 posts since
    Jul 3, 2009
    Currently Being Moderated
    3. May 13, 2010 9:35 PM (in response to Angela)
    Re: frame-relay map ip command

    Hello Angela -

     

    For the CCNA level, the primary focus will be a locally signifcant DLCI, hence the analogy of the onramp. 

     

    Angela, you are right about an option in frame for a Global DLCI.

     

    Thank you,

     

     

    Keith

  • Angela 746 posts since
    Jan 29, 2010
    Currently Being Moderated
    4. May 13, 2010 10:57 PM (in response to networkguy09)
    Re: frame-relay map ip command

      I'm sorry, Keith, I thought you said the answer is wrong, that's why I said "I disagree". It turns out I wasn't fully awaken, I apologize for my careless mistake....

     

    Regards

  • Scott Morris - CCDE/4xCCIE/2xJNCIE 8,396 posts since
    Oct 7, 2008
    Currently Being Moderated
    6. May 17, 2010 5:11 AM (in response to networkguy09)
    Re: frame-relay map ip command

    I'd say the logic is good there based on how I'm reading the diagram.

     

    "show frame pvc" will certainly tell us 100% on that one!

     

    HTH,

     

    Scott

  • Scott Morris - CCDE/4xCCIE/2xJNCIE 8,396 posts since
    Oct 7, 2008
    Currently Being Moderated
    7. May 17, 2010 5:17 AM (in response to networkguy09)
    Re: frame-relay map ip command

    The Mayberry router is using Mount Pilot's IP and DLCI. Am I just totally missing something here? A few other points come to mind when looking at this example and the earlier question.

     

    1. In the earlier question there is no "no frame-relay  inverse-arp" command. Is this command no longer needed once the frame-relay map command is used?
    2. No IP address is shown on the book example configuration.

     

    Unless there's another diagram, things are a little wierd there.  But look at your first set of responses with inverse arp:

     

    Router Mayberry (DLCI 51) ------ Frame Relay Cloud  ------Router Mount Pilot (DLCI 52)

     

    <--- status DLCI 52 Up                                                status DLCI 51 Up --->

     

    ------------------------------------------> I-ARP I am 199.1.1.1.1 --------------------------------------------->

     

    <------------------------------------------ I-ARP I am  199.1.1.1.2 <---------------------------------------------

     

    The fact that Mayberry receives a message saying "DLCI 52 Up" tells me that 52 is really local to that side.  Which makes the first/initial line of text very confusing to interpret!  Just bad tech editing IMHO!

     

     

     

     

    With no ip address shown on either side, it will be difficult to have pings actually work! 

     

     

    Encapsulations are end to end.  So each side would choose one.  Cisco is the default method on Cisco routers (go figure).  Encapsulation is use to determine how the frames are sent.  LAPF is a control mechanism.  While it's part of the FRF standards, it is independent of the "encapsulation" used here.

     

     

    HTH,

     

    Scott

  • Angela 746 posts since
    Jan 29, 2010
    Currently Being Moderated
    9. May 17, 2010 7:21 AM (in response to networkguy09)
    Re: frame-relay map ip command

    Hi,

     

      Can you double check this is not a global DLCI? Global DLCI certainly means different than local DLCI. I'm absolutely sure that Wendell Odom mentioned it somewhere in his book. It has a different representation than local DLCI too.

     

    Regards

  • Keith Barker - CCIE RS/Security, CISSP 5,351 posts since
    Jul 3, 2009
    Currently Being Moderated
    12. May 17, 2010 4:14 PM (in response to networkguy09)
    Re: frame-relay map ip command

    Hey Networkguy -

     

    I know you have had a ton of great feeback on this question. 

     

    Just to summarize, and put a nail in the coffin, here is a brief video that discusses it, and demonstrates it too.

     

    Double click the video to make it bigger.

     

    This file is available in my documents section on this forum as well.

     

    Best wishes,

     

    Keith

  • Angela 746 posts since
    Jan 29, 2010
    Currently Being Moderated
    13. May 17, 2010 9:00 PM (in response to networkguy09)
    Re: frame-relay map ip command

    Hello,

     

      Now I see the source of your problem, global DLCI is totally and absolutely, extremely different from local DLCI.

     

      Using Keith's example from the video above (if he doesn't mind let me use it), R1 is connected to R2 and R3 using DLCI 102 and 103 respectively, while R2 and R3 connect back using 201 and 301, respectively.

     

      Now, this topology (local DLCI) is called point-to-point topology, because there is one-to-one correspondence. If you want to reach R2 from R1, use DLCI 201 -> 201, or vice versa on the way back.

     

      Another (local DLCI) topology is called multipoint. This time, R1 has only one PVC connect to it, let's called it 101 instead. Now, even though there are ACTUALLY 2 connections, R1 can only see one PVC, that means it must use that PVC for all connections, regardless it's going to R2 or R3 (meaning DLCI 101 -> 201 and DLCI 101 -> 301), always through PVC 101, but R2 and R3 retain their thought and still believe they can reach R1 using DLCI 201 (201 ->101) and 301 (301 -> 101), respectively. This is why it's called local DLCI, it changes only the local router's configuration. R2 and R3 doesn't really care what DLCI R1 is using.

     

      On the other hand, global DLCI is a completely different matter. Let's use the old example with R1, R2, and R3. R1, let's say, now have a global DLCI of 100, R2 has 200, and R3 is 300. What this means is that to reach R1 from R2, the path is DLCI 100 (R2 side) -> 200 (R1 side). The logic is TOTALLY the opposite of local DLCI!!! This also means for R3 to reach R1, it would take DLCI 100 (R3 side) -> 300 (R1 side).

     

      Make sure you REREAD the section, it's very confusing but fun. I believe WO has a note about the difference local and global DLCI are mapped. Oh, by the way, global DLCI is not really that common in the real world, but it might appear on the exam.

     

    Regards

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