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ryan80

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frame relay question for learning DLCIs

I am studying for my CCNA and have a few questions regarding frame relay DLCI's. I am trying to understand how they work on a router and what they refer to.

For an example we have the following setup:


R1---------Frame Relay Switch--------------R2


Now on R1 I use the commands for a point-to-point connection

ip address 192.168.1.1 255.255.255.0
frame-relay interface-dlci 100

On R2 i use

ip address 192.168.1.2 255.255.255.0
frame-relay interface-dlci 200

First thing that I need to be sure about, is that there is only one PVC in this example. It is my understanting that a PVC refers to a router to router connection, in this example from R1 to R2. Is this correct?

Secondly am I correct in saying that the DLCI refers to section of the PVC between the router and the frame relay switch?

Lastly when you configure the command "frame-relay interface-dlci 100" on R1, the DLCI 100 is refering to the link between itself (R1) and the frame relay switch. It is then the frame relay switch's job to pass the frame received from R1 along the DLCI 200, then reaching R2 (after switching the DLCI identifier). Does this sound correct?


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moon_blue69

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Avatar of ryan80
ryan80

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Thanks donjohnston.

Thank for letting me know that you dont need to specify the dlci if there are no subinterfaces.

I am pretty sure that I understand the theory now.

Looking at it in a layman's view, a PVC seems like it consists of 2 DLCI's in my simple configuration. The first DLCI refers to the connection between R1 and the Frame Relay switch and the second DLCI refers to the connection between the Frame Relay Switch and R2.
> The first DLCI refers to the connection between R1 and the Frame Relay  switch and the second DLCI refers to the connection between the Frame  Relay Switch and R2.

This is a problematic description. In many situations, a router may have access to multiple PVC using multiple DLCIs. Which means a connection between R1 and the Frame-Relay edge switch could be referred to by multiple DLCIs.

So a better approach would be to consider the DLCI as a means to utilize a specific PVC.
Avatar of ryan80

ASKER

Yeah, i guess that i didnt word it the best, but I understand exactly what you are saying thank you for the help and answering my questions.
Don't sweat it. Frame-Relay is really an antiquated technology. Sadly, you really only need to know for CCNA and for the routing protocols section of the CCNP.