Frame-Relay Incoming DLCI

Is there a way to tell what DLCI another device will send to you without accessing the other devices config?


  • On ingress/inbound Frame-Relay frames, the DLCI in the F-R header has nothing to do with the DLCI that the remote device originally applied when transmitting the frame.  The DLCI assigned to that PVC is only locally-significant between you and your local Frame-Relay switch.

    So what you need to ask yourself is, "What DLCI value would my router apply if it were to TRANSMIT a frame to that remote destination?"  Whatever your answer is to that question, that same DLCI value will be seen in frames that you receive FROM that destination.


    Here's an analogy,

    Imagine that you are located in Boston, MA and standing in front of a tunnel.  There is a sign at the top of that tunnel (the DLCI value) that reads, "Tunnel-1".  You know that if you enter that tunnel, you will pop-out in Boise, Idaho. When someone is standing in Boise looking at that tunnel (leading back to you, in Boston) it may say, "Tunnel-1"...or it might say, "Tunnel-87".  But it doesn't really matter what THEY see the as the name.  That tunnel only goes to one Boston.  So if you are standing in Boston, looking at that tunnel, everything that comes goest into, or comes out of that tunnel (from your perspective) is related to "Tunnel-1"...regardless of what the sign may have been on the other end of that tunnel when they first entered it.

    Hope that helped!

  • Thanks Keith. I realize that a DLCI is only locally significant. I guess I worded my question wrong. I was wondering if there was a way to see what DLCI is assigned to MY IP on a neighboring router without actually accessing that router.

  • Without accessing the remote router?  Nope...there's no way to do that unless you call up your WAN provider and ask them.

  • That's what I figured, but I wanted to check. Thanks for the response!

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