Configuring Frame Relay subinterfaces

I've been working on configuring Frame Relay but some confusion has crept in. Can anyone spot the problem? The confusion is with assigning DLCIs to subinterfaces... one of my sources is telling me to configure the local DLCI and the other is telling me to configure the remote!

For example...

Router A
172.16.1.1/24
DLCI 102

Router B
172.16.1.2/24
DLCI 103

One source will tell you to assign the IP address and local DLCI together...

(R-A#ip address 172.16.1.1 255.255.255.0
(R-A#frame-relay interface-dlci 102

Then the other source will tell you to assign the IP address and the remote DLCI together...

(R-A#ip address 172.16.1.1 255.255.255.0
(R-A#frame-relay interface-dlci 103

Boson tell you to do the former, Cisco Press the latter. I don't believe either one has got it wrong, its more likely something I'm overlooking. I have tried mixing the different methods with no success.

Find more posts tagged with

SAVE $250 on Your CISCO Boot Camp — Use Code "EXAM26"

Exclusively for TechExams members for Infosec Boot Camps starting before April 30, 2026

View CISCO Boot Camps

Comments

dtlokee

You always assign the DLCI on the local side,not the remote. The DLCI is used by the frame switch to identify what PVC the frame belongs to. The IP address is the same as any IP address, it identifies the IP address of the local device, not the remote side.

totts

Thanks for clearing that up dtlokee and that's the method I've used with success. However, it still leaves my puzzled why in the cisco press book they configure the local IP interface with the remote DLCI (page 479, ICND).

Cucumber

You are talking about global DLCIs if I remember correctly. This is an idea that at first will drive you mad.

DLCIs have always always always local significance. That means you can have, say, DLCI number 7 at one location, and at another location another DLCI number 7, and so on:

Location1                                    Location2
  RouterA-----DLCI 7----FrameRelay----DLCI 7----RouterB

Now the Global DLCI idea stems from the need to match DLCI numbers to physical locations, to simulate the way a MAC address belongs to a single device. That way you can tell to which location a PVC connects to just by looking the at the DLCI number in the router's configuration.

Modifying the previous example, you can ask your FR provider to number the DLCIs according
to the location number.

Location1                                          Location2
  RouterA----DLCI 2----FrameRelay----DLCI 1-----RouterB

That way, when looking at RouterA´s configuration, you can tell that the PVC using DLCI number 2 will connect RouterA to Location2.

Finally, you can generate a diagram of your network using "global DLCIs" this way:

DLCI=1                                 DLCI=2
  RouterA------FrameRelay--------RouterB

This is just a way to put DLCI numbers on the diagram, although in real life each DLCI has local significance.

totts

Thanks for your very clear explanation Cucumber... you've obviously seen me struggling with this subject

I understand this concept now. I'd still like to know why the cisco press book assignes a local IP address to a remote DLCI whilst using the global addressing scheme.

My understanding of it now is that you're given a DLCI by the ISP (doesn't matter if its different or the same as all the rest on the network) and you assign your interface IP to it!

And yes you're right... its driven me mad

Netstudent

What section of what page of what book are you referring to? Maybe someone can skim through it and explain it to you. I would, but I don't have my CCNA books at work, just my NP book.

totts

Its in the 'Self-Study CCNA ICND Exam Certification Guide', page 479 and its Router 1s configuration.

datchcha

totts wrote:

Its in the 'Self-Study CCNA ICND Exam Certification Guide', page 479 and its Router 1s configuration.

Wow..what edition of the book, becuase the page you listed, is under the "Suggestion for Final Preparation" in my book.

source:
Odom, Wendell. CCNA Self Study CCNA ICND Exam Certification Guide. 9th printing. 2005. <ISBN 158720083X>

totts

r_durant

A bit late in bringing back up this one, but I'm now going through frame-relay...I think you may be referring to the "frame-relay map" command, which maps the local DLCI to the remote router's IP address...

It seems as though it depends on the situation...

I'm still trying to understand which configurations are used when....