FRAME RELAY design question

Answered Question
Jul 30th, 2009

Hi !

I'm currently studding BSCI Exam, I setup a small frame relay lab with 4 routers where one of them is setup as a frame relay switch.

In all lab setup I seen about frame relay I find different DLCI number on all interfaces. I know DLCI is locally significant on the router with frame relay switch. But to make easier to understand why we don't use same DLCI number when I setting up PVC between to router ? I had tested it and it is working properly I can use DLCI #202 on 2 differents interfaces of my frame relay switch which are locally significant with there connected router....

interface Serial1

description FR to East

no ip address

encapsulation frame-relay

clock rate 64000

frame-relay lmi-type cisco

frame-relay intf-type dce

frame-relay route 201 interface Serial0 102

frame-relay route 202 interface Serial2 202

!

interface Serial2

description FR to West

no ip address

encapsulation frame-relay

clock rate 64000

frame-relay lmi-type cisco

frame-relay intf-type dce

frame-relay route 202 interface Serial1 202

frame-relay route 301 interface Serial0 103

and on thoses 2 remotes routers I used DLCI #202 on both to map my connection.

Is it only for understanding and make sure no confusing about the understanding the DLCI is always locally significant between frame-relay interface and it's directly connected router ?

Thanks a lot for your reply !

I have this problem too.
0 votes
Correct Answer by Giuseppe Larosa about 7 years 4 months ago

Hello Christian,

your understanding is correct DLCI is locally significant on a single link.

There has been and it is in use a convention called global addressing used by FR service providers that used this idea:

pretending that DLCI are like MAC addresses from every other site / FR DTE router you used the same DLCI to reach the same remote site x.

The network arranged DLCIs so that the customer could think of them as addresses.

But this is just a convention: reality is that you need to use the locally significant DLCI to reach the remote site not that the remote is addressable by a specific DLCI value.

Inside the FR network the DLCI changes at each FR switch hop but this is transparent to users.

The same happens for ATM vpi/vci

Hope to help

Giuseppe

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Correct Answer
Giuseppe Larosa Thu, 07/30/2009 - 11:25

Hello Christian,

your understanding is correct DLCI is locally significant on a single link.

There has been and it is in use a convention called global addressing used by FR service providers that used this idea:

pretending that DLCI are like MAC addresses from every other site / FR DTE router you used the same DLCI to reach the same remote site x.

The network arranged DLCIs so that the customer could think of them as addresses.

But this is just a convention: reality is that you need to use the locally significant DLCI to reach the remote site not that the remote is addressable by a specific DLCI value.

Inside the FR network the DLCI changes at each FR switch hop but this is transparent to users.

The same happens for ATM vpi/vci

Hope to help

Giuseppe

Peter Paluch Thu, 07/30/2009 - 13:27

Giuseppe,

I am very happy that you brought the issue of Global DLCIs to the sunlight. I would like to ask you something regarding that.

I understand the logic behind Global DLCIs and their usage intention. However, there are several documents discussing the LMI in which the global addressing was allegedly an LMI extension! For example, from the Cisco's Internetworking Technology Handbook at

http://www.cisco.com/en/US/docs/internetworking/technology/handbook/Frame-Relay.html#wp1020640

The Local Management Interface (LMI) is a set of enhancements to the basic Frame Relay specification. The LMI was developed in 1990 by Cisco Systems, StrataCom, Northern Telecom, and Digital Equipment Corporation. It offers a number of features (called extensions) for managing complex internetworks. Key Frame Relay LMI extensions include global addressing, virtual circuit status messages, and multicasting.

Now, as the global addressing is really a convention of using DLCIs in a network, nothing more, what extension is that document really talking about? Can you perhaps enlighten me on this?

Best regards,

Peter

Giuseppe Larosa Thu, 07/30/2009 - 23:05

Hello Peter,

there is an Enhanced LMI (that should be Cisco proprietary) described here

http://www.cisco.com/en/US/partner/docs/ios/wan/configuration/guide/wan_cfg_frm_rly_ps6350_TSD_Products_Configuration_Guide_Chapter.html#wp1051404

About the document that you have linked it is usually a good reference.

To try to answer to your question I would go to standards organizations

FR forum has become the broadband forum.

I think we should look here

http://broadband-forum.org/technical/frametechspec.php

more specifically the first document.

appendix B talks of extensions to original Q.933 standard definition.

But these are more near to ELMI concept because they add the capability to transfer configuration information at the UNI interface via LMI messages.

I still keep my idea that Global addressing is just a convention.

Some efforts can have been done in helping the provision of Global Addressing DLCIs but I'm not aware of this.

Hope to help

Giuseppe

Peter Paluch Thu, 07/30/2009 - 23:48

Giuseppe,

Thank you for your answer. I see the issue the same as you - the global addressing is only a particular system to assign DLCIs. It will already work with the present LMI without any additions. What possible function could be added to the LMI, then?

Best regards,

Peter

jimmysands73_2 Thu, 07/30/2009 - 21:15

Aucune,

Are you doing these out of the BSCI Lab Portfolio? Just curious, I started this book about a month ago, but I got a full time job, so time has been limited.

xine xine Fri, 07/31/2009 - 11:29

Hi Jimmy,

what are you talking about ?? "BSCI Lab Portfolio", for me studdy I had buy CCNP Official Certification Guide Package. But for the BSCI, I find the hard to follow and to read, also the errata is a little bit big (10 pages around) which also contain errors (typing error which can become confuse EIGRP/IGRP).... I really not recommand this book for some one else... and some other ressources like Internet and this forum news group.

Also I by some old Cisco Router on E-BAY on at reseller in Montreal who sell used electronic material... (He have a lot of Cisco stuff but form other compagny also and some stuff are not computer related, like professionnal television camera)

Let me know if this question did not answer to your question....

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