Frame-Relay subject matter contradiction in CCNA...

Unanswered Question
Jul 14th, 2007

Hi all,

Almost at the end of my CCNA preparation (using 2 books, Sybex & cisco press); when I am totally flabbergasted on the frame-relay chapter in the books!

Todd's book says DLCIs are locally significant & config must include local DLCI. e.g. # frame-relay interface-dlci 101.

Cisco press says DLCIs are globally significant & config must include remote net DLCI. e.g. # frame-relay interface-dlci 550.

What is going on?

Then, you can configure frame-relay:-

1] Without using sub-interfaces (e.g. 3 routers using 1 subnet without using p-to-p or p-to-mp).

2] Using point-to-point sub-int.

3] using point-to-multipoint.

4] Hybrid - mix of p-to-p & p-to-mp.

The content (only FR) in both the books 'just' presents the information 'about' frame-relay. They do not tell you as a customer or test-taker that given a scenario, how 'should' you do it & why; given so many options?

For the exam, what is the criteria by which I decide what config to use. And from the exam point of view, is there a 'right cisco way' to do it?

Also, could anyone please mention any links on good explanations with configs on FR. I really would appreciate that.

Thanks

Glen

I have this problem too.
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jasonnzcisco Sat, 07/14/2007 - 21:51

Hello Glen,

Your question is fairly comprehensive but I'll try and answer it for you.

I have taken the test twice now and on the second time past so my knowledge of the exam is this.

The most important things you need to know are these,

DLCI's are Layer 2 that is the data-link layer.

IARP is used to translate from DLCI to IARP (Inverse Arp).

And the DLCI is also only significant from your frame-relay Router to the Telco's Switch and not to your other Router on the WAN. You must remember this. The Telco will provide the other DLCI to your other Router.

Point to point breaks the splint horizon rule, multi-point gets around this. REMEMBER this and you should be fine, seriously.

Post a comment if you require further explanation.

Regards J

glengregory Sun, 07/15/2007 - 20:14

Thanks for your reply!

I already know what you have just mentioned. That's not my question.

2 books giving exactly the opposite config; which one is right?

If I have to configue 3 Routers connected to FR and the ISP gives me this:-

R1 DLCI = 100

R2 " = 200

R3 " = 300

what will be the config on all 3 w.r.t. the command # frame-relay interface-dlci; for the exam? If you have both the books, take a quick look and you'll see what I mean.

Meanwhile, I tried checking on Cisco docs and found configs to be local (like in Todd's book). It did'nt satisfy me. I'll search again.

I really need to get through this as I feel I am stuck here. I have only 1 chap (ACL) to go before I am finally prepared for the exam & real world.

Thanks again

Glen

darylbybee Mon, 07/16/2007 - 18:08

I am also doing my final prep for the CCNA and I hope this answers your question.

Global addressing is simply a way of choosing DLCI numbers when planning a FRAME Relay network. For example the service provider hands out a planning spreadsheet

Router A is DLCI 40

Router B is DLCI 41

Router C is DLCI 42

Router A uses DLCI 41 when sending a frame to router B and DLCI 42 when sending to router C

Router B will recieve the frame with DLCI value 40 as will Router C recieve the frame with DLCI value 40

Local addressing is a fact, global addressing does not change these rules. Global addressing just uses the planning with the service provider to make DLCI assignment more obvious.

Daryl

glengregory Wed, 07/18/2007 - 23:19

And it also tells you about GLOBAL. Infact, if you read ICND book, all configs are for global DLCIs.

It looks like NOBODY can answer this question for sure.

For my part, I searched in Cisco Docs & docs CD and found some docs (quite old pre 12.1) describing FR. They ALL talk about local DLCI when configuring.

In a desperate last attempt, I found some free info on How2pass.com. There, all configs are for local only & the explanation is very good. With no other choice, I am going to take this info as the final word on FR.

If anyone's out there with the answer w.r.t. the exam, I would really appreciate your input.

Thanks

Glen

mohammedmahmoud Thu, 07/19/2007 - 12:11

Hi Glen,

If you search cisco docs, i'll guess that you'll find this statement: "In the basic Frame Relay specification, DLCIs are locally significant (connected devices might use different values to specify the same connection). In the LMI extended specification, DLCIs are globally significant (DLCIs specify individual end devices)."

As for the exam context DLCI is considered to be local significant (significant only between the router and the FR switch in front of it).

Good luck in your exam :)

HTH,

Mohammed Mahmoud.

fredhomeville1 Thu, 07/19/2007 - 11:33

Hi, I am also taking my ccna next week. look for some info on LMI. It helps with understanding the local and global significance of the dlci.

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