Frame Relay = Huh?

veritas_libertas

I've been trying to wrap my head around Frame Relay now for a couple of days. I've looked at Chris Bryant's material and Todd Lammle's chapter on it. It may just be me, but I feel like they are both breezing over it and I'm left scratching my head. Does the CCNA only require a light understanding? Is that why I feel like they are not digging into the the meat of the material?

I have a couple of questions that I'm not sure were explained in any material I've read, at least not that I could find.

• LMI, does it need to be configured on every DCE and DTE? I understand that it's the "heartbeat," for a Frame-Relay network, but I wasn't sure if it only had to be configured on one end or not.

• DLCIs, I still don't get what they are for. I realize they are only locally significant, but are they like a static route?

• Local vs Global DLCI? Good grief this is confusing. Is it relevant to only a circuit, or only to the router's mapping?

I have to say that Frame Relay is one of the only chapters that has made me want to set my INCD2 book on fire

Does anyone know of a lab for Frame Relay that really walks you through this material to give you a better idea of what you really need to know about Frame Relay? I'm going to do the labs from Free CCNA Workbook. I'm hoping they will clear some things up for me.

NetworkVeteran

veritas_libertas wrote: »

Does the CCNA only require a light understanding? Is that why I feel like they are not digging into the the meat of the material?

Yeppers. Years ago, frame-relay was covered in-depth by the CCNP. What's more important to a modern CCNA/CCNP is not how frame-relay works, but rather how routing functions on top of it.

LMI, does it need to be configured on every DCE and DTE? I understand that it's the "heartbeat," for a Frame-Relay network, but I wasn't sure if it only had to be configured on one end or not.

The LMI-type is auto-sensed in modern IOS images. Therefore, no LMI configuration is necessary.

DLCIs, I still don't get what they are for. I realize they are only locally significant, but are they like a static route?

Suppose you have three routers: R1(NYC), R2(Miami), and R3(LA).

The R1 router may have one physical cable to his carrier. However, that one cable will contain two "Virtual Circuits". One connects to R2. The other connects to R3. Each VC has an ID a.k.a a DLCI#.

Local vs Global DLCI? Good grief this is confusing. Is it relevant to only a circuit, or only to the router's mapping?

A DLCI# is typically locally significant. A local DLCI scheme may look like this--

R1-to-R2: 102
R1-to-R3: 103
R2-to-R1: 201
R2-to-R3: 203
R3-to-R1: 301
R3-to-R2: 302

When R1 wants to reach R2, he sends a frame with DLCI #102. Notice, that R1 & R2 both use different DLCI#'s to reach R3. This is unlike IP where R3 would be identified by a single IP address. This is why we say DLCI#'s are locally significant. A global DLCI scheme, on the other hand, looks like this:

R1: 100
R2: 200
R3: 300

Any device that wants to talk to R3 will use VC# 300. This is rarely implemented. Focus on Local DLCIs.

veritas_libertas

Thanks. I was hoping it wasn't just me, and they were in fact skimming only the surface. I'm going to be very amused if I get the CCNA done this year, and next year Frame Relay is removed from it

Thanks for your help. You helped make the glass a little clearer for me to see through.