Setting up a lab for frame relay?

One of your routers is emulating a frame relay switch i.e. a frame realy cloud. The other is acting as a router configured with frame relay. As such it is correct to have the same dlci on both devices. \\ \\

A better way is to configure a router with serveral serial ports as a frame relay switch. Then connect two or three routers to the frame relay switch and configure them for frame relay.

Here is a configuration for the router to be configured as a frame relay switch:

Here is an article that explains the dlci question you are asking. It is a point of confusion. This guy expalins it best.

Search for Frame Relay

Then look for How come my circuit doesn't come up?

It is a great article.

Good luck

I hear you - I do!

Wendell Odom clearly knows what he's saying, but often leaves much to be desired.

Luckily, I purchased The Bryant Advantage before I'd purchased any offical Cisco media, so my understanding of Frame Relay had already been given a great boost.

If you want to purchase some of his study material, like "The Ultimate CCNA package", then go to

I'd set up a FR lab at home, with three FR routers running PVCs through my Frame Relay Switch (all thanks to a link on Chris Bryant's website, and no thanks to Wendell Odom (bless him)).

Good luck, Regards, Jason Tomasi

Jas> I'm trying to understand frame relay but finding some of the examples

Intuitive wrote in news:foumfd$j0f$ snipped-for-privacy@lust.ihug.co.nz:

I have the feeling the books were rushed out as there are quite a few spelling mistakes & in one part an incorrect diagram appears, totally unrelated to the text, maybe the next editions will be better? I'll have to go on the the Cisco Press site & download the addendum.

Frame relay is usually represented as a cloud, with only the border routers drawn. What's actually inside the cloud is nothing more that a frame relay switch (or more than one, but this does not change the concepts), that is, another router which acts as a switching point between the border routers, and through which all the virtual circuit pass.

The base rule about DLCIs is that they are locally significant. This means that DLCI, say, 100 on router R1 has nothing to do with DLCI 100 on router R2, if R1 and R2 are border routers (ie, neither is a FR switch). Another way to look at it is that each DLCI is significant only between the router and its attached switch, and does not extend from end to end (as you will see).

How comes then that Odom says that DLCIs can also be used with "global" significance? Well, if you understand how a FR switch works then you'll see that what he describes is actually possible, without contradicting the local significance rule.

Take the following (a bit simplified) FR hub-and-spoke topology as an example:

S2 S3 \\ / \\ / \\ / \\ / \\/ HUB1-----------S4

This is what you see in CCNA books, with the links plunged into "the cloud". But of course, all the routers (HUB1, S2, S3, S4) are connected to a FR switch. So, the actual topology is as follows:

S2 S3 \\ / \\ / \\ / \\ / \\ / FRSW----------S4 | | | | HUB1

Here we see that the switch is just another router, with four serial interfaces, using frame relay encapsulation (let's assume that HUB1, S2, S3 and S4 are connected to FRSW's port s1, s2, s3 and s4 respectively).

Being an hub-and-spoke topology, each spoke has a VC to the hub, and the hub has three VCs, one to each spoke (if we want a full mesh the concepts are exactly the same, it's just a matter of adding few config lines to each router, as you'll see). It's the switch's job to set up all these VCs.

Now, let's revisit the concepts of local and "global" DLCIs using the complete picture (ie, with the switch).

With local DLCIs, they say, /the hub is known by each spoke through a different DLCI, and, generalizing (if a full mesh is in effect), router Rx is known by router Ry and Rz through different DLCIs/. Thus:

S2 S3 \\201 /301 \\ / \\ / \\ / \\ / FRSW----------S4 | 401 | | |102,103,104 HUB1

Near each router are the DLCIs that depart from it. That is, S2 uses DLCI

201 to talk with HUB1, whereas S3 uses DLCI 301 to talk with HUB1, and so on. All FRSW has to do is to change DLCIs in frames that pass through it, and route them out the correct port. For example, if S2 is talking with HUB1, FRSW will receive a FR frame on port 2, with a DLCI of 201. Since FRSW knows (from previous configuration) that there is a VC connecting its port 2 and 1, with an incoming DLCI of 201 and on outgoing DLCI of 102, it will just rewrite the DLCI in the frame (putting 102) and send it out port

1. If HUB1 talks to S2, the process will just be reversed (from port 1, DLCI 102, to port 2, DLCI 201).

So, an example configuration for the routers would be:

S2# int s0/0.201 point-to-point frame-relay interface-dlci 201

S3# int s0/0.301 point-to-point frame-relay interface-dlci 301

S4# int s0/0.401 point-to-point frame-relay interface-dlci 401

HUB1# int s0/0.102 point-to-point frame-relay interface-dlci 102 int s0/0.103 point-to-point frame-relay interface-dlci 103 int s0/0.104 point-to-point frame-relay interface-dlci 104

And, on the switch:

FRSW# frame-relay switching

int s2 frame-relay route 201 interface s1 102

int s3 frame-relay route 301 interface s1 103

int s4 frame-relay route 401 interface s1 104

int s1 frame-relay route 102 interface s2 201 frame-relay route 103 interface s3 301 frame-relay route 104 interface s4 401

Essentially, the switch is told how to rewrite DLCIs and route frames depending on incoming interface and incoming DLCI.

Now, let's see how we might configure "global" DLCIs. For global DLCIs, CCNA books usually have a picture similar to this:

S2 S3 \\202 /303 \\ / \\ / \\ / \\ / HUB1----------S4 101 404 Now, each router has its own (globally unique) DLCI. Let's start by redrawing the picture using the actual topology with the switch: S2 S3 \\202 /303 \\ / \\ / \\ / \\ / FRSW----------S4 | 404 | | |101 HUB1

With the above notions, and knowing how the switch FRSW works, it's now just as easy to configure the routers:

S2# int s0/0.101 point-to-point frame-relay interface-dlci 101

S3# int s0/0.101 point-to-point frame-relay interface-dlci 101

S4# int s0/0.101 point-to-point frame-relay interface-dlci 101

HUB1# int s0/0.202 point-to-point frame-relay interface-dlci 202 int s0/0.303 point-to-point frame-relay interface-dlci 303 int s0/0.404 point-to-point frame-relay interface-dlci 404

And, on the switch:

FRSW# frame-relay switching

int s2 frame-relay route 101 interface s1 202

int s3 frame-relay route 101 interface s1 303

int s4 frame-relay route 101 interface s1 404

int s1 frame-relay route 202 interface s2 101 frame-relay route 303 interface s3 101 frame-relay route 404 interface s4 101

Now, read the above configs carefully. Where's the difference? The difference is that, with different (and more clever) DLCIs assignments, each router has only a single DLCI and is identified with that one DLCI to all the other routers. The only difference is in how DLCIs are chosen (and the different configs that follow). Whereas before each router was thinking in terms of "source" DLCIs, now each router must think in terms of "destination" DLCIs. As you will realize if you think about it for a moment, this is just a "mental" (or conceptual) difference, since the actual logic used by the routers is exactly the same (since the DLCIs assigned to each VC are still unique, each router has no choice but to use that DLCI). The difference is that, before, a router was sending packets on a particular VC using a "source" DLCI, whereas now each router send packets on a particular VC using a "destination" DLCI. As I said before, this is only a conceptual difference, since the routers are not aware in any way of the meaning of the DLCI they are using; they just use it. It's the way DLCI are assigned (by humans :-)) that makes them "source" or "destination", "local" or "global". But, from the network's perspective, the whole system works *exactly* the same in both cases, and, in particular, DLCI are still "locally" significant (ie, only between each router and the switch).

I perfectly know that I did not directly answer your original question, but I hope that the above will help you set up a FR lab with more awareness of what goes on behind the scenes. You were trying to use only two routers and the lab was (sort of) working, but, as you hopefully know by now, to set up a proper FR lab you'll need at least THREE routers (one being the switch).

Regards

pk wrote in news:fovgao$ukr$ snipped-for-privacy@aioe.org:

Many thanks for the very detailed answer, I do now understand the concept of global DLCIs and how the assignment (& consequent configuration) can make a more understandable schema. I have managed to also configure my 3 routers correctly to replicate frame relay but I am far from 100% on the configuration & it took me quite a while to figure everything out correctly. I suppose this is why the CCNA is such a valuable qualification to have.

Jase