Frame relay map command

[lupidus]

I was going over some sample problems for the BCRAN exam and came across one that confused me.

You are troubleshooting a connectivity problem on R2.

R2-(a)-----------(b)-R1-(c)-------------(d)-R3

a: S0 10.1.1.2 DLCI 100
b: DLCI 300
c: S0 10.1.1.1 DLCI 400
d: S0 10.1.1.3 DLCI 200

You can ping R1 from R2, but can't ping R3 from R2. What is the correct set of frame-relay map commands on R2 to fix this problem?

Since you are always supposed to use the local DLCI with the frame-rel map command, I would say the correct answer is:

frame-relay map ip 10.1.1.3 100
frame-relay map ip 10.1.1.1 100

However, since we are going through R1, from R1's perspective, we should also be referencing its DLCI? So should the answer be the following, instead?

frame-relay map ip 10.1.1.3 100
frame-relay map ip 10.1.1.1 400

Thanks for any help. I hope the above diagram is clear enough to show whats going on here.

/Tristan

 

[Jsteve]

I believe this is a basic multipoint hub and spoke config, R1=hub and R2 & R3=spokes,.

R2
frame-relay map ip 10.1.1.1 100 (broadcast)

R1
frame-relay map ip 10.1.1.2 300 (broadcast)
frame-relay map ip 10.1.1.3 400 (broadcast)

R3
frame-relay map ip 10.1.1.1 200 (broadcast)

the basic thing to remember when doing the map statements is the you use the destination router address your trying to reach and your dlci number.

 

[Microbyte]

but isn't it the way the question is setup, frame-relay mapping only concerns with R2?

R2
frame-relay map ip 10.1.1.1 100 (broadcast)

is correct. but i think, lupidus is asking for additional static frame-relay mapping command line from router 2. if i'm understanding correctly.

Microbyte

 

[Jsteve]

but isn't it the way the question is setup, frame-relay mapping only concerns with R2?

That’s what it looks like, but I thought of I gave him a complete perspective, he would understand it better and would be able to see where each mapped dlci is used.

I not sure either what he is actually asking, lupidus let us know if this clarifies your things for you? If not please rephrase the question.

 

[techkiwi]

Jsteve and Microbyte, I think your answers are pretty much on the button, but I would raise this point.

I think with the command frame-relay map ip 10.1.1.1 100 broadcast you're setting up a valid map from R2 to R1 but then it will only get through to R3 if you're running a dynamic routing protocol or have some form of static map pointing to R3. Otherwise you'll have to put in an additional command on R2 frame-relay map ip 10.1.1.3 100. Or does it not matter because the two interfaces on R1 are both in the same subnet?

Graham

 

[Jsteve]

you are correct as far as the Dyn routing protocol setup.

It can be done as you suggested by mapping the 1.3 100, but you are than setting up a fully mesh network and paying for another PVC curcuit ($$$). directly connecting R2<->r3.

 

[techkiwi]

Ah, I see.