I think I learned part of Frame Relay configuration incorrectly

CodeBlox

This little detail confuses me. When configuring a router to act as a Frame Relay switch, am I using local dlci's in the route statements or are they to be global dlci's?

What I'm asking may be more clear put this way: If I have three routers and a fr switch. Should I have three dlci's total or 6 total if this were a full mesh topology and not point to point or point to multipoint

CodeBlox

And to be even more clear, would a frame relay switches "show frame-relay route" command look somethings like THIS for a three router topology:

R4(config-if)#do show fram route
Input Intf      Input Dlci      Output Intf     Output Dlci     Status
Serial0/1       122             Serial0/2       221             active
Serial0/1       123             Serial0/3       321             active
Serial0/2       221             Serial0/1       122             active
Serial0/2       223             Serial0/3       322             active
Serial0/3       321             Serial0/1       123             active
Serial0/3       322             Serial0/2       223             active

or this

R4(config-if)#do show fram route
Input Intf      Input Dlci      Output Intf     Output Dlci     Status
Serial0/1       200             Serial0/2       100             active
Serial0/1       300             Serial0/3       100             active
Serial0/2       100             Serial0/1       200             active
Serial0/2       300             Serial0/3       200             active
Serial0/3       100             Serial0/1       300             active
Serial0/3       200             Serial0/2       300             active

DO know that I tried both ways and they bold yield active PVC's and all interface are pingable on both. So which is "correct"?

tomaifauchai

I think this will answer all your questions related to Frame-relay switching

Frame Relay Switch Configuration For Cisco Lab

Forsaken_GA

CodeBlox wrote: »

What I'm asking may be more clear put this way: If I have three routers and a fr switch. Should I have three dlci's total or 6 total if this were a full mesh topology and not point to point or point to multipoint

You'll have 2 DLCI's per router, ie

R1: 12,13 (i choose my dlci's to give me an idea of connection, 12 in my mind stands for 'router 1 to router 2'. 13, R1 to R3, and so on)
R2: 21,23
R3: 31,32

DLCI's are locally significant, they represent a connection to a remote point, and in one direction.

Jeremy Ciora explained it best, I think. DLCI's are like the gates at the airport. Let's say you fly from Atlanta to London. And in Atlanta, your flight leaves from gate A1. When you get off the plane, if you turn around and look at the gate number after you exit, unless it's some freak occurrence, it's not going to be A1. So your flight (traffic) leaves from one gate (DLCI) and when you return, you take a different gate (DLCI) to get back home.

Forsaken_GA

CodeBlox wrote: »

And to be even more clear, would a frame relay switches "show frame-relay route" command look somethings like THIS for a three router topology:

R4(config-if)#do show fram route
Input Intf      Input Dlci      Output Intf     Output Dlci     Status
Serial0/1       122             Serial0/2       221             active
Serial0/1       123             Serial0/3       321             active
Serial0/2       221             Serial0/1       122             active
Serial0/2       223             Serial0/3       322             active
Serial0/3       321             Serial0/1       123             active
Serial0/3       322             Serial0/2       223             active

or this

R4(config-if)#do show fram route
Input Intf      Input Dlci      Output Intf     Output Dlci     Status
Serial0/1       200             Serial0/2       100             active
Serial0/1       300             Serial0/3       100             active
Serial0/2       100             Serial0/1       200             active
Serial0/2       300             Serial0/3       200             active
Serial0/3       100             Serial0/1       300             active
Serial0/3       200             Serial0/2       300             active

DO know that I tried both ways and they bold yield active PVC's and all interface are pingable on both. So which is "correct"?

They're both correct. As I said, DLCI's are only locally significant. It's a data construct that says I want to map this connection to this IP address going out this interface. There's not any actual overlap if you do it the second way, but it will drive you bonkers if you address it like that.

CodeBlox

I think I get it now! Looking back at that chapter, (wendell Odoms book) for some reason I think it didn't do a good job explaining this at all! I think I learned more from researching on the internet and asking here after all of this confusion with global/local dlci's and whatnot. I can see what you mean about the second frame relay route output.

Another thing, does frame relay encapsulation cause the router to send EVERY THING into the "cloud"? I ask this because I have to add map statements (no using inverse-arp) just to ping the local serial interface on a specific router.

CodeBlox

Bump...

Forsaken_GA

CodeBlox wrote: »

I think I get it now! Looking back at that chapter, (wendell Odoms book) for some reason I think it didn't do a good job explaining this at all! I think I learned more from researching on the internet and asking here after all of this confusion with global/local dlci's and whatnot. I can see what you mean about the second frame relay route output.

Another thing, does frame relay encapsulation cause the router to send EVERY THING into the "cloud"? I ask this because I have to add map statements (no using inverse-arp) just to ping the local serial interface on a specific router.

This is because the local router has no layer 2 to layer 3 mapping for it's own interfaces. One of the big pains in the ass with serial interfaces. So for a ping to succeed, it has to send it out, and the remote router says 'hey, i know where this packet goes!' and sends it back to you. When your side strips off the layer 2 on the return packet, and looks at the layer 3 packet, it sees it's for itself. So it returns an ICMP echo reply out the same DLCI to the remote router, who then sends it back, because it has a mapping for you. Then once again it dencapsulates it, looks at the layer 3 echo reply, and then reports it as normal.

Basically, it has to be sent via a path that has a DLCI that can identify it, and that means a remote router, since DLCI's map to remote.

It's arcane crap like this that makes frame relay such a damn pain to work with.

CodeBlox

Great explanation. Although I would think that since the router would check(figuratively) the routing table, it would see that address as a part of a directly connected network. Does make sense though.