Confused about frame-relay mappings (Theory question)

[player9]

Hi all,

please help me understand the following...

I'm kinda confused about the difference between frame-relay mappings (frame-relay map ip) and the frame-relay interface DLCI associations. On on top of that we also have frame-relay route.

So far here's my understanding... please correct me if I'm wrong:

When we have multipoint interfaces (same subnet) and we don't have full mesh OR when we don't have inverse arp we need frame-relay mappings.

When we have full mesh and inverse arp we don't need mappings but we need the frame-relay interface DLCI  (dlci association)

When we have point to point interfaces (different subnets between subifs) we don't need mappings either but we do need interface DLCI associations.

Now finally, when we do frame-relay switching we ONLY need frame-relay route commands and don't need frame-relay interface DLCI nor frame relay mappings (as we don't have ip addresses anyhow)

So I think I got it all.. still, I'm not 100% clear on the frame-relay interface DLCI command. Is there any time where we need that AND the mappings under an interface/subif? I've never done a lab where I had to add both under an interface, always one or the other..

thank you,

[Richard Burts]

I will start with the one where I think you have it (mostly) correct:

You only need frame-relay route when you are doing frame relay switching. (But you also need frame relay dlci when you are frame relay switching.

I would suggest that you always need frame relay DLCI when you are doing frame relay. Sometimes you need to explicitly configure the DLCI and sometimes the IOS will figure it out and do it automatically. But you can not process frame relay without having DLCI on the interfaces.

And I would suggest that if you are doing only frame relay switching you do not need frame relay mapping. But if you are configuring router interfaces for connection as frame relay end devices then you always need frame relay mapping. Sometimes you must explicitly configure the mapping and sometimes the router will figure it out dynamically and configure it (most especially for point to point subinterfaces the mapping is automatically and dynamically set up).

HTH

Rick

[player9]

Hi Richard,

thank you for the reply! Let me give you an example here's a config from the cisco net academy on using a router as a frame relay switch:

interface Serial1/0
 no ip address
 encapsulation frame-relay
 serial restart-delay 0
 clock rate 128000
 frame-relay intf-type dce
 frame-relay route 102 interface Serial1/1 201
 frame-relay route 103 interface Serial1/2 301
interface Serial1/1
 no ip address
 encapsulation frame-relay
 serial restart-delay 0
 clock rate 128000
 frame-relay intf-type dce
 frame-relay route 201 interface Serial1/0 102
interface Serial1/2
 no ip address
 encapsulation frame-relay
 serial restart-delay 0
 clock rate 128000
 frame-relay intf-type dce
 frame-relay route 301 interface Serial1/0 103
interface Serial1/3

at no point do we have any frame-relay interface dlci commands.

Also for point-to-point interfaces we have interface dlci commands but no mapping commands.

And also for multipoint subifs we have frame-relay map ip commands but no frame-relay interface dlci commands.

[cadet alain]

Hi,

You don't need frame-relay interface-dlci command on a frame-relay switch, it won't route the packets but switch the frames

between interfaces.

your summary was as far as i know correct and indeed we could have a frame-relay interface-dlci and frame-relay map

command under the same multipoint interface if we were doing stuffs like frame-relay end-to-end keepalive(FREEK)  or frame-relay traffic shaping(FRTS) or PPPoFR but these are definitely not CCNA or CCNP topics so i would always consider

that both won't be configured at the same time for exam purposes.

Regards

Alain

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