frame-relay local-dlci question

[rcooke]

Hi guys this is my first time posting. I am taking the CCNA exam in a week and I am just rereading some books. The ICND chapter on frame relay says that you have to use the interface command "frame-relay local-dlci" when using point-to-point or multipoint with inARP. And dont have to use it with multipoint with no inARP. I sort of understand this. but the book never explained why. I can sort of understand why, but can someone please further explain why you have to use it in some cases and sometimes not. Thank You

 

[rcooke]

sorry i meant frame-relay interface-dlci. not frame-relay local-dlci

 

[csandu00]

(config-if)#frame-relay interface-dlci <dlci> associates a DLCI number with an interface (subinterface); this is used by InverseArp to dynamically map the dlci number to the IP address at the other end of the PVC. If this mapping is done manually, by issueing:
(config-if)#frame-relay map ip <ipaddress> <dlci>
the interface-dlci command is useless

Good luck! I'll follow you shortly. Come back and tell us how it was!

 

[rcooke]

that makes sense. so you only need to associate a subinterface with a dlci for layer 2 only communication (such as InARP)? let me see if i got it straight and anyone correct me if im wrong. you have to use frame-relay interface-dlci on a point-to-point connection because InARP is not used on point-to-point and no mapping is needed because any connection destined for that subnet has only one possible destination on the other side because it is point-to-point. mulitpoint with InARP needs frame-relay interface-dlci on subinterfaces to know what dlci to send a InARP packet. multipoint with static dlci mappings dont need frame-relay interface-dlci commands on the subinterfaces because as you mentioned earlier, they are useless with the mappings already. someone please let me know if im horribly wrong. also, does the router only use dlci's when needing to send a packet? or does it use them when recieving a packet to know which subinterface the packet should be received on? one more question, is an interface with no subinterfaces on it considered point-to-point or multipoint? thank you for all your help