DLCI Question

waru

Hi

I am having a few probs getting my head around DLCI’s. I know they are loacally significant but I thought that an individual DLCI was allocated to each sub-interface/PVC and then ip addresses that can be reached via that PVC are mapped to that DLCI


This is a frame relay config from Todd Lamle’s CCNA book, what I don’t understand is why he is using 3 DLCI’s on one subinterface/PVC. Also where would the frame-relay interface-dlci command be used?


RouterA(config)#int s0
RouterA(config-if)#encap frame
RouterA(config-if)#int s0.16 point-to-point
RouterA(config-if)#no inverse-arp
RouterA(config-if)#ip address 172.16.30.1 255.255.255.0
RouterA(config-if)#frame-relay map ip 172.16.30.17 16 ietf
broadcast
RouterA(config-if)#frame-relay map ip 172.16.30.18 17
broadcast
RouterA(config-if)#frame-relay map ip 172.16.30.19 18

Cheers!
Waru

EdTheLad

Are you sure thats in the CCNA book? as its not correct, above should be a multipoint interface not a ptp.On a ptp interface there is only one endpoint so therefore there is only one remote ip address on the segment.
The above config is used for a multipoint interface, its basically trying to represent a broadcast network over a FR cloud.Ethernet is a broadcast network which means on the same lan segment you can have multiple transmitters and receivers on the same subnet.In multipoint FR its trying to emulate the same behavior , all the remote devices
must share the same ip subnet.
The mapping statement is used to tell the router which dlci to use to talk to which remote device, because this is not really a broadcast media like ethernet, you need to provision a mesh of pvcs to create a virtual broadcast network.
The mapping can also be done dynamically, but the command " no fr inverse-arp" has disabled the dynamic mappings.
Maybe too much info for ccna though!

waru

that is definitely how it appears in the book!

So DLCI's do not need to be used on a point to point interface?

If you have 2 serial interfaces configured point to point would you then need to use DLCI's?

Cucumber

You still have to relate a DLCI to a point to point subinterface:

Router(config)#interface serial 0.15 point-to-point
Router(config-subif)#frame-relay interface-dlci 15