Hi NetPros, I'm trying to understand frame-relay and the way it works a little bit more in depth. I'm kind of confused with the Layer2-to-Layer3 mapping.
With point-to-point subinterfaces is the DLCI used to send frames implied because the receiving router will see the DLCI and realize it can only come from one possible host?
When 2 or more PVCs terminate on a router is it necessary to have this mapping in order to avoid DLCI confusion?
If so, what examples would you prefer frame-relay map configuration opposed to inverse ARP and vice versa!
For a hub-and-spoke system, you can have a multipont (or physical) interface at the hub, and p2p subinterfaces at the spokes. At the hub, configure a frame map for each spoke, or allow it to learn the address of each spoke by inverse-arp.
From the p.o.v. of spoke-to-spoke communication, there shoud be no problem. Each spoke will forward all traffic for the subnet up to the hub, because the P2P inteface will have a mask that covers all the spokes as well as the hub.
As far as the routing protocols are concerned, you would need to switch off split-horizon for RIP or EIGRP. If you don't do that, the spokes will still be able to get to each other on the FR subnet, but the hub would not pass any branch-office LAN prefixes from spoke to spoke.
OSPF is a little more complicated. You should make sure that the hub is the DR, and in that way it will reflect any prefix advertised by a spoke to each other spoke. The best way to do that is to configure ip ospf priority 0 on the spokes.
Alternatively, define the OSPF network type as point-to-multipoint. That way there would no longer be any DR, but the hub would treat each link like a seperate P2P network as far as LSAs are concerned.
Does that make sense?