A little more info regarding frame relay circuits:
Frame Relay is a NBMA (Non-broadcast Multi Access) network, meaning that it does not allow broadcast traffic between devices. This will cause a problem if you use distance-vector routing protocols such as RIP, because the split-horizon loop avoidance mechanism will prevent updates from going back out the interface on which they came. In a hub-and-spoke configuration, the spoke offices will not get updates about each other.
To avoid the split-horizon issues created in this instance, one could disable split-horizon and rely on the other loop-avoidance mechanisms (not recommended) or use subinterfaces.
Subinterfaces are logical interfaces attached to a single physical interface. The router sees and treats them as separate interfaces, however.
Multipoint subinterfaces do not solve the split-horizon issues and are essentially useless in Fream Relay circuits. They simply add multipoint interfaces to a logical interface, recreating all the same issues as a physical subinterface. Meh...
Point-to-point subinterfaces allow a single, physical interface to hold multiple ports. They are created using a "dot" - instead of Serial 0/0 we now have Serial 0/0.10. Each subinterface can connect a PVC of its own, and the router treats each like a different port.
hi greg, i am newly studying frame relay and actually i am confused when to use the physical interface, multipoint interface, or p2p interface. can you explain the advantage and disadvantage for each interface?
ReplyDelete