© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—6-1 Establishing Serial Point-To-Point Connections Introducing Frame Relay

© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—6-2 Outline Overview Frame Relay Overview Frame Relay Stack Layered Support Frame Relay Terminology Frame Relay Topologies Reachability Issues in Frame Relay Reachability Issue Resolution Frame Relay Address Mapping Frame Relay Signaling How Service Providers Map Frame Relay DLCIs Service Provider Frame Relay-to-ATM Interworking Summary

© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—6-3 Frame Relay Overview Connections made by virtual circuits Connection-oriented service

© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—6-4 Frame Relay Stack OSI Reference Model Frame Relay Physical Presentation Session Transport Network Data Link Application EIA/TIA-232, EIA/TIA-449, V.35, X.21, EIA/TIA-530 Frame Relay IP/IPX/AppleTalk, etc.

© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—6-5 Frame Relay Terminology

© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—6-6 Frame Relay default: NBMA Selecting a Frame Relay Topology

© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—6-7 Problem: Broadcast traffic must be replicated for each active connection. Split horizon rule prevents routing updates received on an interface from being forwarded out the same interface. Reachability Issues with Routing Updates

© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—6-8 Resolving Reachability Issues Split horizon can cause problems in NBMA environments. Subinterfaces can resolve split-horizon issues. Solution: A single physical interface simulates multiple logical interfaces.

© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—6-9 Frame Relay Address Mapping Use LMI to get locally significant DLCI from the Frame Relay switch. Use Inverse ARP to map the local DLCI to the remote router network layer address.

© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—6-10 Frame Relay Signaling Cisco supports three LMI standards: –Cisco –ANSI T1.617 Annex D –ITU-T Q.933 Annex A

© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—6-11 Frame Relay Inverse ARP and LMI Signaling

© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—6-12 Stages of Inverse ARP and LMI Operation

© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—6-13 How Service Providers Map Frame Relay DLCIs: Service Provider View

© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—6-14 How Service Providers Map Frame Relay DLCIs: Enterprise View

© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—6-15 Service Provider Frame Relay-to-ATM Internetworking

© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—6-16 FRF.8 Service Internetworking

© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—6-17 Summary Frame Relay is a connection-oriented data-link technology that is streamlined to provide high performance and efficiency. The core aspects of Frame Relay function at the lower two layers of the OSI reference model. Knowing the terms that are used frequently when discussing Frame Relay is important to understanding the operation and configuration of Frame Relay services. Frame Relay allows you to interconnect your remote sites in a variety of topologies including star, full mesh, and partial mesh. Two problems that Frame Relay NBMA topology may cause include reachability issues regarding routing updates and the need to replicate broadcasts onto each PVC when a physical interface contains more than one PVC. Two methods to resolve the reachability issue brought on by split horizon are turning off split horizon and using a fully meshed topology.

© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—6-18 Summary (Cont.) A Frame Relay connection requires that on a VC, the local DLCI be mapped to a destination network layer address, such as an IP address. Cisco routers try to autosense which LMI type the Frame Relay switch is using by sending one or more full LMI status requests to the Frame Relay switch. The Frame Relay switch responds with one or more LMI types, and the router configures itself with the last LMI type received. Service providers map Frame Relay DLCIs so that DLCIs with local significance appear at each end of a Frame Relay connection. FRF.5 provides internetworking functionality that allows Frame Relay end users to communicate over an intermediate ATM network that supports FRF.5. FRF.8 provides service internetworking functionality that allows a Frame Relay end user to communicate with an ATM end user.

© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—6-19