Establishing Frame Relay Connections

© 2002, Cisco Systems, Inc. All rights reserved.
Establishing Frame Relay Connections
Module 8
Objectives
Upon completing this module, you will be
able to:
Use Cisco IOS commands to configure an operational serial Frame Relay connection and Frame Relay subinterfaces, given a functioning router
Use show commands to identify anomalies in an operational serial Frame Relay connection and Frame Relay subinterfaces, given a functioning router
Use debug commands to identify events and anomalies in an operational serial Frame Relay connection and Frame Relay subinterfaces, given a functioning router and an operational serial Frame Relay connection
© 2002, Cisco Systems, Inc. All rights reserved.
4
Frame Relay Overview
Objectives
Upon completing this lesson, you will be
able to:
Describe the features and operation of a Frame Relay network
Define important Frame Relay terms including local access rate, virtual circuit, PVC, SVC, DLCI, CIR, InARP, LMI, FECN, and BECN
Frame Relay Overview
Connections made by virtual circuits
Connection-oriented service
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.
Frame Relay Terminology
Frame Relay default: nonbroadcast, multiaccess (NBMA)
Selecting a Frame Relay Topology
Reachability Issues with Routing Updates
Problem:
Broadcast traffic must be replicated for
each active connection.
Split-horizon rule prevents routing updates received on
one interface from being forwarded out the same interface.
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.
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’s network layer address.
Frame Relay Signaling
Cisco supports three LMI standards:
Cisco
ANSI T1.617 Annex D
ITU-T Q.933 Annex A
Frame Relay Inverse ARP
and LMI Signaling
Stages of Inverse ARP
and LMI Operation
How Service Providers Map Frame Relay DLCIs: Service Provider View
How Service Providers Map Frame Relay DLCIs: Enterprise View
Service Provider
Frame Relay-to-ATM Interworking
FRF.8 Service Interworking
Summary
Frame Relay is an ITU-T and ANSI standard that defines the process for sending data over a public data network.
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.
A Frame Relay NBMA topology may cause routing update reachability issues, which are solved by using subinterfaces.
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.
LMI is a signaling standard between the router and the Frame Relay switch that is responsible for managing the connection and maintaining status between the devices.
Service providers map Frame Relay DLCIs so that DLCIs with local significance appear at each end of a Frame Relay connection.
FRF.5 provides network interworking functionality that allows Frame Relay end users to communicate over an intermediate ATM network that supports FRF.5. FRF.8 provides service interworking functionality that allows a Frame Relay end user to communicate with an ATM
end user.