Wide-Area Networking Configuration Guide: Frame Relay, Cisco IOS Release 12.2SX
Wide-Area Networking Overview
Wide-Area Networking Overview
Last Updated: October 7, 2011
Cisco IOS software provides a range of wide-area networking capabilities to fit almost every network environment need. Cisco offers cell relay via the Switched Multimegabit Data Service (SMDS), circuit switching via ISDN, packet switching via Frame Relay, and the benefits of both circuit and packet switching via Asynchronous Transfer Mode (ATM). LAN emulation (LANE) provides connectivity between ATM and other LAN types. The Cisco IOS Wide-Area Networking Configuration Guide presents a set of general guidelines for configuring the following software components:
This module gives a high-level description of each technology. For specific configuration information, see the appropriate module.
Finding Feature Information
Your software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the Feature Information Table at the end of this document.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
The Cisco Frame Relay implementation currently supports routing on IP, DECnet, AppleTalk, XNS, Novell IPX, CLNS, Banyan VINES, and transparent bridging.
Although Frame Relay access was originally restricted to leased lines, dialup access is now supported. For more information about dialer profiles or legacy dial-on-demand routing (DDR), see the module Dial-on-Demand Routing Configuration.
To install software on a new router or access server by downloading software from a central server over an interface that supports Frame Relay, see the module Loading and Maintaining System Images.
To configure access between Systems Network Architecture (SNA) devices over a Frame Relay network, see the module Configuring SNA Frame Relay Access Support.
The Frame Relay software provides the following capabilities:
Frame Relay-ATM Internetworking
Cisco IOS software supports the Frame Relay Forum implementation agreements for Frame Relay-ATM Interworking. Frame Relay-ATM Interworking enables Frame Relay and ATM networks to exchange data, despite differing network protocols. There are two types of Frame Relay-ATM Interworking:
FRF.5 Frame Relay-ATM Network Interworking
FRF.5 provides network interworking functionality that allows Frame Relay end users to communicate over an intermediate ATM network that supports FRF.5. Multiprotocol encapsulation and other higher-layer procedures are transported transparently, just as they would be over leased lines.
FRF.5 describes network interworking requirements between Frame Relay Bearer Services and Broadband ISDN (BISDN) permanent virtual circuit (PVC) services.
The FRF.5 standard is defined by the Frame Relay Forum Document Number FRF.5: Frame Relay/ATM PVC Network Interworking Implementation Agreement. For information about which sections of this implementation agreement are supported by Cisco IOS software, see Frame Relay-ATM Interworking Supported Standards.
FRF.8 Frame Relay-ATM Service Interworking
FRF.8 provides service interworking functionality that allows a Frame Relay end user to communicate with an ATM end user. Traffic is translated by a protocol converter that provides communication among dissimilar Frame Relay and ATM equipment.
FRF.8 describes a one-to-one mapping between a Frame Relay PVC and an ATM PVC.
The FRF.8 standard is defined by the Frame Relay Forum Document Number FRF.8: Frame Relay/ATM PVC Network Service Interworking Implementation Agreement. For information about which sections of this implementation agreement are supported by Cisco IOS software, see Frame Relay-ATM Interworking Supported Standards.
Switched Multimegabit Data Service
The Cisco implementation of the SMDS protocol is based on cell relay technology as defined in the Bellcore Technical advisories, which are based on the IEEE 802.6 standard. We provide an interface to an SMDS network using DS1 or DS3 high-speed transmission facilities. Connection to the network is made through a device called an SDSU--an SMDS digital service unit (DSU). The SDSU attaches to a router or access server through a serial port. On the other side, the SDSU terminates the line.
The implementation of SMDS supports the IP, DECnet, AppleTalk, XNS, Novell IPX, Banyan VINES, and OSI internetworking protocols, and transparent bridging.
The implementation of SMDS also supports SMDS encapsulation over an ATM interface. For more information and for configuration tasks, see Configuring ATM.
Routing of AppleTalk, DECnet, IP, IPX, and ISO CLNS is fully dynamic; that is, the routing tables are determined and updated dynamically. Routing of the other supported protocols requires that you establish a static routing table of SMDS neighbors in a user group. Once this table is set up, all interconnected routers and access servers provide dynamic routing.
The SMDS implementation includes multiple logical IP subnetworks support as defined by RFC 1209. This RFC describes routing IP over an SMDS cloud in which each connection is considered a host on one specific private network, and points to cases where traffic must transit from network to network.
The implementation of SMDS also provides the Data Exchange Interface (DXI) Version 3.2 with heartbeat . The heartbeat mechanism periodically generates a heartbeat poll frame.
When a multicast address is not available to a destination, pseudobroadcasting can be enabled to broadcast packets to those destinations using a unicast address.
Link Access Procedure - Balanced and X.25
X.25 is one of a group of specifications published by the ITU-T. These specifications are international standards that are formally called Recommendations . The ITU-T Recommendation X.25 defines how connections between DTE and DCE are maintained for remote terminal access and computer communications. The X.25 specification defines protocols for two layers of the Open Systems Interconnection (OSI) reference model. The data link layer protocol defined is LAPB. The network layer is sometimes called the packet level protocol (PLP), but is commonly (although less correctly) referred to as the X.25 protocol.
The ITU-T updates its Recommendations periodically. The specifications dated 1980 and 1984 are the most common versions currently in use. Additionally, the International Standards Organization (ISO) has published ISO 7776:1986 as an equivalent to the LAPB standard, and ISO 8208:1989 as an equivalent to the ITU-T 1984 Recommendation X.25 packet layer. The Cisco X.25 software follows the ITU-T 1984 Recommendation X.25 , except for its Defense Data Network (DDN) and Blacker Front End (BFE) operation, which follow the ITU-T 1980 Recommendation X.25 .
In addition to providing remote terminal access, The Cisco X.25 software provides transport for LAN protocols--IP, DECnet, XNS, ISO CLNS, AppleTalk, Novell IPX, Banyan VINES, and Apollo Domain--and bridging.
Cisco IOS X.25 software provides the following capabilities:
The Cisco X.25 implementation does not support fast switching.
Layer 2 Virtual Private Network
L2VPN services are point-to-point. They provide Layer 2 point-to-point connectivity over either an MPLS or a pure IP (L2TPv3) core.
Layer 2 Tunneling Protocol Version 3
Layer 2 Tunneling Protocol Version 3 (L2TPv3) expands Cisco support of Layer 2 Virtual Private Networks (VPNs). L2TPv3 is an Internet Engineering Task Force (IETF) l2tpext working group draft that provides several enhancements to L2TP for the capability to tunnel any Layer 2 payload over L2TP. Specifically, L2TPv3 defines the L2TP protocol for tunneling Layer 2 payloads over an IP core network using Layer 2 virtual private networks (VPNs).
L2VPN Pseudowire Redundancy
L2VPNs can provide pseudowire resiliency through their routing protocols. When connectivity between end-to-end PE routers fails, an alternative path to the directed LDP session and the user data can take over. However, there are some parts of the network where this rerouting mechanism does not protect against interruptions in service. The L2VPN Pseudowire Redundancy feature provides the ability to ensure that the CE2 router in can always maintain network connectivity, even if one or all the failures in the figure occur. The L2VPN Pseudowire Redundancy feature enables you to set up backup pseudowires. You can configure the network with redundant pseudowires (PWs) and redundant network elements.
Layer 2 Virtual Private Network Interworking
Layer 2 transport over MPLS and IP already exists for like-to-like attachment circuits, such as Ethernet-to-Ethernet or PPP-to-PPP. L2VPN Interworking builds on this functionality by allowing disparate attachment circuits to be connected. An interworking function facilitates the translation between the different Layer 2 encapsulations. The L2VPN Interworking feature supports Ethernet, 802.1Q (VLAN), Frame Relay, ATM AAL5, and PPP attachment circuits over MPLS and L2TPv3.
Layer 2 Local Switching
Local switching allows you to switch Layer 2 data between two interfaces of the same type (for example, ATM to ATM, or Frame Relay to Frame Relay) or between interfaces of different types (for example, Frame Relay to ATM) on the same router. The interfaces can be on the same line card or on two different cards. During these kinds of switching, the Layer 2 address is used, not any Layer 3 address. Same-port local switching allows you to switch Layer 2 data between two circuits on the same interface.
Wide Area Application Services
Cisco's WAAS Express software interoperates with WAN optimization headend applications from Cisco and improves WAN access and use by optimizing applications that require high bandwidth or are bound to a LAN, such as backup.
WAAS Express helps enterprises meet the following objectives:
The Network Analysis Module (NAM) Performance Agent (PA) for WAAS Express analyzes and measures network traffic. The PA enables baselining, monitoring, and troubleshooting of application performance. The analysis and measurement of network traffic is done by the Measurement, Aggregation, and Correlation Engine (MACE). MACE performs the required measurements on a subset of traffic and exports the necessary metrics to a target.
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