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.Figure 8-14 shows examples of LES connections.Figure 8-14 LAN emulation server (LES) connections.LAN EmulationServer (LES)AIPControl Distribute VCC(Point to Multipoint)Control Direct VCC(Unidirectional)Designing ATM Internetworks 8-19 Role of LANEFinding the BUSAfter the LEC has successfully joined the LES, its first task is to find the ATM address of the BUSand join the broadcast group.The LEC creates an LE_ARP_REQUEST packet with the MACaddress 0xFFFFFFFF.This special LE_ARP packet is sent on the Control Direct VCC to the LES.The LES recognizes that the LEC is looking for the BUS, responds with the ATM address of theBUS, and forwards that response on the Control Distribute VCC.Joining the BUSWhen the LEC has the ATM address of the BUS, its next action is to create a signaling packet withthat address and signal a Multicast Send VCC.Upon receipt of the signaling request, the BUS addsthe LEC as a leaf on its point-to-multipoint Multicast Forward VCC.At this time, the LEC hasbecome a member of the ELAN.Figure 8-15 shows examples of BUS connections.Figure 8-15 BUS connections.Broadcast andUnknown ServerAIPBus Forward VCC(Point to Multipoint)Bus Send VCC(Unidirectional)Address ResolutionThe real value of LANE is the ATM forwarding path that it provides for unicast traffic betweenLECs.When a LEC has a data packet to send to an unknown destination, it issues anLE_ARP_REQUEST to the LES on the Control Direct VCC.The LES forwards the request on theControl Distribute VCC, so all LEC stations hear it.In parallel, the unicast data packets are sent tothe BUS, to be forwarded to all endpoints.This flooding is not the optimal path for unicast traffic,and this transmission path is rate-controlled to 10 packets per second (per the LANE standard).Unicast packets continue using the BUS until the LE_ARP_REQUEST has been resolved.If bridging or switching devices with LEC software participate in the ELAN, they translate andforward the ARP on their LAN interfaces.One of the LECs should issue an LE_ARP_RESPONSEand send it to the LES, which forwards it to the Control Distribute VCC so that all LECs can learnthe new MAC-to-ATM address binding.When the requesting LEC receives the LE_ARP_RESPONSE, it has the ATM address of the LECthat represents the MAC address being sought.The LEC should now signal the other LEC directlyand set up a Data Direct VCC that will be used for unicast data between the LECs.8-20 Cisco CCIE Fundamentals: Network Design LANE ImplementationWhile waiting for LE_ARP resolution, the LEC forwards unicasts to the BUS.With LE_ARPresolution, a new optimal path becomes available.If the LEC switches immediately to the newpath, it runs the risk of packets arriving out of order.To guard against this situation, the LANEstandard provides a flush packet.When the Data Direct VCC becomes available, the LEC generates a flush packet and sends it to theBUS.When the LEC receives its own flush packet on the Multicast Forward VCC, it knows that allpreviously sent unicasts must have already been forwarded.It is now safe to begin using the DataDirect VCC.Figure 8-16 shows an example of a fully connected ELAN.Figure 8-16 Fully connected ELAN.AIP SubinterfacesLES BUSClient Direct VCC(Bidirectional)LANE ImplementationAs Table 8-3 indicates, the LANE functionality (the LECS, LEC, LES, and BUS) can beimplemented in different Cisco devices.Table 8-3 Cisco LANE ImplementationAvailable LANECisco Product Components Required Software ReleaseFamily of Catalyst 5000 switches LECS, LES, BUS, LEC ATM Module Software Version 2.0 or laterFamily of Catalyst 3000 switches LECS, LES, BUS, LEC ATM Module Software Version 2.1 or laterFamily of Cisco 7000 routers LECS, LES, BUS, LEC Cisco IOS Software Release 11.0 or laterFamily of Cisco 7500 routers LECS, LES, BUS, LEC Cisco IOS Software Release 11.1 or laterFamily of Cisco 4500 and 4000 routers LECS, LES, BUS, LEC Cisco IOS Software Release 11.1 or laterThese functions will be defined on ATM physical interfaces and subinterfaces.A subinterface canbe defined as a logical interface and is a part of a physical interface such as an Optical Carrier 3(OC-3) fiber.ATM interfaces on the Cisco routers and the ATM module on the Catalyst 5000 switchcan be logically divided into up to 255 logical subinterfaces.On the Catalyst 3000 switch, althoughthe same Cisco IOS Software code is used, the subinterface concept does not apply.The LEC can beconfigured using the menu-driven interface.Designing ATM Internetworks 8-21 LANE ImplementationThis section examines the implementation of ATM LANE networks and covers the following topics:" LANE Design Considerations" LANE RedundancyLANE Design ConsiderationsThe following are some general LANE design considerations:" The AIP provides an interface to ATM switching fabrics for transmitting and receiving data atrates of up to 155 Mbps bidirectionally.The actual rate is determined by the Physical layerinterface module (PLIM)." One active LECS supports all ELANs." In each ELAN, there is one LES/BUS pair and some number of LECs." The LES and BUS functionality must be defined on the same subinterface and cannot beseparated." There can be only one active LES/BUS pair per subinterface." There can be only one LES/BUS pair per ELAN." The current LANE Phase 1 standard does not provide for any LES/BUS redundancy." The LECS and LES/BUS can be different routers, bridges, or workstations." VCCs can be either switched virtual circuits (SVCs) or permanent virtual circuits (PVCs),although PVC design configuration and complexity might make anything more than a very smallnetwork prohibitively unmanageable and complex." When defining VLANs with the Catalyst 5000 switch, each VLAN should be assigned to adifferent ELAN
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