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coaxial cable
" LAN switches with ATM interfaces
ATM and VLANs
The Catalyst 3900 ATM expansion module supports up to 63 VLANs (or ELANs). Each ELAN corresponds to
a TrCRF. Each association between the ATM expansion module and a TrCRF creates a virtual ATM port. A
virtual ATM port is the equivalent of an LAN Emulation Client (LEC).
Understanding LAN Emulation
LANs can use connectionless service. However, ATM is always a connection-oriented service. Devices first use a
signaling process to establish a path with an ATM destination. Devices can send cell-based traffic only after the
devices have identifiers pointing to the connection path.
LANE uses point-to-multipoint connections to service the connectionless broadcast service that is required by
LAN protocols.
Cisco s Token Ring implementation of LANE makes an ATM interface look like one or more Token Ring
interfaces. Setting up LECs allows the Catalyst 3900 or Catalyst 5000 Token Ring module to operate in an ATM
LAN environment containing Cisco 7000 or Cisco 4500 series routers with ATM Interface Processor (AIP)
connected to a LightStream 1010 ATM switch.
Figure 5-1 illustrates the physical layout of an ATM network that uses LANE.
ATM and Token Ring LANE 5-5
Figure 5-1 Physical View of LANE
Router
Catalyst switch LightStream
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Figure 5-2 illustrates the logical view of the LANE network.
Figure 5-2 Logical View of LANE
Emulated LAN
Catalyst switch
LANE is an ATM service defined by the ATM Forum specification LAN Emulation over ATM
(ATM_FORUM 94-0035). This service emulates the following LAN-specific characteristics:
" Connectionless services
" Multicast services
" LAN MAC driver services
LANE service provides connectivity between ATM-attached devices and LAN-attached devices. This includes
connectivity between ATM-attached stations and LAN-attached stations as well as connectivity between
LAN-attached stations across an ATM network.
Because LANE connectivity is defined at the MAC layer, upper protocol-layer functions of LAN applications can
continue unchanged when the devices join ELANs. This feature protects corporate investments in legacy LAN
applications.
An ATM network can support multiple independent ELANs. Membership of an end system in any of the ELANs
is independent of the physical location of the end system. The end systems can move easily from one ELAN to
another, regardless of whether or not the hardware is moved.
Components of LANE
A Catalyst 3900 or Catalyst 5000 ATM module can participate in up to 63 of these ELANs.
LANE is defined on a client-server LAN model, as follows:
" LEC
An LEC emulates a LAN interface to higher layer protocols and applications. It forwards data to other LANE
components and performs LANE address resolution functions.
Each LEC is a member of only one ELAN. However, a router or a Catalyst ATM module can include LECs for
multiple ELANs: one LEC for each ELAN of which it is a member.
If a router has clients for multiple ELANs, the router can route traffic between the ELANs.
Note: If the Catalyst 3900 has multiple ATM modules and each has a client that is active for the same ELAN,
the Catalyst 3900 will not bridge between the ELANs on the different modules. The Catalyst 3900 acts as an
edge device on an ATM cloud (that is, there are no LANE services in the Catalyst 3900).
" LANE Server (LES)
The LANE server for an ELAN is the control center. It provides joining, address resolution, and address
registration services to the LANE clients in that ELAN. Clients can register destination unicast and multicast
MAC addresses with the LANE server. The LANE server also handles LANE ARP (LE_ARP) requests and
responses.
The current configuration is one LES per ELAN.
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" LANE Broadcast and Unknown Server (BUS)
The LANE BUS sequences and distributes multicast and broadcast packets and handles unicast flooding.
One combined LES and BUS is required per ELAN.
" LANE Configuration Server (LECS)
The LECS contains the database that determines which ELAN a device belongs to (each configuration server
can have a different named database). Each LEC contacts the LECS once, when it joins an ELAN, to determine
which ELAN it should join. The LECS returns the ATM address of the LES for that ELAN.
One LECS is required per ATM LANE switch cloud.
The LECS database can have the following four types of entries:
ELAN name, ATM address of LANE server pairs
LANE client MAC address, ELAN name pairs
LANE client ATM template, ELAN name pairs
Default ELAN name
Note: ELAN names must be unique on an interface. If two interfaces participate in LANE, the second interface
may be in a different switch cloud.
" Simple Server Redundancy Protocol (SSRP)
The LANE simple server redundancy feature creates fault tolerance using standard LANE protocols and
mechanisms. If a failure occurs on the LANE configuration server or on the LES/BUS, the ELAN can continue
to operate using the services of a backup LANE server.
The Catalyst 3900 ATM module currently supports only the LEC function. A Catalyst 5000 or a Cisco 7000,
Cisco 7200, Cisco 7500, RSP 7000, Cisco 4500, or Cisco 4700 with an AIP can supply all LANE functions.
LANE Operation and Communication
Communication among LANE components is typically handled by several types of VCCs. Some VCCs are
unidirectional; others are bidirectional. Some are point-to-point and others are point-to-multipoint. Figure 5-3
illustrates the various types of VCCs.
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Figure 5-3 LANE VCC Types
12 11
LE server LECS BUS
7 9
8
10
11
7
9
1 2 3
3 5 4
4
1
5 2
Client A Client B
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1 7 Control direct 4 9 Multicast send
2 8 Control distribute 5 10 Multicast forward
3 11 Configure direct (client) 6 6 Data direct
11 12 Configure direct (server)
The following section describes the processes involved with a client requesting to join an ELAN.
Join Process
The following process (illustrated in Figure 5-3) normally occurs after an LEC has been enabled on the ATM
module:
Step 1. The client requests to join an ELAN. The client sets up a connection to the LECS to find the ATM
address of the LANE server for its ELAN. See the bidirectional, point-to-point link (link 1 7 in
Figure 5-3).
An LEC finds the LECS using the following methods in the listed order:
" Locally configured ATM address
" Interim Local Management Interface (ILMI)
" Fixed address defined by the ATM Forum
Step 2. The LECS identifies the LES. Using the same VCC, the LECS returns the ATM address and the name of
the LES for the client s ELAN.
Step 3. The client tears down the configure direct VCC.
Step 4. The client contacts the server for its LAN. The client sets up a connection to the LES for its ELAN
(bidirectional, point-to-point control direct VCC [link 1 7 in Figure 5-3]) to exchange control traffic.
Once a control direct VCC is established between an LEC and LES, it remains up.
Step 5. The LES verifies that the client is allowed to join the ELAN. The server for the ELAN sets up a
connection to the LECS to verify that the client is allowed to join the ELAN (bidirectional,
point-to-point server configure VCC [link 11 12 in Figure 5-3]).
The server s configuration request contains the client s MAC address, its ATM address, and the name
of the ELAN. The LECS checks its database to determine whether the client can join that LAN; then it
uses the same VCC to inform the server whether or not the client is allowed to join.
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Step 6. The LES allows or disallows the client to join the ELAN. If allowed, the LES adds the LEC to the
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