Overview of the LECS Function
LE clients are not required to use the LECS, although it is recommended. If the
LECS is not used, each LE client must be configured with the ATMaddress of the
LES that serves its ELAN. The LECS reduces the network management burden by
serving as a centralized repository for configuration data, minimizing configuration of
the LE clients.
Note: At most, one LECS is configurable on each router.
Clients connect to the LECS using well-defined procedures. The following steps are
attempted by a client, in order, until a virtual channel connection (VCC) to the LECS
is established:
1. Connect to the LECS using any configured LECS address information
(configuration of an LECS ATMaddress at LE clients is optional and is
not
recommended).
2. Obtain a list of LECS addresses using ILMI and attempt to connect to each
LECS on the list, in order, until a VCC is established.
3. Establish a VCC to the well-known LECS ATMaddress as defined by the ATM
Forum.
As previously stated, ILMI is the preferred method for LE clients to locate the LECS.
The well-known LECS address is needed because some switches do not support
the ILMI method. Configuring the LECS address at the LE clients should be done
only
when the switch does not support the ILMI method and the LE service does
not support the well-known LECS address.
The router and the IBM ATMswitch support all three methods: the pre-configured
LECS address, ILMI connection, and the well-known LECS ATMaddress.
The LECS must provide initial configuration data to LE clients. The most crucial
piece of data is the ATMaddress of the LES. To provide this information to an LE
client, the LECS must be able to identify the LE client and to determine the correct
LES for that LE client. The LECS identifies an LE client using information in the
LE_CONFIGURATION_REQUESTframe sent by the LE client. The configuration
request can also contain information to identify the ELAN that the LE client is
seeking to join. The following information can be included in the configuration
request:
1. Primary ATMaddress of the LE client
This field is required and uniquely identifies the LE client.
2. LAN destination associated with the LE client
This field can contain a MAC address or a route descriptor that uniquely
identifies the LE client or it can be unspecified.
3. ELAN Name
This field can contain a name identifying the requested ELAN or the requesting
LE client. In the router implementation, ELAN names are standard ASCII strings.
The ELAN name can be unspecified in the request.
4. ELAN Type
This field can specify that the LE client belongs to an Ethernet or Token-Ring
ELAN, or it can be unspecified. If the LE client specifies the type of ELAN, the
LECS cannot assign the client to an ELAN of a different type.
5. Maximum frame size supported by the LE client
Overview of LAN Emulation
260 MRS V3.2 Software User’s Guide