IBM SC30-3681-08 manual Overview of the Lecs Function

Overview of LAN Emulation

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 con®gured with the ATM address of the LES that serves its ELAN. The LECS reduces the network management burden by serving as a centralized repository for con®guration data, minimizing con®guration of the LE clients.

Note: At most, one LECS is con®gurable on each router.

Clients connect to the LECS using well-de®ned 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 con®gured LECS address information (con®guration of an LECS ATM address at LE clients is optional and isnot 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 ATM address as de®ned 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. Con®guring 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 ATM switch support all three methods: the pre-con®gured LECS address, ILMI connection, and the well-known LECS ATM address.

The LECS must provide initial con®guration data to LE clients. The most crucial piece of data is the ATM address 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 identi®es an LE client using information in the LE_CONFIGURATION_REQUEST frame sent by the LE client. The con®guration 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 con®guration request:

1.Primary ATM address of the LE client

This ®eld is required and uniquely identi®es the LE client.

2.LAN destination associated with the LE client

This ®eld can contain a MAC address or a route descriptor that uniquely identi®es the LE client or it can be unspeci®ed.

3.ELAN Name

This ®eld 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 unspeci®ed in the request.

4.ELAN Type

This ®eld can specify that the LE client belongs to an Ethernet or Token-Ring ELAN, or it can be unspeci®ed. If the LE client speci®es 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

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