IBM SC30-3681-08 manual LAN Emulation Reliability, LAN Emulation Redundancy

Overview of LAN Emulation

Note: Broadcast Manager and Source Route Management are unavailable and cannot be enabled if bus-modeis set to adapter.

LAN Emulation Reliability

A perceived lack of robustness has been one of the most widely proclaimed criticisms of LAN emulation. While the ATM Forum is addressing this issue with speci®cations for distributing the LE service, the router offers an answer in the interim. Figure 17 provides a framework for describing the MSS redundancy solution.

Each LES/BUS may be independently con®gured for redundancy (the default is no

Figure 17. LAN Emulation Redundancy

redundancy). If redundancy is enabled, the LES/BUS is con®gured to assume the role of a primary or a backup LES/BUS. Unless it has been con®gured as a redundant LES/BUS, the LES/BUS is primary. The primary LES/BUS is typically the only LES/BUS visible to the LE clients. It is responsible for setting up and maintaining a Redundancy VCC to the backup LES. The presence of this VCC indicates that the primary LES/BUS is operational. The backup LES will not accept Control Direct VCC calls while the Redundancy VCC is established. However, if the Redundancy VCC is not present, the backup LES/BUS services ELAN requests in the usual manner.

For the redundancy protocol to be effective, LE clients must detect the failure of the primary LES/BUS and connect to the backup. LE clients detect server failures by means of released VCCs. Connection to the backup LES/BUS is accomplished through the LECS.

Upon receiving an LE_CONFIGURE_REQUEST, the LECS assigns the LE client to the appropriate LES and ELAN. If this LES has no con®gured backup, then the LECS returns the ATM address of the LES. If the LES is con®gured with a backup LES, then the LECS returns either the primary or backup LES address.

The LECS returns the backup LES address if the backup LES exists on the same MSS Server as the LECS and is currently serving the ELAN, if the primary LES exists on the same MSS Server as the LECS and it is not currently serving the ELAN, or if neither LES exists on the same MSS Server as the LECS and the client was last assigned to the primary LES (within the past 5 minutes). Otherwise, it returns the primary LES address to the LE client.

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