In the AS/400 environment, SNA Server uses a combination of LU names and LU aliases over one or more servers to achieve transparent multiple connections to an AS/400.
Figure 6.10 Fault tolerance for an AS/400.
A single SNA Server computer can use multiple connections to provide fault tolerance. To use this method, two or more APPC connections to the same AS/400 are configured as hot backups for one another. If one of the connections fails, the clients are reconnected to select a working configuration.
SNA Server can also use multiple SNA Server computers as backups to one another. If one of the servers fails, the clients are shifted from the failed server to a working server.
Using a combination of hot backup across connections and servers is recommended to maintain a high level of host availability in your enterprise.