SNI configurations

This section describes some basic SNI configurations and their attributes.

Single gateway configuration: This configuration consists of one gateway VTAM® and one gateway NCP. This configuration is the easiest to configure and define, and cross-network session control is centralized. However, failure of the gateway NCP disrupts all cross-network sessions. This type of gateway can be used to connect up to 255 networks, with the gateway NCP residing in multiple nonnative networks.
Single gateway VTAM with multiple gateway NCPs: In this configuration, two or more NCPs act as the gateway NCPs. This configuration has the advantages of the single gateway configuration, but the failure of one gateway NCP does not disrupt all cross-network sessions.
Serial configuration: In this configuration, one gateway VTAM resides in a transport network and controls two or more gateway NCPs that connect to the nonnative networks. This configuration is best if the networks on either side of the transport network do not exchange much information.
Back-to-back configuration: This configuration consists of two gateway VTAMs and two gateway NCPs that connect through a null network. This configuration provides the most network isolation and security, but it requires more network definition. It also means that address and name translation must be performed twice, and the cross-network session path is longer. The SSCP-SSCP session between HOST2 and HOST3 in Figure 1 is an example of a back-to-back configuration.