White Paper Abstract:
The purpose of this document is to provide the different options available to customers who wish to implement Data-Link Switching Plus (DLSw+) Ethernet Redundancy. Because of the levels of redundancy built into customer environments (particularly in the campus networks) and the nature of switched Ethernet technology, this often creates an inherent problem when connecting SNA clients over DLSw+ with multiple paths to the host. SNA devices historically ran across Token Ring (via source-route bridging), and multiple paths were possible by means of the Routing Information Field (RIF). The RIF was basically a field in the Token Ring frame that plotted the "route" (bridge number, ring number) from a source to destination, providing a unique series of coordinates. Transparent bridging does not use a RIF, so it is impossible to tell whether a frame has already traversed a particular domain, creating an opportunity for loops.