This chapter describes Proteon's Adaptive Source Route Transparent (ASRT) bridge. It includes the following sections:
About ASRT
Transparent-Source Routing Compatibility - Issues and Solutions
About ASRT
The ASRT bridge is a software collection of several bridging options. ASRT combines transparent bridging and source route bridging so that they can either function separately or be combined as a single ASRT bridge. This extended functionality allows communication between a strict source-routing end station and a transparent end station. Depending on the configuration commands used, the ASRT bridge provides the following bridging options:
The difference in the bit transmission standard means that a bridge from LSB to MSB LANs has to reverse the bit order of the destination and source MAC addresses at the start of the MAC frame. This is because the different LAN types use the same bit order for the MAC address (i.e., group bit first) and yet use a different bit order for the user data: either LSB or MSB first. The misinterpretation of addresses due to reversed bit ordering is compounded by the fact that some of the high-level communications protocols misinterpret MAC addresses altogether. Protocols like IP, IPX, and VINES misinterpret bridging addresses because at the time of their initial development, there was no standard representation of MAC addresses. The bit order differential is best resolved by combining bridging technology (data link layer technology) with routing technology (network layer technology). Rather than asking the user to reverse engineer today's communications protocols and configure each bridge to flip or reverse addresses on a case-by-case basis, the problem is more easily solved by routing these protocols. Routing eliminates the bit-order and protocol-addressing problems by accessing the detailed packet addresses running at the higher layer. Routing alone is not a complete solution, since other protocols such as IBM Frames and NetBIOS cannot be routed, and SNA routing is limited. Therefore, it is important to implement SRT in a device where bridging and routing work hand-in-hand. ASRT, the Proteon implementation of SRT, resides in all of its routers.