C H A P T E R24
• Understand bridging in a mixed Ethernet and Token Ring environment.
• Describe the differences between source-route transparent and translational bridging.
• List some of the challenges of translational bridging.
Transparent bridges are found predominantly in Ethernet networks, and source-route bridges (SRBs) are
found almost exclusively in Token Ring networks. Both transparent bridges and SRBs are popular, so it
is reasonable to ask whether a method exists to directly bridge between them. Several solutions have
Translational bridging provides a relatively inexpensive solution to some of the many problems involved
with bridging between transparent bridging and SRB domains. Translational bridging first appeared in
the mid- to late-1980s but has not been championed by any standards organization. As a result, many
aspects of translational bridging are left to the implementor.
In 1990, IBM addressed some of the weaknesses of translational bridging by introducing source-route
transparent (SRT) bridging. SRT bridges can forward traffic from both transparent and source-route end
nodes and can form a common spanning tree with transparent bridges, thereby allowing end stations of
each type to communicate with end stations of the same type in a network of arbitrary topology. SRT is
specified in the IEEE 802.1d Appendix C.
Ultimately, the goal of connecting transparent bridging and SRB domains is to allow communication
between transparent bridges and SRB end stations. This chapter describes the technical problems that
must be addressed by algorithms attempting to do this and presents two possible solutions: translational
bridging and SRT bridging.
Many challenges are associated with allowing end stations from the Ethernet/transparent bridging
domain to communicate with end stations from the SRB/Token Ring domain:
rnetworking Technologies Handbook
Chapter 24 Mixed-Media Bridging