The All-New Switch Book: The Complete Guide to LAN Switching Technology, Second Edition

3.2. Bridging Between Local and Wide Area Networks

In section 3.1, we considered the local interconnection of LANs using dissimilar technologies. In this section, we look at interconnecting remote LANs through an intervening Wide Area Network (WAN). While admittedly not a trivial task, bridging between LAN and WAN technologies is in many ways easier than bridging between dissimilar LANs. The problems and issues have more to do with the impact on application performance and vendor interoperability than with any particular implementation difficulty. In addition, WAN links are commonly used to interconnect bridges solely to other bridges; we generally do not need to consider direct end station attachments to a WAN link.

3.2.1. Applications of Remote Bridges

Up to now, all of the LANs in our catenets were assumed to be in the same place geographically; the bridged LAN environment spanned a building or a small campus. However, it is also possible to use transparent bridges to interconnect LANs in geographically separate locations, using intermediate WAN communications links between bridges, as depicted in Figure 3-14.^[]

^[] Remote interconnection can often be accomplished using either Data Link layer bridges or Network layer routers. The discussion in this chapter on the differences between LAN and WAN technology, and the decisions related to technology selection, are applicable both to the use of bridges or routers. The question of bridging versus routing is discussed in Chapter 4 ...