treatment of broadcasts and multicasts. Remembering the concepts of collision domains,
broadcast domains, and how each device separates LANs into different domains is one key to
understanding campus LAN design and troubleshooting.
switched networks. A thorough understanding of Spanning Tree also is important for CCNP and
CCIE certification; the basics are required for CCNA certification.
Protocol. One is a book by Radia Perlman called Interconnections: Bridges, Switches, and
Routers. The other is the Cisco Press book Cisco LAN Switching, by Kennedy Clark and Kevin
Hamilton. Both books cover Spanning Tree in a clear and detailed manner; the Cisco Press book
also covers implementation details on Cisco's LAN switching products. Perlman's book has
been a long-time favorite of mine, but the Clark and Hamilton book has recently been added to
my list of top five favorite (computer) books.
network in which only one active path exists between any pair of LAN segments (collision
domains). To accomplish this task, all bridging devices, including switches, use a dynamic
protocol. The result of the protocol is that each interface on a bridging device will settle into a
blocking state or a forwarding state. Blocking means that the interface cannot forward or
receive data frames, but it can send and receive Configuration Bridge Protocol Data Units
(CBPDUs); forwarding means the interface can both send and receive data frames. By having
a correct subset of the interface's block, a single currently active logical path will exist between
each pair of LANs.
transparent bridge or a LAN switch. If a distinction between the two needs to be made, the terms
transparent bridge or switch will be used.
destined for unknown MAC addresses, or broadcasts, will be forwarded infinitely by the
bridges.