3Com 3C840 - Manual (Page 168)

A-6 A PPENDIX A: B RIDGING AND R OUTING
other bridges detect this and reconfigure their ports so that there is once
again an active data path through the network.
Network Topology If your network topology is star shaped, a combination of analog
modems and bridging is usually the most efficient and successful option.
Routing is a better solution if your network is a complex mix of WAN
interconnects and/or multiple protocols.
Broadcast Storms Bridges are programmed to forward data packets automatically by
default while routers filter data packets by default. These attributes have
an impact on the overall flow of data across the network. Much has been
made of broadcast storms in connection with bridged networks, where
the broadcast signals from bridges propagate to fill all of the wide area
bandwidth, and bring the network down. Broadcast storms cannot be
attributed to installation of bridges or routers, but by poor protocol
implementation and network design. However the deployment of routers
can effectively firewall one logical network from another.
Optimum Use of
Resource
Bridged networks use Spanning Tree Protocol (STP) to provide network
resilience, by retaining redundant links on standby, in case the primary
link fails. This means that you are not making maximum use of available
resources.
Routing protocols make each node aware of the primary and alternate
routes available, ensuring that resources (particularly WAN links) are not
wasted.
Routers have been designed to provide the optimum route through the
network from the workstation through to the destination resource with
which the user wishes to communicate. In a very large network there
could be multiple paths available, and these could change as links go in
or out of service. These changes in network topology are handled by
routing protocols.
Network
Organization,
Structure, and
Physical Layout Some organizations are structured into departments determined by the
physical layout of their work environment, so it is natural to divide the
corporate network into separate logical networks. Routing becomes the
obvious candidate for handling these individual LANs.
840ug.book Page 6 Friday, July 7, 2000 2:23 PM