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A-6
B
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RIDGING AND
OUTING
Network Topology
If your network topology is star shaped, a
combination of ISDN and bridging is usually the
most efficient and successful option. Routing is a
better solution if your network topology is a complex
mix of both leased line and ISDN circuits, running at
64 Kbps to 2 Mbps.
Broadcast Storms
Bridges are programmed to automatically forward
data packets 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 stand-by, 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 dedicated links go in or out of
service. These changes in network topology are
handled by routing protocols. However, when using
the ISDN the source network can dial direct to the
destination network, and establish a point-to-point
bridged or routed connection. Generally, when
using this type of ISDN dial-up link, routing does not
provide much extra benefit.
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