Understanding the network.pdf - Back to Home

and so on) should be localized as groups on each side of the router or
bridge. This way, the available bandwidth is shared between localized
end-stations, and the bridge or router is only used for
segment/network data exchanges. Although this seems like a
relatively straightforward idea, it is the most common network design
mistake made. When expanding or changing the topology of the
network, it is vital that you identify how the end-stations on the
network interact with each other.
If you have 300 users sending print jobs over a router because all the
printers are on a separate network, or have six different workgroups
of users who, for the most part, exchange files among themselves on
their own local common Ethernet segment, the network is not
designed to meet the data flow of the users connected to it. A more
sensible approach is to have printers distributed across different
networks so the traffic is localized. Segmenting Ethernet users into
smaller localized collision domains will minimize bandwidth contention,
resulting in better available bandwidth utilization. This also is true for
Token Ring users, even though token-based technologies allocate
bandwidth more efficiently. The larger the node count on the ring, the
longer the distance between transmission times. The network's traffic
flow dictates how well the network will perform. If routers and bridges
are placed badly, the network performance can suffer substantially,
and might be even worse in some cases than before they were
installed.
In most LAN situations, bridging is a more efficient (from a
performance and cost perspective) means for addressing Layer 2
performance and expansion problems than introducing a new router.
This is particularly true when you are integrating media types of
similar or higher speeds. One popular and common example is the use
of translation (or encapsulation) bridges to connect Ethernet and
Token Ring network segments to FDDI backbones. This can provide
reliable redundant transport at 5 to 25 percent performance
improvements for Token Ring and 10 percent for Ethernet. Another
very common application of the translation bridge is the variation
known as the WAN or remote bridge. Remote bridges use dedicated
WAN point-to-point links to connect remote LAN segments together.
This approach is common on networks that use Layer 3 protocols that
do not support routing well, such as AppleTalk phase 1 or DEC's Local
Area Transport (LAT), which doesn't route at all.
It is appropriate to use routers to address Layer 3 networking issues.
Most often, these are issues like network security or access. Other
common Layer 3 issues include network application performance,