Transcript Powerpoint - Chapter 3

Chapter Overview
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Bridging
Switching
Routing
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What Is a Bridge?
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A data-link layer device that connects
networks and filters packets
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Propagates only packets destined for the other
side of the bridge
Can reduce network traffic and collisions
Can lessen delays
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Connecting LANs with a Bridge
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Bridges and Collisions
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A collision domain is a network (or part of a network) that
is constructed so that a collision occurs when two
computers transmit packets at precisely the same time.
Adding a hub to a local area network (LAN) increases its
size but maintains a single collision domain because hubs
relay signals immediately at the physical layer, without
filtering them.
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Hubs do not relay packets immediately; they wait until the entire
packet is received.
Because the bridge delays propagation, computers on
opposite sides of the bridge transmitting at the same time
do not cause a collision.
Adding a bridge to a LAN splits it into two collision
domains, resulting in fewer collisions and increased
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efficiency.
Broadcasts
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Bridges and Broadcasts
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Bridges propagate all broadcast packets
without filtering them.
The network segments on either side of a
bridge are in the same broadcast domain.
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Transparent Bridging
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Transparent bridging is a method for
automatically compiling a bridge’s address
tables.
Bridges maintain an address table for each
network segment.
Bridges read the source and destination
addresses of packets and compare them to
the tables to determine whether to propagate
them.
When a bridge lacks the information needed
to filter a packet, it propagates the packet by
default.
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Bridge Types
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Local bridge. Connects network segments of
the same type and at the same location
Translation bridge. Connects network
segments at the same location that use
different media or different protocols
Remote bridge. Connects network segments
at remote locations, using a wide area
network (WAN) link
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Translation Bridge
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Switch Characteristics
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Data-link layer device
Replaces bridges and sometimes routers
Similar in appearance to a hub
Forwards incoming traffic out to the
destination port only
Converts a shared network medium to a
dedicated one
Offers advantages such as reduced network
congestion and the use of full network
bandwidth
Can operate in full-duplex mode
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Switching
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Replacing Routers with Switches
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Virtual LANs
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A virtual LAN (VLAN) is a subnet that exists
inside a switch.
Broadcasts sent by a computer go only to the
other computers in the VLAN.
Communications within a VLAN are switched.
Communications between VLANs can be
routed or switched.
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Layer 3 Switching
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Layer 3 switching minimizes the amount of
routing between VLANs because routing
occurs only when absolutely necessary.
A router establishes a connection between
systems and then switches take over.
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Switch Types
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A cut-through switch begins to forward
packets immediately.
A store-and-forward switch waits until the
entire packet arrives before forwarding it.
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Router Characteristics
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Connect networks together to form an
internetwork
Are network layer devices
Can connect LANs running different data-link
layer protocols
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Router Functions
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Forward packets to the destination network
Strip the data-link layer frames from incoming
packets and repackage the data into new
frames
Fragment packets when necessary
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Routing Process Example
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Hops
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Routing Tables
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Routing tables are essential to the router
operation and functions.
There are two methods of creating routing
tables:
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Static routing. Manual creation of routing table
entries by an administrator
Dynamic routing. Automatic creation of routing
table entries by using a specialized routing
protocol
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Router Types
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Routers can be stand-alone hardware devices
or software running on a computer.
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Hardware routers. Range from expensive
rackmounted devices to small stand-alone units
Software routers. Include Microsoft Windows 2000
Internet Connection Sharing (ICS), and Routing
and Remote Access
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Chapter Summary
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Bridging
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Switching
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Bridges selectively relay packets between network segments, depending on
their data-link layer destination addresses.
Bridges maintain a single broadcast domain and create separate collision
domains.
Switches improve on the function of bridges by forwarding packets only to
their destination systems.
Switches reduce the collisions on a network and increase the bandwidth
available to each computer.
Routing
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Routers are used to connect networks together at the network layer of the
OSI reference model.
Routers strip away the data-link layer frame of incoming packets and build a
new frame using the data-link layer protocol of the outgoing network.
Routing tables can be created manually by a network administrator or
automatically by a routing protocol.
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