Transcript Chapter 6 – Connectivity Devices

Chapter 6 – Connectivity Devices
Types of Connectivity Devices
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Repeater
Hubs
Bridges
Switches
Routers
Gateways
Repeater
• Contains one input port and one output port
• Suited only to bus topology networks
• Allows you to extend the length of the bus
network
• Serve to amplify an analog or digital signal
• Work at the Physical Layer of OSI model
• In 10Base2 network, entire bus network cannot
exceed 1000 meters, so you can’t use more than 5
repeaters in sequence
Hub
• Contains multiple ports that connect to a group of
clients
• Can also use hub to connect servers, printers, as
well as other hubs
• Hub typically supports the star topology
• Hubs may be passive or intelligent
– Passive – does nothing but repeat signal
– Intelligent – Does internal processing such as permit
remote management and data filtering
Types of Hubs
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Stand alone hub
Stackable hubs
Modular hubs
Intelligent hubs
Stand Alone Hub
• Used to connect a small group of clients
together
• Not connected to other hubs in a tree or
daisy-chain fashion
• Usually contain 24 or less ports
• Should the hub fail, the entire network goes
down
Stackable Hubs
• Physically consist of multiple hubs sitting on top
of each other
• These are designed for the hubs to be linked
together
• Stackable hubs linked together logically represent
one large hub to the network
• Some us proprietary high-speed cabling to link the
hubs together
• For compatibility, it is best to use the same
manufacturer for all the stackable hubs in one unit
Modular Hubs
• More flexible by providing a number of interface
optins
• Similar to a PC
• Contains a system board and slots into which you
can insert different adapters which can connect the
hub to other hubs, routers, or the backbone
• You can attach redundant components to modular
hubs
• Offer the highest reliability of any of the hubs
Intelligent Hubs
• Can process data, monitor traffic, provide
troubleshooting information
• Information generated by hub can be stored
in a database
• This data can be used to determine problem
nodes
• Can identify nodes that are generating
unnecessary traffic
Bridges
• Look like repeaters in that bridges have a single
input and a single output port
• Differ from repeaters in that they can interpret the
data
• Bridges work a the Data Link Layer (2)
• Bridges analyze incoming frames (from one
segment) and determine if they should be
transmitted out the other segment
• The destination MAC address is used to decide
whether to retransmit or to discard the packet
• Bridge uses a Forwarding Table – See Fig. 6-22
Bridges – Continued
• Using Figure 6-22, see how the bridge
operates when Client #1 sends info to Client
#3
• What happens when Client #1 sends info to
Client # 6?
Bridges- Continued
• A bridge does not know initially what stations are
associated with what ports. The Forwarding Table
must be built
• Once a bridge is installed, it polls the clients on
each of its ports to provide their MAC address
• Once the bridge receives this information, it is
recorded in its Forwarding Table
• The filtering of traffic enhances the network
performance because the nodes spend less time
listening to packets that are not destined for them
Switches
• These operate at the Data Link Layer (2)
• They can interpret MAC address information just
like routers
• They resemble bridges and may be considered as
multiport bridges
• Each port on the switch can act like a bridge
• If a single device is connected to a port on a
switch, then it effectively receives its own
dedicated channel without the possibility of a
collision
• The switch turns the shared channel into several
Switches – Continued
• Each dedicated channel represents a
collision domain
• Switches have historically been used to
replace hubs
• Advantages of switches
– Secure because they isolate one device’s traffic
from another device’s traffic
– Provide separate channel for each device
Switches – Continued
• Disadvantages of switches
– Buffers inside switches can be overwhelmed by
heavy traffic and data loss can occur. The
devices sending the info do not detect this
situation. Higher-level protocols such as TCP
will detect the loss of data
Two Methods of Switching
• Cut-Through Mode
• Store and Forward
Cut-Through Mode
• Switch reads the frame header and decides where
to forward the data before it receives the entire
packet
• In this mode the switch begins transmitting the
packet before it receives the Frame Check
Sequence at the end of the frame, so it can’t verify
frame integrity
• It can detect packet fragments or runts
• Main advantage is its speed
• If switch is flooded with traffic, however, this is
not an advantage – data must be stored
Store and Forward Mode
• The switch reads the entire data frame into
memory and checks it for accuracy before
transmitting the information
• These type switches do not propagate data errors
• These can transfer data between segments using
different transmission speeds
• Example – Network printer is attached to a 100
Mbps port while the workstations that are to use
the printer may be connected to the switch through
10Mbps ports
VLANs
• Switches allow you to create virtual local
area networks by logically grouping a
number of ports into a broadcast domain
• The ports grouped together do not have to
reside on the same switch
• See Figure 6-24 as a example of a VLAN
• To create the VLAN, you must configure
the ports correctly
Routers
• Multiport device that connects dissimilar LANs
that use different transmission speeds and a variety
of protocols
• Operate at the Network Layer (Layer 3)
• Slower than switches or bridges because routers
use information from Layer 3 such as protocols
and logical addresses
• Routers are protocol dependent
• Keep track of locations of nodes on the network
• Determine the best path between two nodes
• Protocol being used must be routable (TCP/IP)
Routers – Continued
• All routers can perform the following:
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Connect dissimilar networks
Interpret Layer 3 (Network) information
Determine the best path from A to B
Reroute traffic if a particular path is down
• Some additional tasks the router might be able to
perform
– Prevent broadcast transmissions
– Prevent certain type of traffic from getting to a network
• Router Manufacturers: Cisco, Nortel
• See operation of router, figure 6-26
Routing Protocols
• Routers use routing protocols to determine the
best path from node A to node B in a network.
• These protocols used to collect data about the
current network status . From this data the routers
build a Routing Table
• Four most common routing protocols:
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RIP
OSPF
EIGRP
BGP
Gateways
• Used to connect two completely different
networks
• Gateways operate at the Application Layer
(7) of the OSI model