Networkdevices by Jetarvind kumar madhukar

Network Devices
Repeaters, hubs, bridges,
switches, routers, NIC’s

Devices and the layers at
which they operate
Layer Name of Layer Device
3 Network Routers, layer 3
switches
2 Data Link Switches,
bridges, NIC’s
1 Physical Hubs

NIC’s
(Network Interface Cards)
 This NIC has interfaces for twisted pair,
thicknet, and thinnet connectors.

Repeaters
 Signal attenuation or signal loss – signal
degrades over distance
 Repeaters clean, amplify, and resend signals
that are weakened by long cable length.
 Built-in to hubs or switches

Hubs
 OSI layer 1 hardware
 Hubs regenerate and retime network signals
 Hubs propagate signals through the network
 They cannot filter network traffic
 They cannot determine best path
 They are used as network concentration points
 They are really multi-port repeaters
 Uplink port – crossover mode or straight through
mode

Bridges
 A layer 2 device designed to create two or
more LAN segments, each of which is a
separate collision domain.
 The purpose is to filter traffic on a LAN, to
keep local traffic local, yet allow connectivity
to other segments of the network.
 Filter traffic by looking at the MAC address
 Frame filtering

Bridges
 If the frame is addressed to a MAC address
on the local side of the bridge, it is not
forwarded to the other segment
 MAC addresses on the other segment are
forwarded
 Bridges maintain a MAC address table for
both segments they are connected to

Cycle of bridges
 Bridged network can span many segments
 Broadcasts are sent to all segments

Bridges
Distributed Spanning Tree
 If all bridges forward broadcasts, infinite
loops can occur
 Bridges perform DST on boot to determine
which bridges will not forward broadcasts

Switched networks
 Shared ethernet networks perform best when
kept to 30-40 percent full capacity
 This is a result of CSMA/CD
 A LAN switch is a high-speed multiport bridge
which segments each port into its own
collision domain and can access the full
bandwidth

Switches
 Each port is a simulated segment to itself

Store and Forward Switches
 Do error checking on each frame after the entire
frame has arrived into the switch
 If the error checking algorithm determines there is
no error, the switch looks in its MAC address table
for the port to which to forward the destination
device
 Highly reliable because doesn’t forward bad frames
 Slower than other types of switches because it holds
on to each frame until it is completely received to
check for errors before forwarding

Cut Through Switch
 Faster than store and forward because
doesn’t perform error checking on frames
 Reads address information for each frame as
the frames enter the switch
 After looking up the port of the destination
device, frame is forwarded
 Forwards bad frames
 Performance penalty because bad frames can’t
be used and replacement frames must be sent
which creates additional traffic

Fragment free cut through
switch
 Combines speed of cut through switch with
error checking functionality
 Forwards all frames initially, but determines
that if a particular port is receiving too many
bad frames, it reconfigures the port to store
and forward mode
 Preferred switching solution

Unmanaged/Intelligent
switches
 Unmanaged – provides LAN’s with all the
benefits of switching
 Fine in small networks
 Intelligent switches tracks and reports LAN
performance statistics
 Have a database ASIC (application specific
integrated circuit) on board to collect and
store data which you view through a software
interface

Layer 3 switch
 By definition a switch filters or forwards frames
based on MAC addresses. This makes a switch a
layer 2 device.
 Now we have layer 3 switches which have routing
capability. If a data frame can’t be switched it is
routed.
 Each port is a separate LAN port, but the forwarding
engine actually calculates and stores routes based
on IP addresses, not MAC addresses
 Usually support only IP or IP and IPX

VLAN Switches
 Virtual local area network
 Each port on a switch defines a collision domain
 The entire switch forms a single broadcast domain
 VLANs can define multiple broadcast domains
 Network traffic that is directed to all computers on
the network can be segmented to transmit only on a
specific VLAN.
 Improves bandwidth on a the VLAN’s because each
VLAN filters the network-to-network broadcast traffic
as well as the collision traffic from other VLAN’s

Physical Layer Broadcast
 Physical layer broadcasts – implemented by
non-switched Ethernet networks through
shared cabling and hubs
 Each bit that is transmitted is physically received
by every station
 Switches and VLAN’s don’t do physical layer
broadcasts

MAC-level broadcast
 MAC-level broadcast – deal with how to handle
MAC level broadcast frames; that is the data frames
that have a broadcast destination MAC address
 MAC-level broadcast frames are addressed to all
MAC addresses on a given network (not a network
segment, but an actual network as defined by its
network address)
 A regular switch forwards all broadcast frames out
all ports, but a VLAN switch forwards broadcast
frames only to ports that are part of the same VLAN
 Multiple switches can be part of the same VLAN

VLAN Switches
 None of the VLAN’s can communicate unless
each VLAN is connected to a router or layer 3
switch
 Each VLAN is separating collision traffic
associated with MAC Addresses (layer 2) and
each VLAN is separating the network-to-
network broadcast traffic. In other words each
VLAN is acting as a separate network so a
layer 3 device is necessary for them to
communicate

Networkdevices by Jetarvind kumar madhukar

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Networkdevices by Jetarvind kumar madhukar