DEPARTMENT OF INFORMATION TECHNOLOGY

PRACTICAL NO. 3
OBJECTIVE: Study and familiarization with various network devices.

THEORY:

Network Devices: Network devices, or networking hardware, are physical devices that are required for
communication and interaction between hardware on a computer network.

Types Of Network Devices:

HUB:
Hubs connect multiple computer networking devices together. A hub also acts as a repeater in that it
amplifies signals that deteriorate after traveling long distances over connecting cables. A hub is the
simplest in the family of network connecting devices because it connects LAN components with identical
protocols.

A hub can be used with both digital and analog data, provided its settings have been configured to prepare
for the formatting of the incoming data. For example, if the incoming data is in digital format, the hub
must pass it on as packets; however, if the incoming data is analog, then the hub passes it on in signal
form.

Hubs do not perform packet filtering or addressing functions; they just send data packets to all connected
devices. Hubs operate at the Physical layer of the Open Systems Interconnection (OSI) model. There are
two types of hubs: simple and multiple port.

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SWITCH:

Switches generally have a more intelligent role than hubs. A switch is a multiport device that improves
network efficiency. The switch maintains limited routing information about nodes in the internal network,
and it allows connections to systems like hubs or routers. Strands of LANs are usually connected using
switches. Generally, switches can read the hardware addresses of incoming packets to transmit them to the
appropriate destination.

Using switches improves network efficiency over hubs or routers because of the virtual circuit capability.
Switches also improve network security because the virtual circuits are more difficult to examine with
network monitors. You can think of a switch as a device that has some of the best capabilities of routers
and hubs combined. A switch can work at either the Data Link layer or the Network layer of the OSI
model. A multilayer switch is one that can operate at both layers, which means that it can operate as both a
switch and a router. A multilayer switch is a high-performance device that supports the same routing
protocols as routers.

Switches can be subject to distributed denial of service (DDoS) attacks; flood guards are used to prevent
malicious traffic from bringing the switch to a halt. Switch port security is important so be sure to secure
switches: Disable all unused ports and use DHCP snooping, ARP inspection and MAC address filtering.

ROUTER:

Routers help transmit packets to their destinations by charting a path through the sea of interconnected
networking devices using different network topologies. Routers are intelligent devices, and they store
information about the networks they’re connected to. Most routers can be configured to operate as
packetfiltering firewalls and use access control lists (ACLs). Routers, in conjunction with a channel service
unit/data service unit (CSU/DSU), are also used to translate from LAN framing to WAN framing. This is
needed because LANs and WANs use different network protocols. Such routers are known as border
routers. They serve as the outside connection of a LAN to a WAN, and they operate at the border of your
network.

Router are also used to divide internal networks into two or more subnetworks. Routers can also be
connected internally to other routers, creating zones that operate independently. Routers establish
communication by maintaining tables about destinations and local connections. A router contains
information about the systems connected to it and where to send requests if the destination isn’t known.

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Routers usually communicate routing and other information using one of three standard protocols: Routing
Information Protocol (RIP), Border Gateway Protocol (BGP) or Open Shortest Path First (OSPF).

Routers are our first line of defense, and they must be configured to pass only traffic that is authorized by
network administrators. The routes themselves can be configured as static or dynamic. If they are static,
they can only be configured manually and stay that way until changed. If they are dynamic, they learn of
other routers around them and use information about those routers to build their routing tables.

Routers are general-purpose devices that interconnect two or more heterogeneous networks. They are
usually dedicated to special-purpose computers, with separate input and output network interfaces for each
connected network. Because routers and gateways are the backbone of large computer networks like the
internet, they have special features that give them the flexibility and the ability to cope with varying
network addressing schemes and frame sizes through segmentation of big packets into smaller sizes that fit
the new network components. Each router interface has its own Address Resolution Protocol (ARP)
module, its own LAN address (network card address) and its own Internet Protocol (IP) address. The
router, with the help of a routing table, has knowledge of routes a packet could take from its source to its
destination. The routing table, like in the bridge and switch, grows dynamically. Upon receipt of a packet,
the router removes the packet headers and trailers and analyzes the IP header by determining the source
and destination addresses and data type, and noting the arrival time. It also updates the router table with
new addresses not already in the table. The IP header and arrival time information is entered in the routing
table. Routers normally work at the Network layer of the OSI model.

BRIDGE:

Bridges are used to connect two or more hosts or network segments together. The basic role of bridges in
network architecture is storing and forwarding frames between the different segments that the bridge
connects. They use hardware Media Access Control (MAC) addresses for transferring frames. By looking
at the MAC address of the devices connected to each segment, bridges can forward the data or block it
from crossing. Bridges can also be used to connect two physical LANs into a larger logical LAN.

Bridges work only at the Physical and Data Link layers of the OSI model. Bridges are used to divide larger
networks into smaller sections by sitting between two physical network segments and managing the flow
of data between the two.

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Bridges are like hubs in many respects, including the fact that they connect LAN components with
identical protocols. However, bridges filter incoming data packets, known as frames, for addresses before
they are forwarded. As it filters the data packets, the bridge makes no modifications to the format or
content of the incoming data. The bridge filters and forwards frames on the network with the help of a
dynamic bridge table. The bridge table, which is initially empty, maintains the LAN addresses for each
computer in the LAN and the addresses of each bridge interface that connects the LAN to other LANs.
Bridges, like hubs, can be either simple or multiple port.

Bridges have mostly fallen out of favor in recent years and have been replaced by switches, which offer
more functionality. In fact, switches are sometimes referred to as “multiport bridges” because of how they
operate.

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