Networking Devices
Lecture-5
Computer Network & Communication (I)
Contents
• Common Network Connectivity Devices
• Other Specialized Devices
Common Network Devices
Here’s a list of the devices we’ll be covering in this chapter:
• Hub
• Network Interface Card (NIC)
• Bridge
• Basic switch
• Basic router
• Basic firewall
• Basic Dynamic Host Configuration Protocol (DHCP) server
• Other specialized devices
Network Interface Card (NIC)
• Those of you who aren’t familiar with NICs probably want to be, at this point, so here goes: a Network
Interface Card (NIC) is installed in your computer to connect, or interface, your computer to the
network.
• It provides the physical, electrical, and electronic connections to the network media.
• A NIC either is an expansion card or is built right into the computer’s motherboard.
• The NIC usually connects to the computer through expansion slots located on the motherboard that
allow peripherals to be plugged in directly.
• In some notebook computers, NIC adapters can be connected to the printer port or through a PC card
slot.
Network Interface Card (NIC)
Network Interface Card (NIC)
• As a hub has no intelligence, it is a Layer 1 device.
• Any transmission received on one port will be sent out to all the
other ports in the hub, including the receiving pair for the
transmitting device, so that Carrier Sense Multiple Access with
Collision Detection (CSMA/CD) on the transmitter can monitor
for collisions. So, basically, this means that if one station sends a A typical hub
broadcast, all the others will receive it. Figure 5.2
• Since there are only two users, there isn’t a problem in using a
hub here. However, if there were 20 users, everyone would see
Bob’s request to send a packet to Sally. Most of the time, hubs
really aren’t recommended for corporate networks because of
their limitations.
A Basic Hub
As you learned earlier, a hub is the device that
connects all the segments of the network
together in a star topology Ethernet network.
Every device in the network connects directly to
the hub through a single cable and is used to
connect multiple devices without segmenting a
network.
Bridge
Collision domains
Bridge
One broadcast domain
A bridge—specifically, a transparent bridge—is a network device that connects two similar network
segments together. Its primary function is to keep traffic separated on either side of the bridge, breaking
up collision domains.
As bridges use MAC addresses to make forwarding decisions, they are considered Layer 2 devices.
Switch
• Switches connect multiple segments of a
network together much like hubs do, but with
three significant differences—a switch
recognizes frames and pays attention to the
source and destination MAC address of the
incoming frame as well as the port on which it
was received.
Internet
Router Wireless
Router
Computer
equipped with
DSL/Cable network adapter
Modem
• A router is a network device used
to connect many, sometimes
disparate, network segments
together, combining them into
what we call an internetwork .
Computer
• As routers use IP addresses to make equipped with
wireless adapter
Notebook
equipped with
forwarding decisions, they are Wireless adapter
considered Layer 3 devices
Interface Configurations
Router(config-if)#ip address 1.1.1.1 255.0.0.0
Router(config-if)#no shutdown
Router(config-if)#
*Oct 5 17:26:46.522: %LINK-3-UPDOWN: Interface
FastEthernet0/0, changed state
to up
*Oct 5 17:26:47.522: %LINEPROTO-5-UPDOWN: Line
protocol on Interface
FastEthernet0/0, changed state to up
Firewall
• Basically, firewalls are your network’s security guards; and to be real, they’re probably
the most important thing to implement on your network.
• That’s because today’s networks are almost always connected to the Internet—a
situation that makes security crucial!
• A firewall protects your LAN resources from invaders that prowl the Internet for
unprotected networks, while simultaneously preventing all or some of your LAN’s
computers from accessing certain services on the Internet.
• You can employ them to filter packets based on rules that you or the network
administrator create and configure to strictly delimit the type of information allowed
to flow in and out of the network’s Internet connection.
Firewall
Internet
Internal Network
Firewall Firewall
DMZ
• Sometimes, there is a second firewall, as shown in Figure 5.6. This firewall is used to
connect servers and equipment that can be considered both public and private (like
web and email servers). This intermediary network is known as a demilitarized zone
(DMZ).
Access Point Internet
Wireless
Router
DSL/Cable
Modem
• an AP is just a hub that accepts wireless clients via an analog wireless
signal. APs operate at Layer 2.
• Figure shows how an AP would look in a small network, such as a
home.
DHCP Dynamic Host Configuration Protocol Server
• In essence, DHCP servers assign IP addresses to hosts. This protocol gives us a much
easier way to administrate—by automatically providing IP information—than the
alternative and tedious method known as static IP addressing, where we have to
address each host manually.
• It works well in any network environment, from tiny to huge, and allows all types of
hardware to be employed as a DHCP server, including routers.
• A DHCP server receives request for IP information from a DHCP client using a
broadcast. The only hitch is that if the DHCP server isn’t on the same segment as the
DHCP client, the broadcast won’t be received by the server because by default, routers
won’t forward broadcasts.
DHCP Client
• Shown in the figure on the next slide, Router A is configured with the IP helper address
command on interface E0 of the router. Whenever interface E0 receives a broadcast
request, Router A will forward those requests as a unicast (meaning instead of a
broadcast, the packet now has the destination IP address of the DHCP server).
• You can configure Router A to forward these requests and even use multiple DHCP
servers for redundancy, if needed. This works because the router has been configured
to forward the request to a single server using a unicast or by sending the request to
multiple servers via a directed broadcast.
DHCP Client
Single-Server Example
A B
Unicast
Client
Server
Broadcast
Multiple-Server Example
A B
Directed
Broadcast
Client Server Server
Broadcast
DHCP Server Options
• Scope Options provide IP configuration for hosts on a specific subnet. Below the Scope
Options, you’ll find Server Options, which provide IP information for all scopes
configured on the server.
• If I had just one Domain Name Service (DNS) server for the entire network, I’d
configure the Server Options with my DNS server information; that DNS server
information would then show up automatically in all scopes configured on my sever.
DHCP Server Options
DHCP Client Request
• So, what exactly does a DHCP client ask for, and what does a DHCP server provide?
Is it just an IP address, a mask, and a default gateway? Let’s take a look at a DHCP
client request on an analyzer on the next slide.
DHCP Client Request
DHCP Server Response
DHCP Relay
• If you need to provide addresses from a
DHCP server to hosts that aren’t on the
same LAN as the DHCP server, you can
configure your router interface to relay or
forward the DHCP client requests, as
shown in Figure.
Specialized Devices
• Multilayer switch
• Content filter
• Load balancer
• DNS server
• Proxy server
• Encryption devices
• VPN Concentrator
Multilayer Switch
• A multilayer switch (MLS) is a computer networking device that switches on Open
Systems Interconnection (OSI) Layer 2 like an ordinary network switch but provides
extra functions on higher OSI Layers, like Layer 3, for routing .
• A layer 3 switch (multilayer switch) can also be called a router, and vice versa.
• A 24-port MLS gives you the best of both worlds. It operates at Layer 3 (routing)
while still providing 24 collision domains, which a router could not do.
Domain Name Service (DNS)
• A Domain Name Service (DNS) server is one of the most important servers in your
network and on the Internet as well.
• A host name is typically the name of a device that has a specific IP address; on the
Internet, it is part of what is known as a fully qualified domain name (FQDN). An
FQDN consists of a host name and a domain name.
• Your local ISP is probably a member of the .net domain, and your company is
probably part of the .com domain. The .gov and .mil domains are reserved strictly
for use by the government and the military within the United States.
DNS Resolution Example
DNS Server Config
Host (A) is called an A record
and is what gives you the IP
address of a domain or host.
Mail Exchanger (MX)
• Here are some sample mail-exchange records:
hostname.company.com. IN MX 10 mail.company.com
hostname.company.com. IN MX 20 mail2.company.com
hostname.company.com. IN MX 30 mail3.company.com
• In this example, if the first mail exchanger, mail.company.com, does not respond,
the second one, mail2.company.com, is tried, and so on.
A DNS query to www.lammle.com
Figure 5.16
The DNS answer to our query
Figure 5.17
Dynamic DNS
• Hosts register their names with the DNS sever as they receive their IP address
configuration from the DHCP server.
• Some of the record types we have discussed can only be created manually. These
include MX and CNAME records.
PC
Proxy Server LAN
Proxy
Server Router Second
• A proxy server is basically a type of server Switch PC or Printer
that handles its client-machine requests by
forwarding them on to other servers while Internet
allowing granular control over the traffic
between the local LAN and the Internet.
• Sometimes the proxy modifies the client’s
request or a server’s response to it—or
even handles the client’s request itself.
• Figure shows where a proxy server would Wireless
be typically found in a small-to-medium Connection
network.
Encryption Devices
• The advantage of using these devices is that they normally
provide more choice of encryption methods and stronger
encryption options.
• Sometimes these devices are called encryption gateways.
They can either sit in line with a server or a local network,
encrypting and decrypting all traffic, or function as an
application server, encrypting any file sent to them within
a network.
Encryption Devices
Content filtering appliance
Figure 5.20
• Email is a good example of what you might run through one of these devices to filter out spam and
objectionable content before the email is delivered. Another example of the use of a content filter
might be to block websites based on the content of the web pages rather than on the basis of the
URL or IP address.
• An example of a dedicated content/URL filtering appliance from SecPoint is shown in Figure
Analog Modem
• A modem (modulator-demodulator) is a device that modulates an
analog carrier signal to encode digital information and demodulates
the signal to decode the transmitted information.
• The goal is to produce a signal that can be transmitted easily and
decoded to reproduce the original digital data. These signals are
transmitted over telephone lines and demodulated by another
modem at the receiver side in order to read the digital data.
Packet Shaper
• Packet shaping (also known as traffic shaping, it’s a form of rate limiting) is an Internetworking
traffic management technique that delays some or all packets to bring them into compliance with
your or your company’s traffic profile. Figure shows a dedicated packet shaper appliance from Blue
Coat.
• This process is used to optimize or guarantee performance, improve latency, and/or increase
usable bandwidth for some kinds of packets by delaying other kinds, decided on by you.
VPN Concentrator
• VPN concentrator is a device that accepts multiple
VPN connections from remote locations.
• Although this function can be performed by a
router or server, as with the encryption gateways
and content filtering devices discussed earlier, the
same performance benefits can be derived from
dedicating a device to this. Moreover, additional
functionality usually comes with these devices,
one of which is shown in Figure.
Planning and Implementing a Basic SOHO Network Using Network
Segmentation
Issues driving requirements
• Too many hosts in a broadcast domain
• Broadcast storms
• Multicasting
• Low bandwidth
• Adding hubs for connectivity to the network
Here’s a list of some of the things that commonly cause
LAN traffic congestion:
• Too many hosts in a broadcast domain
• Broadcast storms
• Multicasting
• Low bandwidth
• Adding hubs for connectivity to the network
A switch can replace the hub, breaking up collision domains.
Switch
Hub
Routers create an internetwork.
There are two advantages of using routers in your
network:
• They don’t forward broadcasts by default.
• They can filter the network based on Layer 3
(network layer) information (such as an IP
address).
Four router functions in your network can be listed
as follows: Switch
Serial 0
• Packet switching
• Packet filtering
• Internetwork communication
• Path selection
Switch
Internetworking devices
Bridge
Switch Router
Switched networks creating an internetwork
Router
A router in an internetwork
FastEthernet0/0 Serial0
Internet
WAN Services
FastEthernet0/1
A switch in an internetwork
1 2 3 4
Each segment has its own collision domain.
All segments are in the same broadcast domain.
A hub in a network
A B C D
All devices in the same collision domain
All devices in the same broadcast domain
Devices share the same bandwidth
Reference
• CompTIA-Network-Study-Guide-Exam-N10-007
• Layer 2 vs Layer 3 Switches (youtube.com)
