Network Devices Comprehensive Notes
Network Devices
Objectives
Describe the basic operation of network repeaters and hubs
Explain the purpose of network switches
Summarize the operation of wireless access points
Describe the basic operation of network interface cards
Explain the function of routers
Network Repeaters and Hubs
Early networks didn’t use interconnecting devices.
This severely limited the total cable length (due to signal attenuation) and the number of computers.
Some problems were resolved with a device called a repeater.
A repeater receives bit signals generated by NICs and other devices, strengthens them, and then “repeats” them to other parts of the network.
A repeater enables you to connect computers whose distance from one another would make communication impossible.
A traditional repeater has two ports or connections that you can use to extend your network.
A multiport repeater is just a repeater with several ports to which you can connect cabling.
Also referred to as a hub.
Receives bit signals generated from a connected computer’s NIC on one of its ports.
Cleans the signal by filtering out electrical noise.
Regenerates the signal to full strength.
Transmits the regenerated signal to all other ports where a computer (or other network device) is connected to.
A repeater regenerates a signal, not amplify it.
In a hub, a frame is passed along or "broadcast" to every one of its ports, regardless of the intended destination. This leads to a lot of traffic on the network and can cause poor network response times.
Hubs and Network Bandwidth
Network bandwidth is the amount of data that can be transferred in an interval.
Usually measured in bits per second (bps), with networks operating at speeds from 10 million bps up to 10 gigabit per second (Gbps).
Hubs share bandwidth with all other connected computers.
Only one computer can successfully transmit data at a time.
Bandwidth sharing means all computers connected to the hub must share the amount of bandwidth the hub provides.
Hub Indicator Lights
Power, link status, network activity, collisions
Uplink port is a port used to connect two hubs together or a hub to a switch
Network Switches
Looks just like a hub but a switch actually reads data in the message, determines which port the destination device is connected to, and forwards the message to only that port
Basic Switch Operation
Data is sent onto the medium one frame at a time.
Each frame has the destination and source MAC addresses
Switch reads the addresses:
Use the source MAC address of frame to keep a record of which computer is on which port (switching table)
Forwards the frame to the port where the destination MAC can be found
Steps of switch operation
The switch receives a frame.
The switch reads the source and destination MAC addresses.
The switch looks up the destination MAC address in its switching table.
The switch forwards the frame to the port where the computer owning the MAC address is found.
The switching table is updated with the source MAC address and port information.
Switches and Network Bandwidth
Each port gets dedicated bandwidth instead of having to share bandwidth with all ports
Multiple conversations can occur simultaneously
Can operate in full-duplex mode (can send and receive data simultaneously)
Hubs can only operate in half-duplex mode (can send or receive, but not both at one time)
Switches are the preferred device because of these advantages
A switch keeps a record of the MAC (Media Access Control) addresses of all the devices connected to it.
With this information, a switch can identify which system is sitting on which port.
When a frame is received, it knows exactly which port to send it to, without significantly increasing network response times.
A 10/100Mbps switch will allocate a full 10/100Mbps to each of its ports.
So regardless of the number of PCs transmitting, users will always have access to the maximum amount of bandwidth.
Switch Indicator Lights
Like hubs, switches have indicator lights.
Switches have link status indicators and activity indicators
May also have indicators for whether the switch is operating in full-duplex or half-duplex mode
Switches can be connected to one another so that your LAN can grow beyond the limitations of ports on a single switch
Some switches have a dedicated port for uplinking to another switch
Wireless Access Points
The heart of a wireless network is the wireless access point (AP)
APs operate similarly to a hub without wires
All communication passes through the AP
Most small business and home networks use a device typically called a wireless router that combines the functions of an AP, a switch, and a router
Wireless LANs are usually attached to wired networks
Network Interface Cards
Most NICs are built into a computer’s motherboard
Occasionally fail or additional NICs are needed for an application
It is important to know how to install a new NIC
Attaching a computer to a network requires a network interface card (NIC) to create and mediate the connection between a computer and the networking medium.
Networking medium might be copper wire, fiber-optic cable, or airwaves
The tasks a NIC and its driver perform:
Provide a connection from computer to medium
Incoming messages: Receives bit signals and assembles them into frames
Verifies the destination address
Removes frame header and sends the resulting packet to the network protocol
Outgoing messages: receive packets from network protocol
Creates frames by adding MAC addresses/error check
Converts frame into bit signals suitable for the medium and transmits them
NICs and MAC Addresses
NIC manufacturers ensure that every NIC produced has a unique address
Networks won’t function correctly if duplicate MAC addresses exist
MAC address is stored in read-only memory (ROM) on the NIC
Two 24-bit hexadecimal numbers
24-bit manufacturer ID called OUI
24-bit serial number assigned by the manufacturer
48-bit address expressed in 12 hexadecimal digits: 04-40-31-5B-1A-C4
The NIC as Gatekeeper
When a frame arrives at a NIC, the NIC check’s the frame’s destination MAC address to see whether it matches it’s built-in MAC address
NIC only permits inbound communications if the destination MAC:
Matches the NICs burned-in address
Is a broadcast address (ff-ff-ff-ff-ff-ff)
NIC is in a special mode called promiscuous
When the destination MAC address matches the MAC burned-in address (BIA), or the physical address of a NIC, it’s a unicast frame
Intended for a single computer
When the destination is the broadcast address, it’s a broadcast frame
Broadcast frames are intended to be processed by all computers on the network
Promiscuous mode
turns off the gatekeeper functions and enables the NIC to process all frames it sees
Used by software called a protocol analyzer or packet sniffer
NIC Indicator Lights
NICs have indicator lights to show status information
Usually a link status indicator and an activity indicator
The link light is usually green when the NIC has a valid connection to the network medium
Some NICs support multiple speeds
There is usually a separate light for each speed so that you can determine at what speed the NIC is connected to the hub or switch
In other cases, the light is a different color for each speed, such as amber for 100 Mbps and green for 1000 Mbps
Selecting a NIC
NICs are often built into motherboard
However, an additional NIC or a faster NIC may need to be installed
When selecting a NIC you need to select correct bus interface
The connection the NIC makes to the motherboard is the bus connection
The NIC driver (software) must be available for your OS
Desktop NICs versus server NICs
For desktops, a standard NIC is good enough
For servers, consider a NIC with onboard memory, multiple ports and performs faster
NIC Drivers
Most OSs ship with drivers for wide range of NICs
Most NICs include drivers for the most common OSs
In most cases, you only need to install the NIC and restart your computer
If the OS has a suitable driver available it is installed automatically
After installation, Windows 8.1 and later shows your installed NIC as a Network Connection
In Windows, each connection is assigned a name which you can rename
Wireless NICs
Wireless NICs must be chosen according to the type of wireless AP being used
Typical are Wireless-n, 802.11ac or 802.11 a/b/g/n
The letters a,b,g, n, and ac refer to the wireless networking standard the device supports
Wireless NICs connect to network using service set identifier (SSID)
SSID is the name assigned to the wireless network
You may also need to enter a security key or a username and password, depending on the network’s security configuration
Wireless LAN Standards
Beside the speed and frequency band, other differences are:
Number of channels
Cell size (coverage area)
Routers
Most complex device
Connect LANs together to create an internetwork (Network of Networks)
Routers are devices that enable multiple LANs to communicate with one another by forwarding packets from one LAN to another
The following are the differences between routers and switches
Routers connect LANs, switches connect computers to form LANs
Routers work with logical (IP) addresses, switches work with physical (MAC) addresses
Routers work with packets, switches with frames
Routers don’t forward broadcasts, switches do
Routers use routing tables, switches use switching tables
Routers Connect LANs
As computers are added to a LAN, effective communication can suffer
Broadcast traffic is forwarded to all members of a LAN and can cause a network to become congested
The administrator groups users and servers together based on their department or function
The router is used to connect 3 separate LANs in order to contain broadcast traffic and facilitate more effective communication in each department LAN
Between each Router, the MAC address header is stripped and regenerated to get it to the next hop.
The IP header generated by the first computer is only stripped off by the final computer, hence the IP header handled the “end to end” delivery, and each of the four different MAC headers involved in this animation handled the “hop to hop” delivery.
CIDR IP address (revision)
RESERVED IP ADDRESS 192.168.1.0 subnet
192.168.1.255 broadcast
Total usable hosts
Online tools subnetmask: 11111111 11111111 11111111 00000000
CIDR Range
192.168.1.0/23
Netmask 255.255.254.0
Wildcard Bits 0.0.1.255
First IP 192.168.0.0
Last IP 192.168.1.255
Total Host 512
Result usable hosts:
Subnet mask: 11111111 11111111 11111110 00000000
SPStudent network
CIDR Range 172.22.20.159/21
Netmask 255.255.248.0
Wildcard Bits 0.0.7.255
First IP 172.22.16.0
Last IP 172.22.23.255
Total Host 2048
CIDR subnetmask: 11111111 11111111 11111000 00000000
Usable hosts:
LAN - Privated IP address
Reserved for private networks. The organizations that distribute IP addresses to the world reserves a range of IP addresses for private networks.
192.168.0.0 - 192.168.255.255 (65,536 IP addresses)
172.16.0.0 - 172.31.255.255 (1,048,576 IP addresses)
10.0.0.0 - 10.255.255.255 (16,777,216 IP addresses)
Private IP address for LAN
Public IP Address for router
The two work together as a team.
Both IPs are needed so that when you go to Amazon.com, the Internet knows to send the information you request back to your computer and not someone else's (including not someone else in your home, using the same network).
The go-between for the public and non-public IP address is your router:
Your router has assigned to your computer an internal IP address, to which you're connected wirelessly or directly. (It also assigns a different, but similar internal IP address to any other computer connected on your network.)
Your router