Network Terms and Introduction to Network

What is meant by the terms Network here includes both physical and virtual terms. A physical switch or a network layer represents a virtual network. Therefore, let’s try to understand Network Architecture under two different headings as physical and virtual.

There are hundreds of different brands and models of network devices. Firewall, Switch, Farm Switch, Router, Server, Modem, Network Card, Computer, Smart Phones, IoT (end units working with io technology), wearable technology tools, smart home appliances (washing machine, boiler, airfryer, robot vacuum cleaner) fiber optic cables, coaxial cables, cabinets and even the human being himself is an element of this network as a user.

Although brands and models may differ, the language they use must be the same. Otherwise, network devices of different brands and models cannot communicate with each other and as a result, network communication cannot be achieved and there is no point in learning network terms.

I can recommend Udemy Online Academy courses for those who want to improve themselves in networking. It brings you to a certain point. Then it’s up to you to make the leap.

Network Modelleri

In this article on network terms, we will start by talking about Network Models, which have developed perhaps a little bit as a chronological process. Models are named according to the references they take.

TCP/IP Based Model

It is a very old but reliable model used in the discovery of network systems. It works on the basis of transporting data packets with IP addressing. Today, this method is actively preferred in Local Area Network (Local Area Network) and Wide Area Network (in short, Internet) environments.

Layers work in the same way as the working logic of the Layers in the OSI Model. There is communication between Upper and Lower Layers.

OSI Referans Modeli

The OSI Model, known as Open System Interconnection, consists of a total of 7 layers. These layers are

Fortigate ile Whatsapp Engelleme

Each layer works independently of each other. However, if desired, these layers can communicate with the layers above and below.

Application Layer (Layer 7 – Application)

As the name implies, certain applications run over protocols at this layer. Protocols such as Http, Ftp, Tftp, Smtp, Pop3, Rstp, Dhcp, Dns, Tcp, Udp.

Presentation Layer (Layer 6 – Presentation)

Prepares and presents data to the application layer, the next layer up. Transmits data packets to the Application Layer in the expected formats.

Session Layer (Layer 5 – Session)

It establishes and manages sessions to establish connections between sending and receiving terminals.

Transport Layer (Layer 4 – Transport)

This layer is responsible for transporting, fragmenting and combining data packets.

Network Layer (Layer 3 – Network)

Defining Ip addresses for users and devices, communicating with the user by going to the destination in the most accurate, reliable and fastest way is provided in the Network Layer. Communication between different networks is also done through the Layer 3 layer.

Data Link (Layer 2 – Data Link)

It converts the data coming from the Network Layer into frames of 1s and 0s and transmits them to the lower layer, Layer1.

Physical Layer (Layer 1 – Physical)

Between the sender and the receiver, i.e. the server and the user, it receives the incoming data over the physical cable etc. and transmits it to the upper layer.

TCP/IP and OSI Comparison

Network Types

It is a network topology that is shaped according to the requirements. It is specially selected and designed for an office, for a company or for branches of the company in different locations (it can be anywhere in the world).

LAN – Local Area Network (Yerel Ağ)

It is the most suitable network type for use in a small area. It is suitable for use in offices in a building or several buildings side by side. LAN can also be used at long distances with VPN, Virtual Private Network, which we will see in the future. We will address this issue in the future.

There are different network terms for Local Area Network. For example

SOHO LAN

More often in our homes or small businesses, Computers, Laptops, Smart Devices, Printers and Scanners communicate with a simple Router on the Modem device on this network. It is designed in plug and play logic so that users at all levels can use it easily. Let’s also note the Soho type Lan model as a new Network term.

Local Area Network (LAN) Elements

All elements that can access the network by obtaining an IP address physically or virtually can be considered as a network device.

• Router
• Firewall
• Switch
• Access Point (WiFi Devices)
• Computers
• Printer / Scanner
• Server
• Tablet
• Mobile Phone
• IoT Devices (boiler, washing machine, robot vacuum cleaner, air conditioner etc.)

The network element connected to the switch via an ethernet interface operates in full-duplex (bidirectional send/receive at the same time). However, in hub (dumb switch) devices, it only works in half-duplex mode, that is, only send or receive at the same time.

Cisco Packet Tracer Download

Switch

It can be said that the basis of the network system is Switches. Switches are the first place where network devices with ethernet interface meet the network.

• Number of ports,
• Port speeds,
• Cpu capability,
• Security,
• PoE (Power of Ethernet) power support
• Up-time standards
• and of course you can buy a Switch by evaluating parameters such as Cost. If you are building a network from scratch, these parameters will be very decisive for you.

Many brands such as Cisco, HP, Procurve, Extreme, Juniper, Huawei, Alcatel, TpLink have proven themselves in this field. They can also work very stably with each other.

Network Communication System (IOS)

It is the common language that allows network elements to communicate with each other, regardless of brand, model or type. Let’s not confuse it with Apple ios. It provides components such as network security, IP addressing, Routing, QoS standard.

The CLI console screen has several different input types for IOS configuration.

1. Standard User Mode
2. Authorized User Mode
3. Global Settings Mode
4. Interface Configuration Mode

Switch> enable
Switch# config terminal
Switch (config)# interface gigabitEthernet0/1/0

In the CLI Console screen above, the lines are respectively:

Line 1: Type“enable” to enter authorized mode.
Line 2: Type“config terminal” or abbreviated“conf t” to enter global configuration mode.
Line 3: Type“interface port_name” or“int port_name” for short to enter interface mode for a port or interface settings.

CLI console entry modes on router devices can be done in a similar way.

Command Line Help

To see all the commands you can run on the CLI console screen, just type “?” and enter. If you want to get help about a command, you should type“command ?“.

You can exit the mode you activated with “disable” by typing“disable“. The“exit” command is usually used to exit modes. Let’s see in the example:

Switch> enable
Switch# ?
Exec commands:
  clear       Reset functions
  clock       Manage the system clock
  configure   Enter configuration mode
  connect     Open a terminal connection
  copy        Copy from one file to another
  debug       Debugging functions (see also 'undebug')
  delete      Delete a file
  dir         List files on a filesystem
  disable     Turn off privileged commands
  disconnect  Disconnect an existing network connection
  enable      Turn on privileged commands
  erase       Erase a filesystem
  exit        Exit from the EXEC
  logout      Exit from the EXEC
  more        Display the contents of a file
  no          Disable debugging informations
  ping        Send echo messages
  reload      Halt and perform a cold restart
  resume      Resume an active network connection
  setup       Run the SETUP command facility
  show        Show running system information
  
  
  
  Switch# show ?
  aaa                Show AAA values
  access-lists       List access lists
  arp                Arp table
  boot               show boot attributes
  cdp                CDP information
  clock              Display the system clock
  crypto             Encryption module
  dhcp               Dynamic Host Configuration Protocol status
  dtp                DTP information
  etherchannel       EtherChannel information
  flash:             display information about flash: file system
  history            Display the session command history
  hosts              IP domain-name, lookup style, nameservers, and host table
  interfaces         Interface status and configuration
  ip                 IP information
  lldp               LLDP information
  logging            Show the contents of logging buffers
  mac                MAC configuration
  mac-address-table  MAC forwarding table
  mls                Show MultiLayer Switching information
  monitor            SPAN information and configuration
  ntp                Network time protocol
  
  Switch# disable
  Switch>

Reload (Restart)

When you run the“reload” command on the CLI console screen while the Switch is in enable mode, the Switch or Router device is restarted.

Switch Configuration Saving Process

There are 3 different memory types in devices such as Switch and Router.

• NVRAM: Initial Configuration
• RAM: Running Configuration
• FLASH: IOS platform and backup files

If the configuration and changes you make on the Switch or Router are not saved in non-volatile memory, they will be deleted when the device is turned off. For this, it is enough to type“write memory” or its abbreviation“wr mem” in enable mode when the configuration process is finished.

Switch# write memory 
Building configuration...
[OK]

To save the running configuration as a startup configuration, type the following command line:

Switch# copy running-config startup-config 
Destination filename [startup-config]? 
Building configuration...
[OK]

To return to the Initial Configuration, you can do the opposite of the above process:

Switch# copy startup-config running-config
Destination filename [running-config]? 
Building configuration...
[OK]

Switch and Router Startup Configuration Commands

Let’s make initial settings on a switch or router that you have just installed and has not yet been configured.

Switch Hostname Ayarı

You can change the switch name with the“hostname device_name” command in config mode.

Switch# config t
Switch (config)# hostname SW1
SW1 (config)#

Escape Tab on Incorrect Command Entry

When you type an incorrect command on the console screen, the switch recognizes it as a device name in the network and starts searching for it. This takes about 1 minute. If you do not want to wait for this time, you can create an escape tab with the“Ctrl+Shift+6” key combination or the“Break” key and exit.

If you want to turn it off completely, run the following command in the CLI:

SWW1 (config)# no ip domain-lookup

Debugging Cisco CLI Console

There are 3 different types of errors returned for incorrect entries made on routers or switches.

1. Ambiguous Command Input

When you type an ambiguous command on the command line, it cannot parse it and returns“% Ambiguous Command: “.

SWW1# cl ?
% Ambiguous command: "cl "

2. Incomplate Command

The type of error returned for a command with a missing parameter on the command line.

SWW1# clock
% Incomplete command.

3. Flagged Bad Command

Indication of an incorrect command or parameter section by marking it with a “^” marker.

SWW1#clock set 10:39:00 21 02
                           ^
% Invalid input detected at '^' marker.

Time Setting on Switch and Router Devices

Let’s try setting the date and time in the above example.

SWW1# clock set 10:39:00 27 Feb 2025

SWW1# wr mem

Now that we have a lot of technical knowledge about network terms, the next step will be to communicate these devices with each other and ensure their stable operation.

IP Adrressing

Every network device must have an IP and Mac Address to be able to access the network. Otherwise routers, switches or firewall devices will not be able to detect you. Anyone who uses a modem to connect to the internet at home knows what an IP address looks like.

You may have seen IP addresses assigned to your modem by an ISP, such as 192.168.1.1 for simple networks, 10.14.10.1 for specially configured networks, or 43.81.30.148.

The IP address given in the table above is a 32 Bit C-class IP address. IP addresses are perhaps one of the most basic and important definitions in the dictionary of network terms.

How to Convert IP Address Decimal to Binary?

Conversion of 192 to Decimal:

Decimal Conversion of Number 10:

IP Address Classes

Ip addresses are grouped into 5 different classes. This network term is very important in network designs. Because it can be very difficult to change later. When designing the network architecture, it should be decided very wisely which class of Ip addressing to use.

General Purpose (Public IP Addresses)

• Class-A IP Addresses: 1.0.0.0 – 126.255.255.255
• Class-B IP Addresses: 128.0.0.0 – 191.255.255.255
• Class-C IP Addresses: 192.0.0.0 – 223.255.255.255

Special Purpose (Private IP Addresses)

• Class-A IP Addresses: 10.0.0.0 – 10.255.255.255
• Class-B IP Addresses: 172.16.0.0 – 172.31.255.255
• Class-C IP Addresses: 192.168.0.0 – 192.168.255.255

DNS – Domain Name System

Domain Name is actually a network term that almost everyone knows today.

For example, when you type https://www.cisco.com into your web browser, the following happens in the background:

1. A Domain Name (Domain Name:https://www.cisco.com) is sent to your DNS server and a request is made for IP address resolution. IP resolution was performed on the DNS server of the ISP (Internet Service Provider) you use.
2. A request was sent to the ip address 72.247.161.58, i.e. Cisco’s web server.
3. Cisco trusted this connection and responded positively to your request, allowing the site’s index page to load.

To see all these DNS redirects, you can use the following codes by going to the Command Prompt or Terminal screen.

• Windows CMD: tracert cisco.com
• Apple/Linux: traceroute cisco.com

Screen Output:

omersahin@Omer-iMac ~ % traceroute cisco.com

 1  192.168.1.1 (192.168.1.1)  1.496 ms  1.159 ms  1.686 ms
 2  172.17.1.207 (172.17.1.207)  5.379 ms  5.201 ms  5.298 ms
 3  159.146.113.153.gigafiber.turk.net (159.146.113.153)  7.498 ms  8.738 ms  8.045 ms
 4  95.70.250.162.gigafiber.turk.net (95.70.250.162)  6.203 ms  5.713 ms  5.302 ms
 5  * * *
 6  198.92.146.159.srv.turk.net (159.146.92.198)  8.470 ms * *
 7  206.105.192.193.static.turk.net (193.192.105.206)  7.667 ms  6.494 ms  6.327 ms
 8  93.186.132.164 (93.186.132.164)  46.618 ms  44.034 ms  50.257 ms
 9  89.221.34.251 (89.221.34.251)  60.364 ms  52.205 ms
    195.22.211.61 (195.22.211.61)  45.555 ms
10  89.221.34.189 (89.221.34.189)  43.159 ms  46.421 ms
    ae16.edge8.frf1.sp.lumen.tech (4.68.63.109)  58.046 ms
11  ae3.5.edge5.dallas3.net.lumen.tech (4.69.208.229)  159.260 ms  158.768 ms  159.652 ms
12  cisco-syste.edge5.dallas3.level3.net (4.59.34.66)  163.577 ms  160.763 ms  166.273 ms
13  128.107.2.5 (128.107.2.5)  160.533 ms  163.540 ms  159.833 ms
14  72.163.0.102 (72.163.0.102)  160.392 ms  165.538 ms
    72.163.0.98 (72.163.0.98)  165.557 ms
15  rcdn9-cd2-dmzdcc-gw2-por1.cisco.com (72.163.0.182)  160.113 ms  164.312 ms
    rcdn9-cd1-dmzdcc-gw1-por1.cisco.com (72.163.0.178)  159.758 ms
16  rcdn9-br07-fab1-sw3812-dmzdcc1uplink.cisco.com (72.163.2.206)  163.928 ms
    rcdn9-bb07-fab1-sw3811-dmzdcc2uplink.cisco.com (72.163.3.2)  160.047 ms
    rcdn9-br07-fab1-sw3812-dmzdcc2uplink.cisco.com (72.163.3.6)  160.316 ms

• nslookup www.cisco.com

Screen Output:

omersahin@Omer-iMac ~ % nslookup www.cisco.com
Server:		8.8.8.8
Address:	8.8.8.8#53

Non-authoritative answer:
www.cisco.com	canonical name = www.cisco.com.akadns.net.
www.cisco.com.akadns.net	canonical name = wwwds.cisco.com.edgekey.net.
wwwds.cisco.com.edgekey.net	canonical name = wwwds.cisco.com.edgekey.net.globalredir.akadns.net.
wwwds.cisco.com.edgekey.net.globalredir.akadns.net	canonical name = e2867.dsca.akamaiedge.net.
Name:	e2867.dsca.akamaiedge.net
Address: 72.247.161.58

• ipconfig/displaydns | more

This command lists all dns resolutions defined on the computer.

IP Config Command in Apple and Linux

omersahin@Omer-iMac ~ % ifconfig
lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 16384
	options=1203<RXCSUM,TXCSUM,TXSTATUS,SW_TIMESTAMP>
	inet 127.0.0.1 netmask 0xff000000 
	inet6 ::1 prefixlen 128 
	inet6 fe80::1%lo0 prefixlen 64 scopeid 0x1 
	nd6 options=201<PERFORMNUD,DAD>
gif0: flags=8010<POINTOPOINT,MULTICAST> mtu 1280
stf0: flags=0<> mtu 1280
en0: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
	options=50b<RXCSUM,TXCSUM,VLAN_HWTAGGING,AV,CHANNEL_IO>
	ether 78:7b:8a:d6:ac:c1 
	nd6 options=201<PERFORMNUD,DAD>
	media: autoselect (none)
	status: inactive
en1: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
	options=400<CHANNEL_IO>
	ether 24:f6:77:18:1e:4a 
	inet6 fe80::d3:f82a:5998:71bb%en1 prefixlen 64 secured scopeid 0x5 
	inet6 2a02:ff0:22c:8086:97:c866:d211:6638 prefixlen 64 autoconf secured 
	inet6 2a02:ff0:22c:8086:5f3:29da:b33d:a94f prefixlen 64 autoconf temporary 
	inet 192.168.1.100 netmask 0xffffff00 broadcast 192.168.1.255
	nd6 options=201<PERFORMNUD,DAD>
	media: autoselect
	status: active
awdl0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1484
	options=400<CHANNEL_IO>
	ether ae:db:4b:1f:31:d5 
	inet6 fe80::acdb:4bff:fe1f:31d5%awdl0 prefixlen 64 scopeid 0x6 
	nd6 options=201<PERFORMNUD,DAD>
	media: autoselect
	status: active
llw0: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
	options=400<CHANNEL_IO>
	ether ae:db:4b:1f:31:d5 
	inet6 fe80::acdb:4bff:fe1f:31d5%llw0 prefixlen 64 scopeid 0x7 
	nd6 options=201<PERFORMNUD,DAD>
	media: autoselect
	status: active
en3: flags=8963<UP,BROADCAST,SMART,RUNNING,PROMISC,SIMPLEX,MULTICAST> mtu 1500
	options=460<TSO4,TSO6,CHANNEL_IO>
	ether 82:87:ab:67:d8:01 
	media: autoselect <full-duplex>
	status: inactive
en2: flags=8963<UP,BROADCAST,SMART,RUNNING,PROMISC,SIMPLEX,MULTICAST> mtu 1500
	options=460<TSO4,TSO6,CHANNEL_IO>
	ether 82:87:ab:67:d8:00 
	media: autoselect <full-duplex>
	status: inactive
bridge0: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
	options=63<RXCSUM,TXCSUM,TSO4,TSO6>
	ether 82:87:ab:67:d8:00 
	Configuration:
		id 0:0:0:0:0:0 priority 0 hellotime 0 fwddelay 0
		maxage 0 holdcnt 0 proto stp maxaddr 100 timeout 1200
		root id 0:0:0:0:0:0 priority 0 ifcost 0 port 0
		ipfilter disabled flags 0x0
	member: en2 flags=3<LEARNING,DISCOVER>
	        ifmaxaddr 0 port 9 priority 0 path cost 0
	member: en3 flags=3<LEARNING,DISCOVER>
	        ifmaxaddr 0 port 8 priority 0 path cost 0
	nd6 options=201<PERFORMNUD,DAD>
	media: <unknown type>
	status: inactive
utun0: flags=8051<UP,POINTOPOINT,RUNNING,MULTICAST> mtu 1380
	inet6 fe80::9183:7322:324:3e23%utun0 prefixlen 64 scopeid 0xb 
	nd6 options=201<PERFORMNUD,DAD>
utun1: flags=8051<UP,POINTOPOINT,RUNNING,MULTICAST> mtu 2000
	inet6 fe80::bf23:2299:4a7e:d267%utun1 prefixlen 64 scopeid 0xc 
	nd6 options=201<PERFORMNUD,DAD>
utun2: flags=8051<UP,POINTOPOINT,RUNNING,MULTICAST> mtu 1000
	inet6 fe80::ce81:b1c:bd2c:69e%utun2 prefixlen 64 scopeid 0xd 
	nd6 options=201<PERFORMNUD,DAD>
utun3: flags=8051<UP,POINTOPOINT,RUNNING,MULTICAST> mtu 1380
	inet6 fe80::5f10:f4e3:2b58:3317%utun3 prefixlen 64 scopeid 0xe 
	nd6 options=201<PERFORMNUD,DAD>
utun4: flags=8051<UP,POINTOPOINT,RUNNING,MULTICAST> mtu 1380
	inet6 fe80::7cd6:beb7:897c:f89d%utun4 prefixlen 64 scopeid 0xf 
	nd6 options=201<PERFORMNUD,DAD>

Subnets

In a network with many devices, a subnet can be defined to reduce the traffic caused by all broadcast and multicast messages.

Let’s create a subnet from this network.

Subnet Calculation

2 To Create Subnet (255.255.255.255.128)

2^a = 2^1 = 2 subnets
2^k = 2^7 = 128 blocks
(2^k)-2 = (2^7) – 2 = 128-2 = 126

In this case, IP Blocks will be as follows:

1. Subnet 192.168.1.0 network
   192.168.1.1 First IP
   192.168.1.126 Last IP
   192.168.1.127 Broadcast
2. Subnet 192.168.1.128 network
   192.168.1.129 First IP
   192.168.1.254 Last IP
   192.168.1.255 Broadcast

4 To Create Subnet (255.255.255.255.192)

2^a = 2^2 = 4 subnets
2^k = 2^6 = 64 blocks
(2^k)-2 = (2^6) – 2 = 64-2 = 62

In this case, IP Blocks will be as follows:

1. Subnet 192.168.1.0 network
   192.168.1.1 First IP
   192.168.1.62 Last IP
   192.168.1.63 Broadcast
2. Subnet 192.168.1.64 network
   192.168.1.65 First IP
   192.168.1.126 Last IP
   192.168.1.127 Broadcast
3. Subnet 192.168.1.128 Network
   192.168.1.129 First IP
   192.168.1.190 Last IP
   192.168.1.191 Broadcast
4. Subnet 192.168.1.192 network
   192.168.1.193 first IP
   192.168.1.254 last IP
   192.168.1.255 Broadcast

Python Application that Autowrites Subnet Configuration:
https://github.com/omersahintr/network/tree/main/SubnetCalculator

Subnet Calculator App:

The Easy Way to Calculate Subnet

Between 192.168.2.0 – 192.168.2.255 there are 256 ip in total.

To Divide the Network in Half:

Block = 256 / 2 = 128
Subnet = 256-128 = 128
Host = 128-2 = 126

1. Subnet 192.168.2.0 network
   192.168.2.1 First IP
   192.168.2.126 Last IP
   192.168.2.127 Broadcast
2. Subnet 192.168.2.128 network
   192.168.2.129 First IP
   192.168.2.254 Last IP
   192.168.2.255 Broadcast