---
# System prepended metadata

title: Network Fundamentals
tags: [Fundamentals]

---

# Network Fundamentals

Moving data from one device to another.

#### OSI - Open Systems Interconnect

- *Application Layer*		: HTTP/HTTPS
- *Presentation*			: (Antiquated)
- *Session Layer*			: (Antiquated)
- *Transport Layer*			: TCP
- *Network Layer*			: Addressing Scheme(IP Addressing, IP Routing)
- *Data Link Layer* 		: Ethernet (Device to router, router to cable modem. ) Ethernet allows high speed communication, 
- *Physical Layer* 		    : Twisted Pair, CoAx, Fiber Optics, Wirless 
- 					DOCSIS-3 = **Data Over Cable Service Interface** Specification
					Ethernet is a family of wired computer networking technologies commonly used in local area networks, metropolitan area networks and wide area networks. It was commercially introduced in 1980 and first standardized in 1983 as IEEE 802.3

**Protocol Categories**
- Data Transfer Protocol 
- Authentication Protocols
- Network Service Protocols
- Network Management Protocols
- Audio/Visual Protocols



**Hyper Text Document Transfer**

```
Layer 7		HTTP	HTTPs
Layer 4		80	    443
```

**File Transfer**

*SMB*: Server Message Block. (Network file share)
```
Protocol	|FTP	|	sFTP 	|	TFTP	|	SMB	|
Port		|20/21	|	22	|	69	|	445	|
```

**Email**
POP3 - Post Office Protocol v3
IMAP - Internet Message Access Protocol
SMTP - Sends message from client to email server. Server sends to receipient.		
```
Protocol	|POP3			|IMAP			|SMTP	|
Port		|110/995		|143/993		|587/25/465		|

```

**Authentication**

LDAP - Lightweight Directory Access Protocol

LDAP 		LDAPs
389			636

**Network Services**

**DHCP** Dynamic Host Configuration Protocol
When we plug-in to the network DHCP automatically hands out IP address to it. It is typically the wireless access point for your home network. 

Port 67/78
//Flow below
Work Station --> Message --> DHCP SErver
DHCP Server --> IP Address, Sunebet , Default Gateway, DNS Server

**DNS**
is to lookup hostname into an ip address.
uses port 53 
nslookup command.
* * *


**NTP :Network Time Protocol**

UTC : Coordinated Universal TimeNT
Controlled by Governments.

Imaginary Line from NP to South pole . Greenwhich (East London). Prime Meridian.

Time at Midngight is considered as 0 hour.

Midnight in Greenwhich is 5:30 in the morning New Delhi.
UTC


Greenwich Mean Time  - GMT is a Time zone
UTC is a time Standard. This means that no country or territory officially uses UTC as a local time.

**Network Management Protocols**

Telnet  - Clear Text. Operates on Port 23
SSH  - Secured Shell (Encrypted)  . Port 22

SNMP - Simple Network Management Protocols.

SNMP Server --> Walk the tree and get all the information about clients in the network. Network admin can look in to the SNMP Server can look in to the SNMP server. 

SNMP Trap --> If something breaks client can send can send SNMP Trap to SNMP server. 

RDP --> Remote Desktop Protocol.  port 3389

**Audio Visual**
H.323  1720/`1721` --> Used for Video conferencing.
H
For Voice call using VOIP  , SIP protocol is used. 
SIP stands for Session Initiation Protocol. SIP Uses 5060/5061 Ports. Used to setup a voice call. 



***

Transport Layer (Layer 4)  TCP 
TCP - Transmission Control Protocol

**3 way handshake**

Client --> SYN --> Server
Server --> SYN-ACK --> Client
Client --> ACK --> Server

**4 Way Disconnect (Graceful DIsconnect)**

Server --> FIN --> Client
Client --> FIN-ACK --> Server 
Client --> FIN --> Server 
Server --> FIN-ACK -->Client

TCP Reset   // hanging up abrutptly
RST

**UDP** User Datagrapm Protocol

No session, no three way handshake
Used for efficient data transfer. 


**Transport Layer Addressing** 
Port #

Source Port# and Destination Port#
Port# are catgorized in to two


Server / Wellknown / Registered port
Client / Ephemeral Port numbers.


* * *

IP Addressing
***


IP Addressing is at layer 3


IP Address borken in to 4 portions. Each portion range 0-255

Network portion + host portion

Each one of these 4 numbers are decimal representation of binary numbers.
An IP address is a 32 bit value broken in to 4 octects. 


**Classful Addressing (Before 1995)**

Class A , B, C --> Unicast addersses. 

Class D --> Multicast address. One to many devices. NOt suported on internet. 



	
**Classless Addressing (1995 to present)**
First 3 octects are Netwrok portion and last octect portion is host portion
all binary 1 for network octects and all binary 0s for host portion => Subenet mask. 

The netwrok designer can choose how many bits (out of 32 bits) they want to assign for the network portion and how many bits for the host portion.


IP Address 192.168.  4. 57
Subnet Mask 255.255.255.  0
This means, the first three octects represents network portion.  


First Address of the subnet is netowrok address 192.168.4.0 
Last Address of the subnet is BroadCast address 192.168.4.255
So out of 256 the above two are gone and you are left with 254 hosts.



**Address Types**
An IP netwrok has three types of Addresses.
Network Address, Broadcast address and Host Address.

**Network Address** // Compare to Zip Code
	- Identifier for a group of devices.
	- Network Prefix
	
if we have a subnet mask and a device ip address we can find out the network addresss. The network address will have all binary zeroes in the HOST portion of the address. 


*Question:* If you have a network mask of 255.255.255.128 , what will be your etwork address/broadcastaddess/how many hosts

Ans: Network Address will be 192.168.4.0
Broadcast address will be 192.168.4.127 
you can have only 126 hosts .



**Broadcast Address** // Address that can send a message to all devices at once.
	- Identifier for all devices on a network. 
	- In the HOST portion all binary 1's.  (Refer back to the question above)
**Host Address** // Unique device 
	- identifies unique device on a network.
	- Anything that is not a network address & not a broadcast address.

	Host address is in between Network address and broadcast address.
	
**CIDR Notation**
Classless Inter Domain Routing
Look at the subnet mask below and equivalent binary.
```

     255      255      255        0 
11111111 11111111 11111111 00000000
```
First 3 octets is the network prefix and it is 24 bits.  The number of bits in the network portion will be represented by /24. 

Example: 203.0.113.10/24 


**Private Addresses**

Internal Private Use only. Determined by IETF (Internet Engineering Task Force) is the authority. 

IPv4 addresses are allocated by IANA(Internet Assigned Numbers Authority)
RFC 1918
```
      10.       0.		 0.		  0 to       10.     255     .255     .255   
00001010.00000000.00000000.00000000 to 00001010.11111111.11111111.11111111

// above is in a /8 subnet. 

	 172.      16.       0.       0	to      162.      31.     255.     255
10101100.10100010.00000000.00000000 to 10100010.00011111.11111111.11111111
// above is a /12 subnet


     192.     168.       0.       0 to      192.     168.     255.     255
11000000.10101000.00000000.00000000 to 11000000.10101000.11111111.11111111

//above is in a /16 subnet


```

**APIPA** - Automatic Private IP Addressing. 169.254.0.0/16 . Windows uses APIPA addresses to help non technical users. If a device has this address this means there is a problem in the network. 

**Loopback Address** 127.0.0.1 to check if your IP stack on your OS works correctly.

```
A loopback address is a special IP address, 127.0.0.1, reserved by InterNIC (The Network Information Center) for use in testing network cards. This IP address corresponds to the software loopback interface of the network card, which does not have hardware associated with it, and does not require a physical connection to a network. The loopback address allows for a reliable method of testing the functionality of an Ethernet card and its drivers and software without a physical network. It also allows information technology professionals to test IP software without worrying about broken or corrupted drivers or hardware.


```

**PING** - Packet InterNet Groper. Sends a packets to an ip address send back a response if IP is working. 

Inordedr for two devices to communicate each device should be on the same IP network. If they are on different network we need to use router. 


**Components of a IP Network** 
Network IP Address: All binary 0's in host portion.
Broadcast IP Address: All binary 1's in host portion
Host IP Address


Network 10.0.0.0/8 
Range 	10.0.0.0  - 10.255.255.255

Subnet from the above subnet

	Network 10.0.10.0/24 
	Range 	10.0.10.0  - 10.0.10.255

VLSM - Variable Length Subnet Masking


**IP v6**

Bit
	- 1 OR 0
Nibble - 4 bits
	- 1010
	- Hex - 0xA
Byte - 8 Bits 
	- 11111111
	- Hex
Hextet - 16 bits

IP v6 Address listed as hextets
128 bits long = 32 nibbles = 8 hextets.

First 64 bit Network Portion
Latter 64 bit is interface identifier

SLAAC -- Stateless Adress Auto Configuration

**ETHERNET & Switching**

CSMA/CD
	Carrier Sense Multiple Access with Collision Detetction
	
Collission Domains

Duplex & Speed
	Half Duplex. Eg: Walkie / Talkie
	Full Duplex: Eg: Telephone
Ethernet Frame
Switch Operation


**Network Topologies**

- Bus
	- Antiquated. (Single wire)
- Ring 
	- Antiquated (Token Ring)
- Star
	- Modern
- Layer2 Switch 
	- Keep track of mac address in mac address table.
	- Frame header.


**Switching Features**

Broadcast Domain : *Receive a message with all Fs in the mac address. 
Broadcast messages will be send out to all active interfaces. If there are two switches this can lead to Broadcast Storm: Multiple switches causing too much broadcast traffic.Solved by Spanning Tree Protocol. Shutdown redundancy*

Home switches does not have spanning tree implemented. Only enterprise has this. 

**VLAN**  
Each broadcast domain a VLAN

Up to 4000 VLANs on a single switch.

Trunk Link --> designed to connect switches 


**IP Routing**

IP Routing happens at Network Layer (Layer 3)
Respnoseible for End to end communication. 

Routers will have at least two interfaces.

IP Packet 
Internet Control Message Protocol
```
Destination MAC		Source MAC	Layer3 Protocol		Source IP		Destination	 IP		TTL		Other		ICMP

```
TTL is used to prevent loops in Layer 3

Destination MAC address is obtained with the help of **Address Resolution Protocol** (ARP). 
Devices maintain ARP Cache (Table. 90 seconds)

NOTE: MAC Address table is purely on Layer 2. Exists only on switch.

Default Gateway : Gateway is another term for Router. 



Dynamic Routing
	- RIP - Antiquated (Actually RIP)
	- EIGRP - Enhanced Interior Gateway Routing Protocol
	- OSPF - Open Shortest Path First
	- BGP - Border Gateway Protocol
	


**Layer 1 topologies**
	
LAN - Local Area Network
WLAN - Wireless LAN

WAN - WIde Area Network
	- CAN Campus Area Network (Silicon Valley as example)
	- MAN Metropolitan Area Network ()
	
SAN - Storage Area Network 
PAN - Personal Area Network (Bluetooth)


**NAT**
Network Address Translation

:abc: Protocol-Port Mapping
```
Category	Protocol	Port	Descritpion
Data Transfer	HTTP	80	Hyper Text Transfer Protocol
	HTTPs	443	Hyper Text Transfer Protocol (Secured)
	FTP	20/21	File Tansfer Protocol
	sFTP	22	Secured File Tansfer Protocol
	TFTP	69	Trivial File Transfer Protocol.
	SMB	445	Server Message Block. (Used in Mapped Network Drive)
	POP 3	110/995	Post Office Protocol v3. (Email incoming)
	IMAP	143/993	Internet Message Access Protocol (Email Incoming)
	SMTP	25/465/587	Simple Mail Transfer Protocol (Email Outgoing)
Authentication	LDAP	389	Lightweight Directory Access Protocol
	LDAPs	636	
Network Service	DHCP	67/68	Dynamic Host Configuration Protocol
	DNS	53	Lookup hostname into an ip address.
	NTP	123	Network Time Protocol
Network Management	Telnet	23	Shell (clear text)
	SSH	22	Secured Shell (Encrypted)
	SNMP	161/162	Simple Network Management Protocol
	RDP	338	Remote Desktop Protocol
Audio Visual	H.323	1720/1721	Video Conference
	SIP	5060/5061	Voice Call (VOIP)
```