Network Basics
Created Jan 1, 2020 - Last updated: Feb 4, 2024
Network Basics
OSI Model
Application → Deals with applications, people still can read this ( http, ftp )
Prestation (translation ) → Here the data is being converted into a form that can be sent over network ( compression, deCompression , encryption, decryption )
Session → Controls dialog during communication ( establish, manage, and terminate ) communications
Transport → Transfer data between end users responsible of resending any packets that do not receive an acknowledgment ( can guaranteed that data is received )
Network → Routing the data packet based on the IP
DataLink → Send Data to thee physical layer ( data packets are encoded or decoded into bits and got two parts MAC Media access Control and LLC Logical Link Control )
Physical → Define the topology of a network
IP
Consist of Two Parts
1 - Network address
2 - Host address
IPv4
32 bits means 4 octets of 8 bits
1 octet → 8 bits
IPv6
128-bit hexadécimal adress
to convert you to go 4 bits by 4 bits
SubNetMask
get how many bits in the network are used for the network by masking the network part of the ip
A → 255.0.0.0 ( 1 - 128 ) → / 8
B → 255.255.0.0 ( 128 - 191 ) → / 16
C → 255.255.255.0 ( 192 - 223 ) → /24
Usefull formulas
To find the number of possible network ids use
2^numbeOfNetworkBits - 2
To find the number of possible host ids use
2^numberOfHostsBits - 2
UseFull Video
How to calculate the total number of the usable host IDs?
SubNet
Useful Links :
https://www.youtube.com/watch?v=S_EfcLo2Wv0
Dynamic IP Adress
they come from DHCP SERVER ( Dynamic Host Configuration Protocol )
if the pc can’t reach thee server or the server goes down it will assign it self an address
Static IP
Manual IP assigning
DHCP gives ip addresses as lease mean that they will change
if the dhcp server and the machine are not in the same subnet ( means they have different ip settings ) the dhcp server will not get the request cause broadcast doesn’t go outside of their subnets.
that why we use a dhcp relay enable option that way the request will be forwarded to the the dhcp server
TCP/UPD
tcp → transmission control protocol
udp → user datagram protocol
is connectionless mean that there is no 3 way handshake and it just spam data as fast as possible
FTP
ftp → File transport protocol
download and upload files between users
its a connection oriented protocol that uses TCP for file transfer
TFTP
tftp → trivial file transport protocol
used to transfer file inside the network and not the internet
and use udp
SFTP
sftp → secure file transfer protocol
its like ftp and it uses another layer of security means data is encrypted during data transfer using secure shell
SMTP
smtp → simple mail transfer protocol
sends mails and uses tcp protocol
Pop3
is used to receive emails you an only use it download mails on your computer but it doesn’t sync your data and when you do that the email is removed from your mail server unless you say you want to keep a copy
IMA4P
ima4p → internet message access protocol ver 4
it gives you power over your mail server mean you will be able to read and manage your mails and it will also create a copy of your mail automatically and it will also syncs email and folders between the mail server and your computer
HTTP
http → hypertext transfer protocol
used in webserver to load webpages
https
is a secure version of http it will just encrypt the data
Telnet
used to access devices but its not secure that way it used only in local network devices
SSH
ssh → secure shell
cause it encrypt data while sending it create like shell around the connection to to protect the data
ARP
arp → address resolution protocol
used to resolve ip address to mac address
that what is used by computers to communicate with each other
by checking the cache arp the computer will go look for the matching ip address if not found it will send a request looking for the one with that same address if its found the computer will inform the sender of it presence
RARP
reverse ARP convert mac to IP
SCP
scp → secure copy protocol
uses secure shell protocol to safeguard data as it being transferred over a network
SNMP
snmp → simple network management protocol
used to collect data from network devices
Ports
got two protocols TCP/UDP
logical connection that is used by programs to exchange informations
port are identified by unique numbers
0 → 65535
DNS
dns → domain name system
resolve domain name to ip adresses
there is also WINS but it resolves computer names to ip address
NAT
nat → network address translation
translate a set of ip addresses to another set of ip addresses
for example form private to public or from public to private
PAT
pat → port address translation
like nat but it also use the port number
SNAT
static nat
it give computers a permanent public ip addresses
this used for example for mail servers
Proxy
used for cashing data from the internet one use example of this is when a company use this techno to store webpages visited by employees so that the next time an employee visit that page again it load that cached page a proxy can be used also for other things
Benefits
Speed
Bandwidth :
The maximum amount of data transmitted over an internet connection in a given amount of time.
Security
RDP
rdp → remote desktop protocol
CSMA/CD
csma/cd = Carrier Sense Multiple Access with Collision Detection
allow computer to sense if the wire is free before sending if not it waits
mostly used on wireless networks
it will first send aa small packet of data to check if everything is free before sending
Loopback interface
Routing table
contains information about what path the data takes to reach it destination
Routing protocols
collect information about the network and map the best path to transfer data
there is 3 types
Distance vector : factor distance based on how many hops
when of the those protocols is called rip ( routing information protocol ) routers that use it broadcast their information every 30 sec
but ripv2 is better cause it solve the problem of broadcast problem
there is also bgp ( border gateaway protocol ) and its the standard routing protocol of the internet
it determines path direction based on paths and policies
LinkState :
routing protocol that is used by routers to share information and independently map out the best path on the network .
OSPF → open shortest path first
a routing protocol that is used to determine the correct rout for data packet to take for their destination
it collect information from other routers using IP and create a topology map of the network
IS-IS → intermediate system to intermediate system
Routers are organized into a domain means groups and IS-IS functions inside those domains but this service use clns ( connectionless network service ) to communicate with other routers
Hybrid :
EIGRP → Enhanced interior gate-away routing protocol and as the name say it
it’s combination of Distance vector and LinkState and only runs on cisco routers
fast, less overhead can support many network layer protocols
SIP
sip → session initiation protocol
Establishes communication session over the internet.
example :
VoiP ( voice over IP)
term that used for voice communication over ip networks
also used for instant messaging and conferencing services
RTP
rtp → real time transport protocol
the internet standard for transporting real-time data such as streaming audio and video
it used over udp so it doesn’t guarnte data delivery
used also with RTCP → real time transport protocol and that enable you to monitor the quality of the data being delivered
uses both unicast and multicast
ISDN
isdn → integrated service digital network
International standard foor digital transmission over odinary telephone lines
T1 ( europe is E1)
t1 → T carrier level one
commonly used internet service for business today
carries data or voice
T3
t3 → T carrier level three
mainly used by ISP ( internet service providers ) and they are connected directly to the internet
OCx
OCx → optical carrier
Describes the speed of networks that can be carried on SONET ( Synchronous Optical Network )
DSL
dsl → digital subscribier line
it can carriers voice and data at the same time
ADSL
adsl → asymmetric digital subscribier line
download speed > upload speed
SDSL
sdsl → symmetric digital subscribier line
download speed == upload speed
VDSL
vdsl → very high bit dsl
Remote access services
RAS
ras → remote access service
service that enable you to connect to a computer from a remote location
SLIP
slip → serial line internet protocol
Designed so data can transmit over serial ports and modem connections
Doesn’t support encryption or authentication
all information are sent in clear text
does not provide and error checking limited to using only tcp/ip
PPP
ppp → point-to-point protocol
the standard remote access used today
support encryption or authentication
is secure
PPPoE
pppoe → point-to-point protocol over ethernet
uses PPP over ethernet
used to encapsulate PPP frames in ehternet frames
Developed for DSL, cable modem, or wireless connection to the internet
used also to connect multiple users on LAN to a remote site sharing a common device
PPTP
pptp → point to point tunnelling protocol
used for creating vpns
ensure that data transfer is secure by creating a secure tunnel
GRE
gre → generic route encapsulation
used with pptp in creation of a VPN network
create the tunnel in PPTP
Encapsulates the data in secure manner
VPN
vpn → virtual private network
a private communication network that uses public network to establish a remote connection
encrypt data when sending decrypt data when receiving
provide a link btw two points over the internet
vpn concentrator a device that create the vpn connection and manages the delivery of the messages btw the vpn computer devices
authentiate users encrypt the data and assign tunnel/ip adresses to users
not always needed only in cases of managing a lot of vpn connections
VPN TYPES
- SITE TO SITE → connection between two organisations
- HOST TO SITE → connection between simple computer and organisations
- HOST TO HOST → connection between two computers
Authentication
PAP
pap → password authentication protocol
not safe everything is sent in clear text
CHAP
chap → challenge hand shake protocol
Encrypt username and password
uses 3 way handshake
the server send a challenge to the client the client will use the hash it got and send a response back then the server will check using his hash and if the value matchs its all good
MS-CHAP
ms-chap is also CHAP but by microsoft
ms-chap 2 both client and server are authenticated means they challenge each other
Radius
radius → remote authentication dial-in service
enable a single server such as domain controller to handle all authentications
enable an organisation to store all user related to data to one place
a radius server makes the request on the user’s behalf after authentication
Kerberos
Developed by mit and it give users tickets that makes them able to access devices on the network
EAP
eap → extensible authentication protocol
is an extension to PPP support many methods of authentication
commonly associated with smart cards
Security protocol
IPSec
Ipsec → internet protocol security
Encrypt data
there is key that locks and unlocks the data while it travel through a network
it got two modes :
- Transport mode → message portion is encrypted
- Tunnel Mode → entire packet is encrypted
L2TP
l2tp → layer 2 tunneling protocol
Combination of Cisco’s layer 2 forwarding and PPTP
it authenticate both the computer and the user using a digital certificate to insure that the data wasn’t change during the process
to prevent man in middle attacks
SSL
ssl → secure socket layer
It’s a protocol that provide security on the internet
Provides security in 3 ways :
- Authenticate the server
- Authenticate the client
- Encrypt the data
TLS
tls → the latest industry standard SSL protocol it authenticate the server and the client and encrypt the data
Made up of 2 layers :
- TLS Record Protocol → Makes the connection is private and reliable
- TLS Handshake Protocol → Server and client can negotiate encryption algorithm and cryptography keys before the data is sent
802.1x
Used for both wired and wireless networks
Control network access by word
Port based authentication