Comptia A+ IP and TCP/UDP

TCP/IP

"Transmission Control Protocol / Internet Protocol It is a set of communication protocols that allows computers, smartphones, servers, and other devices to communicate over a network, including the internet."

Default Gateway

"the IP address of a router on a local network that acts as an access point to other networks or the internet

• the device (usually your router) that allows your computer to communicate with devices on other networks, including the internet"

IPv4 address

"- dotted decimal

• four decimal numbers separated by periods, with values from 0 to 255

• eg. 104.244.42.129"

How large is an IPv4 address?

"32 bits 8 bits x 4"

Subnet mask

"a number that tells your computer which devices are on its local network and which devices are on a different network

• dives an ip address into a network portion and a host (device) portion"

What does a TCP/IP IPv4 subnet mask of 255.255.255.0 mean if the ip address is 192.168.4.33?

The network ID is 192.168.4 and the host address is 33

What is a common subnet mask?

255.255.255.0

2 hosts are always subtracted from total useable hosts on a subnet mask for what?

network and broadcast

What numbers can be in an IPv4 addresss?

0 -255

NAT

"Network address translation

• a function on a router that lets devices using private IP addresses communicate with the internet through a public IP address."

Public vs private IP address

"A private IP address is used inside a local network, such as your home Wi‑Fi. Your router assigns addresses like 192.168.1.25 to your devices

• not internet routable but can be routed internally

A public IP address is used to identify your network on the internet. Your internet provider usually assigns it to your router."

What oranisation sets the standard used for IPv4 addressing?

"RFC 18 (request for comment)"

What are RFC 18 private IP address ranges? And how to easily memorise them?

"10.0.0.0 - 10.255.255.255 172.16.0.0 - 172.31.255.255 192.168.0.0 - 192.168.255.255

• any address starting 10
• any address starting 172.16 through 172.31, inclusive
• any address starting 192.168"

IPv6 address length

128 bit

IPv6 how to write

"Hexadecimal

• eight groups of hexadecimal digits, separated by colons
• each hextet contains one to four digits

eg. 2001:0db8:0000:0000:0000:ff00:0042:8329

You can shorten it in two ways:

1. Drop leading zeros in any group: 0db8 becomes db8; 0042 becomes 42.
2. Replace one consecutive run of all-zero groups with ::, once per address. So the example becomes:

eg. 2001:db8::ff00:42:8329"

Subnetting with IPv6?

"Less need - there are more than enough addresses

• usually first 64 bits is the network prefix (/64), and last 64 bits is the host network address"

On a 255.255.255.0 subnet mask, which is the network portion and which is the host portion?

"255.255.255 is the network portion 0 is the host portion"

What are CIDR /8, /16 and /24 subnet masks?

"255.0.0.0 : /8 255.255.0.0 : /16 255.255.255.0 : /24"

What are CIDR /8, /16 and /24 subnet masks equivalent in binary notation?

"11111111.00000000.00000000.00000000 : /8 11111111.11111111.00000000.00000000 : /16 11111111.11111111.11111111.00000000 : /24"

Multiplexing

"combines multiple data streams so they can share one communication channel. At the receiving end, the streams are separated again.

For example, a computer can use different port numbers to keep several network conversations straight over the same connection. This lets those conversations share the network link."

TCP - transmission control protocol

"connection oriented

• a formal connection setup and close reliable delivery
• recovery from errors
• can manage out of order messages or retransmissions flow control
• the receiver can manage how much data is sent"

UDP - user datagram protocol

"connectinless

• no formal open or close to the connection unreliable delivery
• no error recovery
• no reordering of data or retransmissions no flow control
• sender determines the amount of data transmitted"

DHCP

"Dynamic host configuration protocol

• automatic IP addressing
• automatically gives a device its network settings, such as an IP address, subnet mask, and default gateway. Think: join Wi‑Fi, get settings automatically
• uses UDP (connectionless protocol)"

TFTP - Trivial file transfer protocol

"- transfers files in a simple way, often for tasks such as loading a device’s configuration or boot files over a network

• uses UDP (connectionless protocol)"

What happens when data doesn't get through when an application using UDP?

"- the application itself might keep track and decide whether or not data needs to be retransmitted

• it might not do anything if data is lost"

HTTPS

"encrypts the connection between your browser and the website, helping protect information in transit, such as passwords or payment details. You’ll usually see it shown as a padlock in the browser address bar

• uses TCP"

SSH - secure shell

"lets you securely connect to and manage another computer over a network, often using a text-based command line

• uses TCP"

Non ephemeral ports

"the fixed, well-known ports that network services use to listen for connections

• ports 0 through 1023
• usually on a server or service"

Ephemeral port number

"a temporary port number your computer picks for one side of a network connection

• also known as a client port number
• ports 1024 through 65535
• determined in real time by the client"

What number can a TCP or UDP port be?

"any number between 0 and 65535

• however TCP 80 is not the same us UDP 80 "

Are port numbers secret?

"No

• port numbers are for communication, not security
• service port numbers need to be well known"

APIPA

"If a DHCP server is not available and a static/ manual IP address has not been configured

• the machine creates its own IP address based on APIPA (Automatic Private IP Addressing)
• can only be used communicate on the device's local network"

Link Local address

Another word for an APIPA address

APIPA Address ranges

169.254.1.0 to 169.254.254.255 (169.254.x.x)

Static Address

"Assign all IP parameters manually

• you need to know very specific details"

DNS server assignment

"- usually assigned automatically from DHCP server

• can also be configured manually"

Loopback address

lets a device send network traffic to itself. It’s useful for checking whether that device’s own networking software is working, without sending traffic to another computer

IPv4 loopback address

127.0.0.1 (often written as 127.x.x.x)

IPv6 loopback address

::1

DHCP server

"- usually integrated into router

• in a business setting multiple DHCP servers should be installed for redundancy"