DNS Flashcards
DNS
DNS REQUEST
DNS
LOAD BALANCER
CDN
CONTENT DELIVERY NETWORK
IP ADDRESS
FORMAT
ISP
INTERNET SERVICE PROVIDER
WHAT IS A WEB SERVER
STATIC CONTENT
DYNAMIC CONTENT
FRONT END
BACK END
VIRTUAL HOST
LAN
VPN
ETHERNET
ROOT DNS SERVER
The root servers act as the DNS backbone of the internet; their job is to redirect you to the correct Top Level Domain Server, depending on your request. If, for example, you requestwww.tryhackme.com, the root server will recognise the Top Level Domain of .com and refer you to the correct TLD server that deals with .com addresses.
RECURSIVE DNS SERVER
A Recursive DNS Server is usually provided by your ISP, but you can also choose your own. This server also has a local cache of recently looked up domain names. If a result is found locally, this is sent back to your computer, and your request ends here (this is common for popular and heavily requested services such as Google, Facebook, Twitter). If the request cannot be found locally, a journey begins to find the correct answer, starting with the internet’s root DNS servers.
AUTHORITATIVE DNS SERVER
An authoritative DNS server is the server that is responsible for storing the DNS records for a particular domain name and where any updates to your domain name DNS records would be made. Depending on the record type, the DNS record is then sent back to the Recursive DNS Server, where a local copy will be cached for future requests and then relayed back to the original client that made the request. DNS records all come with a TTL (Time To Live) value. This value is a number represented in seconds that the response should be saved for locally until you have to look it up again. Caching saves on having to make a DNS request every time you communicate with a server.
COMMON HTML REQUEST HEADERS
HOST
USER-AGENT
CONTENT-LENGTH
ACCEPT-ENCODING
COOKIE
HOST
Host:Some web servers host multiple websites so by providing the host headers you can tell it which one you require, otherwise you’ll just receive the default website for the server.
USER-AGENT
User-Agent:This is your browser software and version number, telling the web server your browser software helps it format the website properly for your browser and also some elements of HTML, JavaScript and CSS are only available in certain browsers.
CONTENT-LENGTH
Content-Length:When sending data to a web server such as in a form, the content length tells the web server how much data to expect in the web request. This way the server can ensure it isn’t missing any data.
ACCEPT-ENCODING
Accept-Encoding:Tells the web server what types of compression methods the browser supports so the data can be made smaller for transmitting over the internet.
COOKIE
Cookie:Data sent to the server to help remember your information (see cookies task for more information).
COMMON HTTP RESPONSE HEADERS
SET-COOKIE
CACHE-CONTROL
CONTENT-TYPE
CONTENT-ENCODING
SET-COOKIE
Set-Cookie:Information to store which gets sent back to the web server on each request (see cookies task for more information).
CACHE-CONTROL
Cache-Control:How long to store the content of the response in the browser’s cache before it requests it again.
CONTENT-TYPE
Content-Type:This tells the client what type of data is being returned, i.e., HTML, CSS, JavaScript, Images, PDF, Video, etc. Using the content-type header the browser then knows how to process the data.
CONTENT-ENCODING
Content-Encoding:What method has been used to compress the data to make it smaller when sending it over the internet.
HTTP STATUS CODES
500-599
SERVER ERRORS
This is reserved for errors happening on the server-side and usually indicate quite a major problem with the server handling the request.
HTTP STATUS CODES
400-499
CLIENT ERRORS
Used to inform the client that there was an error with their request.
HTTP STATUS CODES
300-399
REDIRECTION
These are used to redirect the client’s request to another resource. This can be either to a different webpage or a different website altogether.
HTTP STATUS CODES
200-299
SUCCESS
This range of status codes is used to tell the client their request was successful.
HTTP STATUS CODES
100-199
INFORMATION RESPONSE
These are sent to tell the client the first part of their request has been accepted and they should continue sending the rest of their request. These codes are no longer very common.
COMMON STATUS CODES
201
CREATED
A resource has been created (for example a new user or new blog post).
COMMON STATUS CODES
200
OK
The request was completed successfully.
COMMON STATUS CODES
301
MOVED PERMANENTLY
This redirects the client’s browser to a new webpage or tells search engines that the page has moved somewhere else and to look there instead.
COMMON STATUS CODES
302
FOUND
Similar to the above permanent redirect, but as the name suggests, this is only a temporary change and it may change again in the near future.
COMMON STATUS CODES
400
BAD REQUEST
This tells the browser that something was either wrong or missing in their request. This could sometimes be used if the web server resource that is being requested expected a certain parameter that the client didn’t send.
COMMON STATUS CODES
403
FORBIDDEN
You do not have permission to view this resource whether you are logged in or not.
COMMON STATUS CODES
401
NOT AUTHORIZED
You are not currently allowed to view this resource until you have authorised with the web application, most commonly with a username and password.
COMMON STATUS CODES
404
PAGE NOT FOUND
The page/resource you requested does not exist.
COMMON STATUS CODES
405
METHOD NOT ALLOWED
The resource does not allow this method request, for example, you send a GET request to the resource /create-account when it was expecting a POST request instead.
COMMON STATUS CODES
500
INTERNAL SERVICE ERROR
The server has encountered some kind of error with your request that it doesn’t know how to handle properly.
COMMON STATUS CODES
503
SERVICE UNAVAILABLE
This server cannot handle your request as it’s either overloaded or down for maintenance.
ENCAPSULATION
OCTET
BIT
B
BYTE
TCP
TRANSMISSION CONTROL PROTOCOL
UDP
USER DATAGRAM PROTOCOL
TCP USAGE
TCPis used for situations such as file sharing, internet browsing or sending an email. This usage is because these services require the data to be accurate and complete (no good having half a file!).
UDP USAGE
STREAMING
TCP ADVANTAGES
Guarantees the accuracy of data.
Capable of synchronising two devices to prevent each other from being flooded with data.
Performs a lot more processes for reliability.
TCP DISADVANTAGES
Requires a reliable connection between the two devices. If one small chunk of data is not received, then the entire chunk of data cannot be used.
A slow connection can bottleneck another device as the connection will be reserved on the receiving computer the whole time.
UDP ADVANTAGES
UDPis much faster than TCP.
UDPleaves the application layer (user software) to decide if there is any control over how quickly packets are sent.
UDPdoes not reserve a continuous connection on a device as TCP does.
UDP DISADVANTAGES
UDPdoesn’t care if the data is received.
It is quite flexible to software developers in this sense.
This means that unstable connections result in a terrible experience for the user.
TCP LAYER
TRANSPORT LAYER
UDP LAYER
TRANSPORT LAYER
OSPF
OPEN SHORTEST PATH FIRST
MAC
MEDIA ACCESS CONTROL
NIC
NETWORK INTERFACE CARD
DHCP
DYNAMIC HOST CONFIGURATION PROTOCOL
RESPONSIBLE FOR ASSIGNING AN IP ADDRESS TO THE SYSTEMS THAT TRY TO CONNECT TO A NETWORK
AUTHENTICATION
AUTHORIZATION
BROKEN ACCESS CONTROL
PRINCIPLE OF LEAST PRIVILEGE
OWASP TOP 10
WHAT IS INJECTION
HOW TO AVOID INJECTION
proper validation and sanitization of the user’s input.
TCP PACKET
TCP PACKET HEADER
THREE-WAY- HANDSHAKE
UDP PACKET
UDP PACKET HEADER
STATEFUL FIREWALL
STATELESS FIREWALL
PROXY FIREWALL
NGFW
NEXT GENERATION FIREWALLS
PACKET FILTERING FIREWALLS
VPN TECHNOLOGY
PPP
VPN TECHNOLOGY:
PPTP
ThePoint-to-PointTunnelingProtocol (PPTP) is the technology that allows the data from PPP to travel and leave a network.
PPTP is very easy to set up and is supported by most devices. It is, however, weakly encrypted in comparison to alternatives.
VPN TECHNOLOGY:
IPSEC
Internet Protocol Security (IPsec) encrypts data using the existingInternetProtocol (IP**) framework.
IPSec is difficult to set up in comparison to alternatives; however, if successful, it boasts strong encryption and is also supported on many devices.
VPN BENEFITS
ALLOWS NETWORKS IN DIFFERENT GEOGRAPHICAL LOCATIONS TO BE CONNECTED
OFFERS PRIVACY
OFFERS ANONYMITY
WHAT IS A ROUTER
Routers are network devices responsible for forwarding packets between networks. They make intelligent decisions based on routing protocols and their understanding of network topology to send data to the correct destination.
It’s a router’s job to connect networks and pass data between them. It does this by using routing (hence the name router!).
VPN USES
Uses: VPNs are often used to protect sensitive data and to hide the user’s IP address. They are also commonly used for remote access to a corporate network, for privacy when browsing, and to bypass geographical internet restrictions.
WHAT LAYER IS ROUTING ON?
LAYER 3 OF OSI (NETWORK LAYER)
WHAT IS ROUTING?
Routing is the label given to the process of data travelling across networks. Routing involves creating a path between networks so that this data can be successfully delivered.
IP HEADERS
TIME TO LIVE
CHECKSUM
SOURCE ADDRESS
DESTINATION ADDRESS
TIME TO LIVE
This field sets an expiry timer for the packet to not clog up your network if it never manages to reach a host or escape!
SOURCE ADDRESS
The IP address of the device that the packet is being sentfromso that data knows where toreturn to.
CHECKSUM
This field provides integrity checking for protocols such as TCP/IP. If any data is changed, this value will be different from what was expected and therefore corrupt.
DESTINATION ADDRESS
The device’s IP address the packet is being sent to so that data knows where to travel next.
PACKET VS FRAME