Part 1 - Internet and HTTP

Question 1

What is a web application?

Answer 1

graphical computer program that a user interacts with in a web browser. They often also have a server-side component that runs on a web server.
Also needs the use of hypertext.

Question 2

Why do we use the web?

Answer 2

We use the web to request, search, navigate and share info. Also to access and operate software.

Question 3

Give me some example use case of the web to request, search, navigate and share info.

Answer 3

A social media website, we can “search” for users on the social media website, “request” to follow them, and share our own posts on the website.

Question 4

Give me an example use case of accessing and operating software

Answer 4

VScode is a website! it is a software used to create programs, etc. An IDE-integrated development environment

Question 5

What is Ethernet?

Answer 5

a fundamental networking protocol that frames data for transmission over physical media (cables).

Ethernet works within a network, i.e. a laptop uses ethernet to talk to a Wi-Fi router

Question 6

In the context of web-applications and architectures, how does ethernet work? Give an example

Answer 6

Ethernet frames carry the network-level data that is under higher-level protocols like HTTP and web requests.

When you send an HTTP request in your app, it travels through multiple layers of protocols. At the lowest level, it’s carried inside an Ethernet frame, which is like a delivery box that helps it reach its destination.

Question 7

What is an ethernet frame?

Answer 7

Structured packets of data transmitted over ethernet.

Question 8

What are the key components of an Ethernet Frame?

Answer 8

Preamble - syncs sender and receiver by providing a signal to start processing the frame
Start Frame Delimiter - start of ethernet frame
Destination MAC address - unique address of recipient hardware device
Source MAC address - unique address of sender hardware device
Type/Length Field - Specifies protocol (IPv4, ARP) or payload size
Payload - data being transmitted
Frame Check Sequence (FCS) - ensures integrity by detecting errors in transmission

Question 9

Ethernet frames are important to the web. Why is knowing the minimum packet size that can be sent over an ethernet frame important?

Answer 9

Since ethernet frames have a minimum packet size, smaller data must be padded to meet the size requirement.

Knowing this, ensures efficient data transmission without unnecessary overhead. As you can send more data to rid of the unnecessary overhead.

Question 10

Ethernet frames are important to the web. What do we know about the potential waste in a transmission?

Answer 10

Transmitting small amounts of data (1 byte) incurs overhead from headers and trailers.

Headers can be disproportionately large compared to the actual payload.

Question 11

What is fragmentation in ethernet frames?

Answer 11

If a message exceeds the maximum transmission unit (MTU) it must be fragmented (split) into multiple frames.

Question 12

What does fragmentation do to latency?
Why does this happen?

Answer 12

Splitting large messages across frames adds latency because you need to reconstruct them at the destination.

Ensuring payloads fit within a single frame minimizes these delays.

Question 13

Why is ethernet crucial to understand when optimizing web applications? What can we do to keep things optimal?

Answer 13

Ethernet is prevalent, so understanding its limitations (message exceeding MTU–> causing latency) is crucial.

Keeping data smaller than 1.5 KB ensures staying within a single frame, avoiding fragmentation and in turn reducing latency

Question 14

If we just need to keep data small, why not just send lots of small data?

Answer 14

Sending minimal data (e.g., a 1-byte payload) still incurs the full size of Ethernet headers (14 bytes), frame check sequence (4 bytes), and potentially IP/TCP overhead.

Question 15

What are the problems with ethernet frames in terms of communication? (Hint: Is ethernet routable?)

Answer 15

Ethernet is not routable.

Ethernet frames are limited to communication with a local network.

To communicate across networks (between a computer and a server on the internet), we need a routable protocol like IP.

Question 16

How did we fix the problem of ethernet not being able to communicate between different networks?

Answer 16

Introducing IP (IPv4),

uniquely identifies devices on a network, enabling efficient communication across billions of devices.

Question 17

What is IPv4?

Answer 17

Core Protocol that allows devices on different networks to communicate globally.
Assigns addresses to devices, within a network

Question 18

What kind of addresses does IPv4 give?

Answer 18

32-bit addresses: represented as 4 decimal octets

e.g 192.168.0.1

Around 4.3 billion unique addresses

Question 19

Is IP stateless?

Answer 19

Yes, IP does not maintain any connection state, simply routes packets independantly.

Question 20

What was the problem with IPv4?

Answer 20

We ran out of addresses. Due to the rapid growth of devices, (IoT), IPv4 ran out of available addresses, leading to the adoption of IPv6 as a successor, providing a vastly larger address space.

Question 21

How is IPv6 is an improvement form IPv4?

Answer 21

IPv6 expands the address space of Ipv4, allowing for virtually infinite addresses, solving the IPv4 exhaustion issue

Increased address size from 32 to 128 bits

Question 22

What kind of protocols does IPv6 and IPv4 support?

Answer 22

They both support TCP/UDP ensuring compatibility with existing transport protocols used in web apps

Question 23

How are IPv6 addresses different from IPv4?

Answer 23

Written in hexadecimal separated by colons.

ex. 2001:0db8:0000:0000:0000:0000:0000:0001

Question 24

How can the long addresses of IPv6 be abbreviated?

Answer 24

omitting leading zeros and consecutive blocks of zeros

e.g.

2001:0db8:0000:0000:0000:0000:0000:0001
goes to
2001:db8:0:0:0:0:0:1
which can go to:
2001:db8::1

Question 25

How are the host and port representations different in IPv4 and IPv6?

Answer 25

IPv4: 192.168.1.1:443 (host:port) IPv6: https://[2001:db8::1]:443/ [host]:port Colons are part of the address in IPv6, so you have to over the host in square brackets to separate it from the port

Question 26

What is UDP?

Answer 26

User Datagram Protocol, a lightweight. transport protocol. Is connectionless, meaning no session between sender and receiver. Is designed for applications that can handle communication independently with out requiring guarantees from the transport layer

Question 27

What are checksums?

Answer 27

UDP includes a checksum field for basic error checking and data integrity. It does not guarantee reliability but can detect some corruption.

Question 28

What do the port numbers UDP provides do?

Answer 28

It provides port numbers for application level multiplexing, enabling multiple applications to use the same network connection.

Question 29

Is UDP stateless?

Answer 29

Yes, unlike TCP, UDP does not maintain a connection state between the sender and the receiver.

Question 30

What does it mean when it is said that "UDP is lossy and unordered"

Answer 30

Data packets (datagrams) sent over UDP can be - Lost (never received by destination) - Received out of order (Sent: 0,1,2,3; Received: 0,2,1,3) UDP does not retransmit lost packets or reorder them

Question 31

What does UDP guarantee?

Answer 31

Nothing; UDP does not guarantee - delivery of packets - order of packets - protection against duplication

Question 32

Why is UDP used in real-time applications?

Answer 32

Prioritizes low latency over reliability, making it suitable for video streaming and gaming

Question 33

What are the key characteristics of UDP?

Answer 33

Stateless, lossy, connectionless, unordered, no guarantees.

Question 34

What is DNS?

Answer 34

Domain Name Service System that maps human-readable domain names (google.com) to IP addresses (172.217.164.110)

Question 35

What can DNS bind to?

Answer 35

Can bind: a name to an IP address. (e.x. google address) a name to another name or a set of IP addresses. (ai.com => chatgpt.com)

Question 36

What are DNS records?

Answer 36

A records: Map a domain name to an IP address. CNAME Records: Point one domain name to another (ai=>chatgpt)

Question 37

How does DNS work with IPv4 and IPv6?

Answer 37

Seamlessly, (IPv6)AAAA records (IPv4) A records

Question 38

what are tools we can use to check DNS?

Answer 38

host: simple tool for DNS lookups dig: Detailed DNS query tool nslookup: Legacy tool for DNS troubleshooting

Question 39

What is TCP?

Answer 39

A transport protocol used for reliable communications between devices over the internet. Ensures data is delivered in order, without loss, and without duplication.

Question 40

Is TCP connection oriented?

Answer 40

Yes, TCP is connection oriented, meaning it establishes a connection before data transfer begins

Question 41

How does TCP establish a connection?

Answer 41

Establishes a connection by using a 3-way handshake: SYN: Client requests a connection SYN-ACK: Server acknowledges the request and sends its own request to connect. ACK: Client acknowledges the server's request, completing the handshake

Question 42

Does TCP maintain order?

Answer 42

Yes, data is reassembled in the correct order at the receiving end. 0, 1, 2, 3, 4 -> 0, 1, 2, 3, 4

Question 43

Is TCP prevalent?

Answer 43

Yes, TCP is widely used and is the backbone of most internet applications including: HTTP (web browsing) FTP (File browsing) SMTP (email) IMAP/POP3 (email retrieval)

Question 44

What do firewalls do?

Answer 44

Usually prevent hosts from communicating on certain ports, or hosting services.

Question 45

What is the impact of firewalls on HTTP and Web Clients

Answer 45

Firewalls often block inbound traffic unless explicitly allowed. For HTTP and web clients: Web clients (like browsers) are generally not allowed to act as web servers. Communication must be initiated by clients (e.g., browsers making HTTP requests) rather than the web server pushing data.

Question 46

What is HTTP?

Answer 46

Hypertext Transfer Protocol

Question 47

What is Hypertext?

Answer 47

refers to the text that contains links to other texts or resources HTTP facilitates the transmission of hypertext across the web, allowing users to navigate between resources (e.g. web pages)

Question 48

How does HTTP transport?

Answer 48

HTTP serves as the application-layer protocol to transport requests and responses between clients (browsers) and servers. Relies on lower layer protocols (TCP/UDP) for actual data transfer

Question 49

What does Protocol mean in terms of HTTP?

Answer 49

A set of rules that define how communication occurs between systems

Question 50

Is HTTP stateless?

Answer 50

Yes! each request-response cycle is independant of one another

Question 51

What kind of headers does HTTP allow the use of?

Answer 51

Custom Headers, allowing for extendable functionality. e.g. Developers can define headers for specific use cases (X-Custom-Header) or adopt new features without modifying the protocol itself

Question 52

What kind of request/command pattern does HTTP use?

Answer 52

HTTP uses a request/command oriented pattern, where the client sends requests (GET/POST etc) and servers respond with appropriate actions and data

Question 53

What kind of pairing does HTTP rely on?

Answer 53

HTTP relies on the Client-Server Model. Relies on interaction between web clients (browsers) and web servers. Client initiate requests. Server processes them to return responses.

Question 54

How does HTTP identify resources on the web?

Answer 54

HTTP uses URIs to uniquely identify resources on the web. URIs allow multiple resources to be hosted on a single server by distinguishing them using paths. e.g. example.com/resource1 example.com/resource2

Question 55

What does a GET request do?

Answer 55

Retrieves information from the server Used for reading data Idempotent: repeated requests yield the same result

Question 56

What does a POST request do?

Answer 56

Sends data to the server for processing (form submission, creating a resource) Commonly used for login actions or appending data Non-idempotent: Repeated requests may have different effects (creating multiple resources)

Question 57

What does a HEAD request do?

Answer 57

Similar to GET but only retrieves the headers, not the body Useful for checking meta data (caching or file size)

Question 58

What does a PUT request do?

Answer 58

Stores or replace a resource at the specified URI e.g. Uploading or Updating a file Idempotent: repeated requests result in the same resource state PUT requests explicitly specifies the resource's URI.

Question 59

What does a DELETE request do?

Answer 59

Removes the resource identified by the URI e.g. deleting user account Idempotent: Multiple delete requests have the same effect method may be overridden by human intervention on the origin server.

Question 60

What does a PATCH request do?

Answer 60

Partially modifies a resource. E.g. updating only a user's email in their profile

Question 61

What does an OPTIONS request do?

Answer 61

Returns the communication options available for a resource e.g. checking if a server supports specific methods (e.g. CORS preflight requests).

Question 62

What does a TRACE request do?

Answer 62

Debugging method to see the request as received by the server. Used for diagnostic purposes only (not commonly used).

Question 63

What does a TRACE request do?

Answer 63

Establishes a tunnel to the server. Commonly used for HTTPS traffic through proxies.

Question 64

What is a URI?

Answer 64

A generic term for identifying a resource on the web Can be a URL or a URN URL: Uniform Resource Locator URN: Uniform Resource Name URL: http://ualberta.ca URN: urn:ietf:rfc:3986 Most are URLs

Question 65

What is a URL?

Answer 65

Uniform resource locator Tells you how to get to resource

Question 66

What is a URN?

Answer 66

Uniform Resource Name Tells you the unique name or number given to a resource by some body.

Question 67

What are the two main parts of a URL

Answer 67

Scheme and everything else

Question 68

What are all of the components of a URL

Answer 68

scheme authority -> username:password@ (this is optional) Hostname Port overall sytnax: [username:password@]hostname[:port] then, path query fragment (optional)

Question 69

What does the scheme do in the URL?

Answer 69

Specifies the protocol to access the resource Common Schemes: https, http, mailto, file, data Syntax: scheme://

Question 70

What does the host do in the url?

Answer 70

The domain or IP address of the server

Question 71

What does the port do?

Answer 71

The port # to connect to, i.e :8080 for http, :443 for Https. Optional

Question 72

What does the username@password do in the url?

Answer 72

optional specifies credentials for accessing resource

Question 73

What does the path do in the url?

Answer 73

specifies the location of the resource on the server /index.html in https://ualberta.ca/index.html.

Question 74

what does the query do in the url?

Answer 74

Provides additional parameters for the request ?query=students in https://ualberta.ca/search?query=students

Question 75

What does the fragment do in the url?

Answer 75

Identifies a specific section of the resource https://ualberta.ca/docs#section1 #section1 https://en.wikipedia.org/wiki/Methanol#Applications

Question 76

What is an absolute url?

Answer 76

Specifies complete location of a resource, including: Scheme, authority, path

Question 77

What is a relative url?

Answer 77

Omits part of the abolute url and is interpreted relative to the context.

Question 78

In terms of relative url's What is implied authority, absolute path

Answer 78

starts with / indicating path starts at the root of the domain /images/web-server.svg

Question 79

In terms of relative url's What is implied authority, relative path

Answer 79

Does not start with /, indicating path is relative to the current directory e.g. images/web-server.svg

Question 80

Why are URI's percent encoded?

Answer 80

They must accommodate all kinds of characters. Ensuring diverse resources can be represented on the web.

Question 81

How are URL's encoded in HTTP

Answer 81

Unicode UTF-8 encoded

Question 82

What encoding do we use for domain names

Answer 82

punycode encoding

Question 83

What are the use cases for HTTP POST?

Answer 83

Submitting HTML forms - standard method for sending form data (login, registration) Adding or mutating data - generally used when server is expected to change state (e.g. adding a record to a database, uploading a file)

Question 84

Can HTTP POST include query parameters?

Answer 84

Yes, similar to get, however the payload of the POST request is where most of the data is sent

Question 85

How are POST parameters sent in a POST request?

Answer 85

In POST request body as application/x-www-form-urlencoded or multipart/form-data when uploading files

Question 86

What is multipart/form-data?

Answer 86

A MIME(Multipurpose Internet Mail Extensions) type specified in RFC 2388 Used to send data, especially when a form contains file uploads or binary data breaks the form data into parts, each with its own content headers, allowing binary data and plain text to exist

Question 87

What is multipart/form-data useful for?

Answer 87

file uploads

Question 88

What is the process of using multipart/form-data?

Answer 88

The client sends the content size to the server first, ensuring the server knows what to expect. The server responds with HTTP/1.1 100 Continue if it can handle the specified size. Once acknowledged, the client sends the data in the body of the request.

Question 89

What tradeoff does multipart/form-data introduce?

Answer 89

Increased latency due to the validation step before sending the data body.

Question 90

What are the differences between put and post

Answer 90

POST: sever decides ho\w to process the request and often assigns a new URI to the resource Commonly used for adding new resources, or triggering a server side process PUT: URI itself specifies the resource being modified or created Client takes full control over the resource's location

Question 91

How does the DELETE request work?

Answer 91

Client sends a DELETE request to the server Server removes the resource or marks it for deletion A successful DELETE request doesn't always guarantee that the resource was deleted; it only indicates the server intends to delete it or make it inaccessible.

Question 92

What are the possible server responses to a DELETE request?

Answer 92

200 OK - resource deleted successfully, server may include message in response body 204 No Content - resource deleted successfully, no response body included 202 Accepted - Server has acknowledged the request, but has not yet completed the deletion 404/403 - resource doesn't exist or cannot be deleted.

Question 93

Why is POST less suitable for replacing resources compared to PUT?

Answer 93

POST lacks clear semantics for replacing resources and is not idempotent, unlike PUT.

Question 94

What is the advantage of using DELETE instead of POST for removing resources?

Answer 94

DELETE provides semantic clarity and is idempotent, ensuring repeated requests have the same result.

Question 95

How does PUT align with REST principles?

Answer 95

PUT is tied to the "update/replace" operation, making RESTful APIs more predictable and intuitive.

Question 96

What is WebDAV, and how does it use PUT and DELETE?

Answer 96

WebDAV is an HTTP extension for collaborative file management, relying on PUT to upload files and DELETE to remove them.

Question 97

What is the key distinction between PUT and POST?

Answer 97

PUT targets a specific resource identified by its URI, while POST allows the server to determine the resource's URI.

Question 98

What is an HTTP User agent

Answer 98

The user agent is the software acting on behalf of the user in HTTP communications. Commonly refers to: Web browsers (e.g., Chrome, Firefox, Safari). HTTP clients (e.g., curl, Python’s requests library, Postman). In RFCs, "user agent" often explicitly means a browser but can also include any HTTP client.

Question 99

What is the role of the User Agent?

Answer 99

The user agent initiates HTTP requests to servers and processes their responses.

Question 100

Why is the user-agent important?

Answer 100

It determines the format and features used in HTTP requests. HTTP headers like User-Agent identify the software making the request, enabling servers to adapt responses accordingly.

Question 101

Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/71.0.3578.98 Safari/537.36 What is this user agent?

Answer 101

Chrome 71.0 on Windows 10 on a PC

Question 102

Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:64.0) Gecko/20100101 Firefox/64.0 What is this user agent?

Answer 102

Firefox 64.0 on Windows 10 on a PC

Question 103

Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_2) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/12.0.2 Safari/605.1.15 What is this user agent?

Answer 103

Safari 12 on OSX 10.14

Question 104

Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/64.0.3282.140 Safari/537.36 Edge/17.17134 What is this user agent?

Answer 104

MS Edge 17

Question 105

What is the general structure of a user-agent string?

Answer 105

() Example: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/71.0.3578.98 Safari/537.36

Question 106

What do the 1xx https status codes do?

Answer 106

Indicates the server has received the request and is processing it. Example: 100 Continue — The server has received the request headers, and the client can proceed with sending the request body.

Question 107

What do the 2xx https status codes do?

Answer 107

Confirms the request was successfully processed. Example: 200 OK — The request succeeded, and the server returned the requested data.

Question 108

What do the 3xx https status codes do?

Answer 108

Indicates the client must take additional action (e.g., follow a new URL). Example: 301 Moved Permanently — The resource has been permanently moved to a new location. ** Redirect status codes

Question 109

What do the 4xx https status codes do?

Answer 109

Indicates an error on the client’s side (e.g., bad request). Example: 404 Not Found — The server cannot find the requested resource.

Question 110

5XX — Server Errors:

Answer 110

Indicates an error on the server’s side while processing a valid request. Example: 500 Internal Server Error — The server encountered an unexpected condition.

Question 111

HTTP/1.1 201 Created:

Answer 111

Indicates that the request has succeeded, and a new resource has been created as a result. Typically used with POST or PUT requests.

Question 112

HTTP/1.1 202 Accepted:

Answer 112

The request has been accepted for processing, but the processing is not yet complete. Example use case: A server needs time to process an uploaded file or run a long calculation. The response does not guarantee that the request will ultimately be fulfilled.

Question 113

HTTP/1.1 203 Non-Authoritative Information:

Answer 113

Rarely used. Indicates that the returned information came from a proxy or intermediary, not the origin server. Example use case: A proxy server modifies or filters content before passing it to the client.

Question 114

HTTP/1.1 204 No Content

Answer 114

Indicates that the request was successful, but the server is not returning a message body in the response. Only headers are returned. Useful to use to reduce bandwidth

Question 115

HTTP/1.1 205 Reset Content (rare)

Answer 115

Like 204 No Content but the browser should clear the form/page

Question 116

HTTP/1.1 206 Partial Content

Answer 116

Indicates that the server is delivering part of the resource as requested by the client. Typically used in scenarios like resumable downloads or streaming large files.

Question 117

What does 300 Multiple Choices mean?

Answer 117

The server provides multiple options for the resource, and the client must choose one.

Question 118

When should you use 301 Moved Permanently?

Answer 118

When a resource has been permanently moved to a new URI.

Question 119

What’s the difference between 301 and 302 redirects?

Answer 119

301 indicates a permanent move, while 302 is for temporary redirects.

Question 120

How does a 302 Found redirect affect the address bar?

Answer 120

The address bar remains unchanged, making the redirect invisible to the user.

Question 121

Provide an example of when to use 302 Found.

Answer 121

Redirecting users to a backup server during maintenance.

Question 122

What is the main purpose of 303 see other

Answer 122

Purpose: Designed to solve the forum-posting problem where POST requests (e.g., submitting a form) could accidentally be re-submitted when a user refreshes a page.

Question 123

What does 303 see other do?

Answer 123

The server sends a 303 See Other response with a Location header indicating the new URI. The client is instructed to perform a GET request to the provided URI, instead of resubmitting the original POST request.

Question 124

What happens to the URI in the location bar when a 303 See Other is issued?

Answer 124

The location bar updates to the new URI provided in the Location header.

Question 125

What method is used in the redirected request of a 303 See Other response?

Answer 125

The GET method.

Question 126

HTTP/1.1 307 Temporary Redirect

Answer 126

Go to the URI mentioned in the Location header Keep making requests to this URI you originally requested in case the server needs to redirect you somewhere else next time Cache the redirection using standard caching headers and rules URI in the location bar is updated

Question 127

HTTP/1.1 308 Permanent Redirect

Answer 127

Go to the URI mentioned in the Location header Similar to 301 Moved Permanently Client must repeat the same request for the new location, unlike 301

Question 128

HTTP/1.1 400 Bad Request

Answer 128

Hey buddy, I can't read this garbage. Don't send it again. Request has bad format

Question 129

HTTP/1.1 401 Unauthorized

Answer 129

You have to send authentication information to see this URI. Headers and entity (response body) explains to the browser and user how to log in. Mostly useful for HTTP Authorization: header authentication

Question 130

HTTP/1.1 402 Payment Required (rare)

Answer 130

Pay up, buttercup! Supposedly reserved, but some services use it anyway, e.g. MobileMe used it (the predecessor to iCloud) Google APIs use it YouTube will use it to force you to solve a CAPTCHA

Question 131

HTTP/1.1 403 Forbidden

Answer 131

The web server will never respond to this request, no matter who you log in as Maybe it could answer your request but an administrator disabled that ability.

Question 132

HTTP/1.1 404 Not Found

Answer 132

You've got the wrong resource or path. Can't find what you're looking for. Droids? What droids? Resource cannot be found

Question 133

HTTP/1.1 405 Method not allowed

Answer 133

Whatever method you used (GET/HEAD/POST/PUT/DELETE/...) doesn't work on this URI

Question 134

HTTP/1.1 502 Bad Gateway

Answer 134

The server talks to another HTTP server to fulfill this request and that other server isn't working.

Question 135

HTTP/1.1 503 Service Unavailable

Answer 135

The service is temporarily down. Something's broken and we'll bring it back up eventually. Also used when servers are undergoing maintenance

Question 136

HTTP/1.1 504 Gateway Timeout

Answer 136

The server talks to another process to fulfill this request and that other process isn't responding fast enough. Very common when a webapp is overloaded. Similar to 502, except in this case the packets between the reverse proxy and the origin webserver are just vanishing...