IWP HTML and HTTP HTML5 - Define semantics of content and structure of a hypertext document Markup <!DOCTYPE> - Defines the document type <html> - Elementet er rodelementet i en html-side. <head> - Contains metadata/information for the document <input> - Defines an input control <meta> - Defines metadata about an HTML document <script> - Defines a client-side script <!--...--> - Defines a comment Attributes name - bruges til at henvise til form data, efter at formen er blevet sendt, eller til at henvise til elementet i et script. HTTP Header. Efter \r\n Er det hvad der bliver sendt. Request Header Name Description Host The domain server Connection Control options for the current connection and list of hop-by-hop request fields. ContentLength The length of the request body in octets Name Description Accept Media Types that is/are acceptable for the response. (text/html, Json, e.t.c) Authorization Authentication credentials for HTTP Authentication User-Agent The user agent : Browser ContentType Origin Referer AcceptEncoding AcceptLanguage The Media Type of the body request (Used with POST or PUT) Initiates a request for cross-origin resoruces sharing (Asks server for Access-Control-* response) This is the address of the previous web page from which a link to the currently requested page was followed List of acceptable encodings, gzip, deflate List of acceptable human languages for response Response Header Name CacheControl Description Tells all caching mechanisms from server to client whether they may cache this object. It is measured in seconds Server A name for the server Date The date and time that the message was sent ContentType The MIME Type of the content TransferEncoding The form of encoding used to safely transfer the entity to the user Connection Control options for the current connection and list of hop-by-hop response fields. Example Name Description Expires Gives the date/time after which the response is considered stale X-XSSProtection Cross-Site-Scripting (XSS) filter AccessControlAllow-Origin Example Specifying which web sites can participate in crossorigin resource sharing StrictTransport- A HSTS Policy informing the HTTP client how long to cache the HTTPS only policy and whether this applies Security to subdomains. X-PoweredBy Specifies the technology supporting the web technology, PHP/7.0, ASP.NET .. e.t.c. HTTP Stateless Protocol: Web Sockets REST Computer Networks and the Application layer Internet protocol stack Number Name Inside 5 Application layer HTTP, DNS, SSH, TLS 4 Transport Layer UDP / TCP 3 Network layer IP (IPv4, IPv6), IPsec 2 Link layer Ethernet & WiFi 1 Physical layer Ethernet Cable Device Layer End-system Application, Transport Device Layer Router Network Switch Network Client Server Paradigm Server Always-on host Permanent IP Address Often in data centers, for scaling Client Contact, communicate with server (Doesn't run all the time) May be intermittently connected May have dynamic IP addresses Do not communicate directly with each other Application Layer In the application layer we have HTTP, DNS, SSH and TLS.... HTTP HTTP uses TCP: Client initates TCP connection (creats socket) to server, port 80. Server accepets TCP connection from client HTTP messages (application-layer protocol messages) exchanged between browser (HTTP client) and web server (HTTP server) TCP connection closed HTTP is "sateless" Server maintains no information about past client requests. HTTP connection: Two types Non-persistent Persistent Non-persistent HTTP TCP connection opended At most one object sent over TCP connection TCP connection closed Persistent HTTP TCP connection opened to a server Multiple objects can be sent over single TCP connection between client and that server TCP connection closed DNS DNS hierachial database. Name Order Root 1 TLD (Top Level Domain) 2 Authoriative 3 There are DNS lookup recursive and iterative. Iterative Client will ask the Local name server, if the local name server does not know it, it will ask in a hierachial order. And the asked servers will respond to the local name server. Recursive Burden of name resolution on contacted name server DNS Records Type = A Name is hostname value is IP Adress Type = CNAME Name is alias name for some real name. google.com might be server510.google.com Type = NS Name is domain Value is hostname of authoriative name server for this domain Type MX Value is name of mailserver associated with name Reliable Data Transfer and the Transport Layer Reliable Data Transfer Noiseless Channelse Stop-And-Wait Noisy Channels Stop and Wait ARQ (Automatic repeat query) Go Back N ARQ Selective Repeat ARQ Transport layer TCP (Transmission Control Protocol) A TCP socket is identified by the source IP address, the source port, destination address, and the destination port, TCP establishes bi-directional full-duplex session between the sender and the receiver. TCP Header: 20 bytes Three-Way-Handshake Point-to-point One sender, one reciever reliable transport between sending and receiving process flow control - Sender won't overwelm receiver Congestion control - Throttle sender when network overloaded Does not provide: timing, minimum throughput guarantee, security Connetion-oriented: Setup required between client and server processes Full-duplex Bi-directional data flow in same connection MSS: maximum segment size. TCP Segment structure. TCP Sender TCP Receiver TCP Retransmission scenarios TCP Flow control Three way handshake Congestion Control UDP (User Datagram Protocol) A UDP socket is fully identified by the destination IP adress and the destination port. UDP Header: 8 bytes No connection to create and maintain Packet can arrive out of order Unreliable data transfer - between sending and receiving process Does not provide: reliability, flow control, congestion control, timing, throughput gurantee, security or connection setup. Network Security Cryptography Plaintext -> encryption algorithm (and Alices key) -> Cipher text -> decryption algorithm (and bobs decryption key) -> plaintext Symmetric Key Cryptography Encryption & Decryption key is the same. Public Key Cryptography / Asymetric Public key bliver brugt til at kryptere med. Private key bliver brugt til at dekryptere med
