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Layer 7 Protocols
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- 1What is the characteristic of HTTP?HTTP(HyperText Transfer Protocol) is an application-layer protocol for distributed, collaborative hypermedia information systems. It usually uses TCP port 80 and presumes an underlying reliable transport layer, but it can also use UDP for services (Voice...). HTTP resources are identified and located on the network by Uniform Resource Identifiers (URI) using the http URI schemes. HTTP is a stateless protocol, but state can be added using cookies or URI encoded parameters.
- 2What is the characteristic of HTTPS?HTTPS is a combination of HTTP and SSL/TLS to prevent eavesdropping and to securely identify a webserver. The user trusts the certificate authority to vouch only for legitimate websites without misleading names. HTTPS uses port 443.
- 3What is the characteristic of SOAP?SOAP(Simple Object Access Protocol) is a messaging protocol for exchanging structured information between web services and computer networks.
A protocol for XML-based data exchange. It is not tied to a specific transport (ftp, http, mail, etc.). Mostly used with HTTP on top of TCP. The envelope encapsulates the whole SOAP message and defines what is in the message and how to process it. The message itself consists of an optional header and a mandatory body. The body contains the request or response message. The header contains: namespace definitions, digital signatures or can be used to specify an account number for pay-per-use SOAP services. Because of the verbose XML format, SOAP can be considerably slower than competing middleware technologies such as CORBA.
SOAP is often used where direct access to foreign systems is not desired because of compatibility or security reasons. Limitation of how and to which extent something is accessible is possible. - 4What are HTTP persistent connections?In HTTP/0.9 and 1.0, the connection is closed after a single request/response pair. In HTTP/1.1 a keep-alive-mechanism was introduced, where a connection could be reused for more than one request. Such persistent connections reduce request latency perceptibly, because the client does not need to re-negotiate the TCP 3-Way-Handshake connection after the first request has been sent.
Also known as HTTP keep-alive, is the idea of using a single TCP connection to handle multiple HTTP requests, as opposed to opening up a new connection for every request.
Keep a connection to a web-server open so it doesn't need to do another Handshake with the server again. The idea behind it that requests/responses are faster with an already opened connection. - 5What is the purpose of HTTP Headers?HTTP headers allow the client and the server to pass additional information with the request or the response. An HTTP header consists of its case-insensitive name followed by a colon ':', then by its value (without line breaks). Leading white space before the value is ignored.
General header: Headers applying to both requests and responses but with no relation to the data eventually transmitted in the body.
Request header: Headers containing more information about the resource to be fetched or about the client itself.
Response header: Headers with additional information about the response, like its location or about the server itself (name and version etc.).
Entity header: Headers containing more information about the body of the entity, like its content length or its MIME-type - 6What are the categories of HTTP error codes?1xx Informational (100 Continue, 101 Switching protocols, 102 Processing)
2xx Success (200 OK, 201 Created, 202 Accepted, 203 Non-Authoritative Information, …)
3xx Redirection (300 Multiple Choices, 301 Moved Permanently, 303 See Other, 304 Not Modified)
4xx Client Error (400 Bad Request, 401 Unauthorised, 403 Forbidden, 404 Not found)
5xx Server Error (500 Internal Server Error, 501 Not Implemented, 503 Service Unavailable) - 7Which are the different request methods in HTTP?There are different request methods:
- HEAD request a resource but server only returns the HTTP header response and no response body
- GET requests a a specific resource.
- POST submits data to be processed to the identified resource. The data is included in the body of the request
- PUT uploads a representation of the specified resource
- DELETE deletes specified resource
- TRACE echoes back the received request
- OPTIONS returns the HTTP methods that the server supports for a specified URL.
- CONNECT converts the request connection to a transparent TCP/IP tunnel, usually to facilitate SSL encrypted communication through an unencrypted HTTP proxy
- PATCH apply partial modifications to a resource - 8What does a HTTP request message consist of?The request message consists of the following:
- A request line (e.g., GET /images/logo.png HTTP/1.1, which requests a resource called /images/logo.png from the server).
- Request header fields (e.g., Accept-Language: en).
- An empty line.
- An optional message body. - 9What does a HTTP response message consist of?The response message consists of the following:
- A status line which includes the status code and reason message (e.g., HTTP/1.1 200 OK, which indicates that the client's request succeeded).
- Response header fields (e.g., Content-Type: text/html).
- An empty line.
- An optional message body. - 10Which party initiates the SSL handshake?A client by sending a "client hello" message that lists cryptographic information such as the SSL or TLS version and, in the client's order of preference, the CipherSuites which it supports.
Client ---Hello. those are my encryption---→ Server
Client <---- Hello back, this is the procedure + Cert — Server
Client <-----Server Key Exchange Message ----- Server
Client ---- Client Cert is presented --→ Server
Client ---- Client Key Exchange --→ Server - 11What is FTP over HTTP?FTP over HTTP is the name used to refer to a specific type of HTTP traffic between a web browser and an explicitly configured proxy. For the most part, it is like any other HTTP request. The distinguishing factor is that the requested resource resides on an FTP server rather than an HTTP server. Correspondingly, this means an FTP over HTTP request will contain a URL prefixed with "ftp://" instead of "http://" and the HTTP "Host" header value will include port 21 (instead of no port number at all, in which case port 80 is assumed).
- 12Name common L7 protocolsTelnet, FTP, HTTP, SMTP
- 13Give two examples of how an application can use HTTP headers.HTTP header can be used to communicate the User-Agent, which tells the server what OS and Browser client is using. Accept-Language, which sends the list of acceptable human languages for the response.
Authorization headers: to specify Authentication credentials for HTTP authentication.
To define Cookies to maintain a session with a server, since HTTP is sessionless.
Set a Cookie (Set-Cookie:)
If a Proxy is used (X-Forwarded-For:)
To keep the connection alive (Keep-Alive) - 14—
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- Informatik Fichas sobre Layer 7 Protocols, creado por Simon Perez el 05/12/2019.
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