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Similar to DNS (1).pptx computer networking access DATA
DNS (1).pptx computer networking access DATA
- 31. Address Resolution Mapping nameto an address or an address to a name is called name-address resolution. RESOLVER • DNS is designed as a client -server application. • A host that needs to map an address to a name or a name to an address calls a DNS client called a resolver. • The resolver accesses the closest DNS server with a mapping request. • If the server has the information it satisfies the resolver ;otherwise, it either refers the resolver to other servers or asks other servers to provide the information. • After the resolver receives the mapping, it interprets the response to see if it is a real resolution or an error, and finally delivers the result to the process that requested it.
- 32. Mapping Names toAddresses • In this case, the server checks the generic domains or the country domains to find the mapping. • If the domain name is from the generic section, the resolver receives a domain name such as “chal .atc: fhda.edu”. • The query is sent by the resolver to the local DNS server for resolution. • If the local server cannot resolve the query, it either refers the resolver to other servers or asks other servers directly. • If the domain name is from the country domain section, the resolver receives a domain name such as “ch .fhda.cu.ca.us”. The procedure is the same.
- 33. Mapping Addresses toNames • A client can send as IP address to a server to be mapped to a domain name. This is called a PTR query. • To answer queries of this kind, DNS uses the inverse domain. • However, in the request, the IP address is reversed and two labels, in- addr and arpa are appended to create a domain acceptable by the inverse domain section. • For example. if the resolver receives the IP address 132.34.45.121 , the resolver first inverts the address and then adds the two labels before sending. the domain name sent is “121.45.34.132.in- addr.arpa” , which is received by the local DNS and resolved.
- 34. A resolution canbe of two types – iterative and recursive.
- 35. Caching Mechanism • Inboth iterative and recursive resolution, after a server asks for a mapping request from another server, it receives the response and stores this information in the Cache memory before sending it to the client. • This is done to lower the search time it takes for a server to check the IP Address in its Database. • So, the next time, if a request comes to the server, it first checks its cache memory and tries to resolve the request.
- 36. Electronic mail (e-mail) •Electronic mail (e-mail) is a computer-based program that allows users to send and receive messages. • Email information is transmitted via email servers and uses a variety of TCP/IP protocols. • For example, the simple mail transfer protocol (SMTP) is a protocol that is used to send messages.
- 37. • Components OfElectronic Mail • The following are the essential components of an e-mail system: • User Agent (UA) • Message Transfer Agent (MTA) • Message Access Agent (MAA)
- 38. User Agent (UA) •The User-Agent is a simple software that sends and receives mail. It is also known as a mail reader. • It supports a wide range of instructions for sending, receiving, and replying to messages and manipulating mailboxes. • Some of the services supplied by the User-Agent are listed below: • Reading a Message • Sending a reply to a Message • Message Composition • Forwarding a Message • Handling the Message
- 39. Message Transfer Agent •The Message Transfer Agent manages the actual e-mail transfer operation (MTA). • Simple Mail Transfer Protocol sends messages from one MTA to another. • A system must have a client MTA and a system MTA to send an e-mail. • If the recipients are connected to the same computer, it sends mail to their mailboxes. If the destination mailbox is on another computer, it sends mail to the receiver's MTA.
- 40. Message Access Agent •The Simple Mail Transfer Protocol is used for the first and second stages of e-mail delivery. • The pull protocol is mainly required at the third stage of e-mail delivery, and the message access agent is used at this point. • POP3(Post Office Protocol) and IMAP4(Internet Message Access Protocol) are the two protocols used to access messages.
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- 42. First Scenario • Inthe first scenario, two user agents are required. The sender and recipient of the e-mail share the same machine directly connected to the server. • For example, let us consider two user agents, Ninja1 and Ninja2. When Ninja1 sends an e-mail to Ninja2, the user agent (UA) programme is used to prepare the message. Following that, this e-mail gets saved in the Ninja2 inbox.
- 43. Second Scenario • Inthis case, the sender and recipient of an e-mail are essentially users on two different machines over the internet. User-Agents (UA) and Message Transfer Agents(MTA) are required in this scenario. • For example, two user agents (Ninja1 and Ninja2), as illustrated in the diagram. When Ninja1 sends an e-mail to Ninja2, the user agent (UA) and message transfer agents (MTAs) programmes prepare the e-mail for transmission over the internet. Following that, this e-mail gets stored in Ninja2's inbox.
- 44. Third Scenario • Thesender is connected to the system by a point-to-point WAN, which can be a dial-up modem or a cable modem in this case. On the other hand, the receiver is directly attached to the system, as it was in the second scenario. • The sender also needs a User agent (UA) to prepare the message in this situation. After preparing the statement, the sender delivers it over LAN or WAN via a pair of MTAs.
- 45. Fourth Scenario • Inthis scenario, the recipient is linked to the mail server via WAN or LAN. • When the message arrives, the recipient must retrieve it, which needs additional client/server agents. • This scenario requires two user agents (UAs), two pairs of message transfer agents (MTAs), and a couple of message access agents (MAAs).
- 46. MIME: Multipurpose Internet MailExtensions (MIME) is a standard that extends the format of email messages to support text in character sets other than ASCII, as well as attachments of audio, video, images, and application programs. • The MIME format is used in emails to support multimedia and non-ASCII data types for transmission. • The MIME format is a standard framework that enables the user to attach multiple data types like text, images, audio, etc., within emails using headers like Content-type, content-disposition, content-type- encoding, etc.