Application Layer - DNS-Mail Flashcards

Flashcards about Application Layer - DNS-Mail

What is the function of sockets in computer systems?

Sockets are the 'door' between application layer (user space) and transport layer (kernel space).

What is the primary function of the Domain Name Service (DNS)?

It maps human-readable names to computer-friendly IP addresses.

What are the four main elements that comprise the DNS?

Domain name space, DNS database, name servers, and resolvers.

What are some characteristics of domain names?

They are not case sensitive, constituents are separated by '.', can have up to 63 characters per constituent, and up to 255 characters per path.

Name some types of DNS Resource Records (RRs)

Start of authority, IPv4 address of a host, IPv6 address of a host, Mail exchange, Name server, Canonical name, Pointer, Sender policy framework, Service, and Text.

What is the role of root name servers in the DNS hierarchy?

The root servers form the authoritative cluster for enquiries and are contacted by a local name server that cannot resolve a name.

What are the different types of name servers?

Top-level domain DNS servers, other authoritative DNS servers, and local DNS servers.

How does a local DNS server resolve a query if it does not know the answer?

The local DNS queries up the hierarchy to the top-level (root) DNS for the domain and then relays the answer to the resolver client.

What are the main architectural components of email services?

User agents (UA’s/ MUA’s) which allow user to read and send email and Message transfer agents (MTA’s) which transport messages from source to destination.

What are the basic functions of a user agent (mail program)?

Compose, report, display, dispose.

What are the main components of the RFC 2822 standard for text message format?

Header lines and body.

What are the three phases of an SMTP transfer?

Handshaking, transfer of messages, and closure.

What are the five additional message headers that MIME adds?

MIME-Version, Content-Description, Content-Id, Content-Transfer-Encoding, and Content-Type.

What protocols are used for message transfer and access?

SMTP, POP3, IMAP, and HTTP.

List some audio MIME content subtypes

Basic, mpeg, mp4

What is a primary function of IMAP?

IMAP keeps user state across sessions.

What are the three states of a POP3 transaction?

Authorisation, Transactions, Update.