3.3 Application Layer Protocols And Services

Question 1

Application Laters Protocols and Services

Answer 1

• The transport layer uses an addressing scheme called a port number
• Port numbers identify applications and application layer services that are the source and destination of data
• Server programs generally use predefines port numbers that are commonly known by clients

Question 2

Services

Answer 2

• Domain Name System (DNS): TCP/UDP port 53
• HTTP: TCP port 80
• SMTP: TCP port 25
• Post Office Protocol (POP): UDP port 110
• Telnet: TCP port 23
• DHCP: UDP port 67
• FTP: TCP ports 20 & 21

Question 3

DNS Services and Protocol

Answer 3

• Domain names were created to convert the numeric IP address into a simple, recognizable name
• DBS was created for domain name—to—address resolution of networks
• DNS uses a distributed set of servers to resolve the names associated with the numbered addresses
• Devices are usually given 1 or more DNS Server addresses that they can use for name resolution
• Uses different types of resource records to actually resolve the name/IP address issues
• The number is returned ti the client for use in making requests of the server

Question 4

How DNS Works

Answer 4

• The DNS protocol
• The DNS resolver

Question 5

The DNS protocol

Answer 5

• Defines an automated service that matches resource names with the required numeric network address
• Includes the format for queries, responses, and data formats

Question 6

The DNS resolver

Answer 6

• Supports name resolution for the other network applications and other services that need it
• When a user’s application requests to connect to a remote device by name, the requesting DNS client queries one of these DNS servers to resolve the name to a numeric address.

Question 7

Name Resolution and Caching

Answer 7

• A DNS server provides the name resolution using the name daemon, which is often called named (pronounced name-dee)
• DNS server act as the phonebook for the Internet
• DNS server stores, different types of resource records used to resolve names

Question 8

Record types

Answer 8

• A: An end device address
• NS: An authoritative name server
• CNAME: The canonical name (or fully qualified domain name[FQDN]) for an alias; used when multiple services have the single network address, but each service has its own entry in DNS
• MC: Mail exchange record; maps at domain to a list of mail exchange servers for that domain

Question 9

DNS hierarchy

Answer 9

• DNS uses a a hierarchical system to create a database to provide name resolution
• the top of the hierarchy, the root servers maintain records about how to reach the top-level domain servers, intern have records that point to the secondary-level domain servers and so on
• The different top level domains represent either the type of organization or the country of origin. The following are examples of top level domains:
  
  • .au: Australia
  • .co: Colombia
  • .com: A business or industry
  • .jp: Japan
  • .org: A nonprofit organization