Topic #10: Application Layer Services and Examples Flashcards
These identify applications and application layer services that are the source and destination of data
Port Numbers
What addressing scheme does the transport layer use?
Port Numbers
Port Number for the Domain Name System
TCP/UDP port 53
Port Number for HTTP
TCP port 80
Port number for SMTP
TCP port 25
Port number for POP
UDP port 110
Port number for Telnet
TCP port 23
Port number for DHCP
UDP port 67
Port for FTP
TCP Ports 20 and 21
Two things that make DNS Work
DNS Protocol and DNS Resolver
This defines the automated service that matches the resource names with the required numeric network address
DNS protocol
This supports the name resolution for the other network applications and other services that need it
DNS resolver
Record type that means an end device
A
Record type which means an authoritative name server
NS
Record type that is a canonical name for an alias
CNAME
Record type that means Mail Exchange Record
MX
Steps in using WWW Service and HTTP
- URL is typed in the address bar
- browser checks with the DNS server and converts it to an IP address
- Connects to the server requested
- Using HTTP the browser sends a GET request for the desired HTML document
- the server sends the HTML for the webpage
- browser interprets the HTML code and formats the page
The email client when people compose e-mails.
Mail User Agent
Applications and services for MUA to use
POP or POP3
SMTP
What protocol to use when Sending email?
SMTP Protocol
What protocol to use when receiving emails?
POP Protocol
This is used to forward emails, receives emails from the Mail User Agent, uses SMTP to route emails between servers and passes email to the MDA for final delivery
Mail Transfer Agent
Receives messages from MUA or from the MTA on another server
Mail Delivery Agent
Command in the SMTP protocol that identifies the SMTP client process to the SMTP server process
HELO
Command in the SMTP protocol that is a newer version of HELO
EHLO
Command in the SMTP protocol that identifies the sender
MAIL FROM
Command in the SMTP protocol that identifies the recipient
RCPT TO
This is another commonly used application layer protocol that was used to develop to allow file transfers between client and a server
File Transfer Protocol
Command in the SMTP Protocol that identifies the body of the message
DATA
FTP Process
- Client opens first connection to the server for control traffic
- Client opens second connection for control traffic
- Gets data
this protocol enables devices to obtain IP addresses, subnet masks, gateways, DNS server information and etc.
Dynamic Host Configuration Protocol
DHCP IP address hosting process
- assigns an IP address that is not being used from a range of available IP addresses
- if host logs off or losses power, IP address is returned to the pool to be reassigned to another host if needed
This protocol allows servers to share their resources with clients
Server Message Block
What SMB does
-start, authenticate and terminate sessions
- control file and printer access
- allow applications to send/receive messages to/from another device
Gnutella protocol packet type for device discovery
ping
Gnutella protocol packet type as a reply to a ping
pong
Gnutella protocol packet type for a file location
query
Gnutella protocol packet type as a reply to a query
query hit
Gnutella protocol packet type as a download request
push
Disadvantage of using Telnet Service
Data is not encrypted
Oldest application layer protocols
Telnet
Secure version of Telnet
Secure Shell (SSH)
This protocol allows users to emulate text-based terminal devices over the network using network software
Telnet
Telnet Protocol Command that enables the user to request that a response appear on the terminal screen to indicate that the VTY session is active
AYT (Are You There)
Telnet Protocol Command that deletes all text from the current line
EL (Erase Line)
Suspends the process to which the virtual terminal is connected.
IP (Interrupt Process)
These are computer programs with which the user interacts and initiate data transfer process at the user’s request
Applications
These are background programs that provide the connection between application layer and the lower layers of the networking model
Services
It allows P2P applications to search for shared resources on peers
Gnutella
These were created to convert the numeric IP addressed into a simple, recognizable name
Domain Names
