3. Application Layer Flashcards
List out the upper 3 layers in OSI model
- Application
- Presentation
- Session
What does the application layer provides?
- Provides the interface between the application used to communicate, and the underlying network over which messages are transmitted
List out the application layer protocols ( 5 )
- HTTP ( Hypertext Transfer Protocol )
- FTP ( File Transfer Protocol )
- TFTP
- IMAP ( Internet Message Access Protocol )
- DNS ( Domain Name System )
What are the 3 primary function in the presentation layer?
- Formatting, or presenting, data at the source device into a compatible format for receipt by the destination device
- Compressing data in a way that can be decompressed by the destination device
- Encrypting data for transmission and decrypting data upon receipt
What are the functions in the session layer? ( 2 )
- It creates and maintains dialogs between source and destination applications
- It handles the exchange of information to initiate dialogs, keep them active, and to restart sessions that are disrupted or idle for a long period of time
What layer protocols are used by both the source and destination devices during a communication seesion?
- Application Layer Protocols
What must be done for the communication to be successful?
- The application layer protocols that are implemented on the soure and destination host must be compatible
What does TCP/IP application protocols do?
- Specify the format and control information necessary for many common internet communication functions
What does DNS ( Domain Name Search )do? Also list out the port
- Translates domain names ( youtube.com ), into IP Addresses
2.TCP, UDP client 53
*UDP 53 - Typically used for most DNS queries because it’s faster (connectionless).
*TCP 53 - Used when the response data size exceeds 512 bytes or for zone transfers between DNS servers.
What does DHCP ( Dynamic Host Configuration Protocol ) do? Also list out the port
- Dynamically assigns IP addresses to be re-used when no longger needed
- UDP client 68, UDP server 67
*Client UDP 68: When a device (like a computer or phone) joins a network, it sends a request (via UDP) to ask for an IP address on port 68.
* Server UDP 67: The DHCP server listens on port 67 to respond to those requests and assigns IP addresses.
What does HTTP do? Also list out the port
- A set of rules for exchanging text, graphic images, sound, video and other multinedia files on the World Wide Web
- TCP 80 , 8080
- Port 80: The standard port for HTTP (non-secure) communication over TCP.
- Port 8080: Sometimes used as an alternative to port 80, especially for web servers running on a machine where port 80 is already in use or for testing purposes.
What is the requesting information’s device called?
- Client
What is the responding the request’s device called?
- Server
- Application layer protocols describe the format of the requests and responses between clients and servers
What can pear-to-pear network do for 2 or more computers?
- Connected via a network and can share resources without having a dedicated server
What layer does client and server processes are considered to be in?
- Application Layer
What can an end device ( peer ) function in pear-to-pear ( 2 )
- Server
- Client
- One computer might assume the role of server for one transaction while simultaneously serving as a client for another. The roles of client and server are set on a per request basis
List out the common P2P network ( 4 )
- BitTorrent
- Direct Connect
- eDonkey
- Freenet
List out the 3 parts that the browser interprets
- HTTP / HTTPS ( Protocol / Scheme )
- www.youtube.com ( server name , URL )
- index.html ( Specific filename requested )
- HTTPS has log
List out the steps on how the web browser and web server interact
- Browser interprets 3 parts of the URL ( http , www , index.html )
- Checks the name server to convert into numeric IP address, then sending a GET request to the server and asks for the index.html file
- In response to the request, the server sends the HTML code for this web page to the browser
- The browser deciphers the HTML code and formats the page for the browser window
What is HTTP?
- Is a request / response protocol specifies the message types used for that communication
List out 3 common messages types of HTTP
- GET
- Request data
- POST
- Uploads data files ( form data )
- PUT
- Uploads resources or content to the web server ( image )
What is Email?
- Is a store-and-forward method of sending, storing, and retriving electronic message across a network
Email messages stored in where?
- In databases on main servers
List out the email protocols ( 2 )
- Send Mail
- Simple Mail Transfer Protocol ( SMTP )
- Receive Mail
- Post Office Protocol ( POP )
- IMAP
What is the main function of SMTP?
- Send the email to the server using port 25
- Port 25 is important
- It may send to other server
What are the formats for SMTP message?
- Message Header
- Email Address
- Sender Email Address
- Message Body
What is the main function of POP?
- Sends a request to establish a TCP connection with the server using port 110
List out the steps for SMTP ( 4 )
- Connection is made
- Client attempts to send the email to the server across the connection
- When the server received the message, it either places the message in a local account, if the receipent is local, or forwards the messages to another mail server for delivery
- The destination email server may not be online or may be busy. If so, SMTP spools messages to be sent at a later time
Why POP is not recommend for small business
- Because POP does not store messages, it is not recommended for small business that need a centralized backup solution
List out the steps for POP ( 3 )
- When a client wantes to make use of the service, it sends a request to establish a TCP connection with the server
- When the connection is established, the POP server sends a greeting
- The client and POP server then exchange commands and respons until the connection is closed or aborted
What is the main function of IMAP?
- Is another protocol that retrive email messages from the server ( Same as POP )
What is the difference between POP and IMAP? ( 2 )
- IMAP will copy the message then sends to the client application and the original messages are kept on the server until manually deleted
- While POP message data will be deleted on the server after the client receives mail using POP
What will happen if a user decides to delete a message using IMAP ?
- The server synchronizes that action and deletes the message from the server
What is an example and an advantage for Fully-qualified domain names?
- https://www.youtube.com
- Are much easier for people to remember
What does the DNS server stores? ( 3 )
- Name
- Address
- Type of Record
List out some of the records types ( 4 )
- A
- An end devie IPv4 address
- NS
- An authoritiative name server
- AAAA
- An end device IPv6 address
- MX
- A mail exchange record
What does DNS protocol provides?
- Defines an automated service that matches resource names with the required numeric network address
- Includes the format for queries, responses and data
Why are domain names were created?
- To convert numeric IP addresses into a simple, recognizable name
What are the step that the DNS process
- The local DNS server first looks at its own records
- If it was unable to resolve the name by using its stored records, it contacts other servers to resolve the name
- After the match is found and returned to the original requestion server, the server temporily stores the numbered address in the even that the same name is requested again
List out the DNS message section and a basic description
- Question
- Question for the Name server
- Answer
- Resource records answering the question
- Authority
- Resource records pointing toward an authority
- Additional
- Resource records holding additional information
Why DNS uses hierarchial system?
- Create database to provide name resolution
List out the examples of top-level domains
- .com - business or industry
- .org - a non-profit organization
- .au - Australia
What is the role of DNS server?
- Maintains a specific database file and is only responsible for managin name-to-ip mappings for that small portion of the entire DNS structure
What will happen when a DNS server receives a request for a name transalation that is not within its DNS zone?
- The DNS server forwards the request to another DNS server within the proper zone for translation
What is the nsloopup command?
- A computer operating system utility that allows a user to manually query the DNS servers configures on the device to resolve a given host name
What can nslokup also be used?
- Used to troubleshoot name resolution issues and to verify the current status of the name servers
What will happen when the nslookup command is issued?
- The default DNS serer configured for your host is displayed
What can be entered at the nslookup prompt?
- Host
- Domain
What is the purpose of Dynamic Host Configuration Protocol ( DHCP )
- Automates the assignment of IPv4 address, subnet masks, gateways and other IPv4 networking parameters
- Auto assign IP address
What is static addressing?
- Manually entering IP address information
- Static IP addressing
List out the examples of dynamic addressing?
- Dynamic Host Configuration Protocol ( DHCP )
When is using DHCP addressing?
- General purpose hosts ( end user devices )
When we use static addressing? ( 4 )
Network Devices
1. Routers
2. Switches
3. Servers
4. Printes
What does DHCPv6 provides?What it doesn’t provide ? ( 2 )
Provide Similiar Services Like DHCP
1. Automates the assignment of IPv6 address, subnet masks, and other IPv6 networking parameters
Doesn’t Provide :
1. Default Gateway Address
- It can only be obtained dynamically from the router advertisement message of the router
List out the DHCP Process
- D - Discover ( DHCPDISCOVER )
- Identify any available DHCP servers on the network
- O - Offer ( DHCPOFFER )
- Offers a lease to the client
- R - Request ( DHCPREQUEST )
- Identifies the explicit server and lease offer that the client is accepting
- A - Acknowlwdgement ( DHCPACK )
- Acknowledge message and begin a new DHCPDISCOVER message
Why was File Transfer Protocol developed?
- Was developed to allow for data transfer between a client and a server
- FTP cilent is an application which runs on a computer that is being used to push and pull data from FTP
List out the step for FTP ( 3 )
- The client establishes the first connection to the server for control traffic using TCP port 21
- Consists Clients
- Server Replies
- The client established the second connection to the server for the actual data transfer using TCP port 20
- It was created every time there is data to be transferred
- The data transfer can happen in either direction, the client can pull ( download ) data from the server, or push ( upload ) data to the server
List out the 3 functions of SMB messages
- Start, authenticate, and terminate sessions
- Control file and printer access
- Allow an application to send or received messages too or from another device
What is Server Message Block ( SMB )?
- A client / server, request-response file sharing protocol
What are the difference between FTP and SMB?
- Clients establish a long-term connection to servers ( SMB )
- They can access the resources on the server as through the resource is local to the client host
