Redes

Chapter 3 – Application Layer Functionality and Protocols

Presentation Primary Functions:
1) Coding and conversion from application
2) Compression
3) Encryption

Session is in charge of maintaining dialogs between source and destination applications

Protocols |
Acronym | Name | Function | Port |
DNS | Domain Name Service | Resolves Internet names to IP addresses | 53 |HTTP | Hypertext Transfer Protocol | Transfer files that make up the web pages | 80 |
SMTP | Simple Mail Transfer Protocol | Transfer mail messages and attachments | 25 |
Telnet | Telnet | Remote access to serves and devices | 23 |
FTP | File Transfer Protocol | Interactive file transfer between systems | 20 and 21 |
POP | Post Office Protocol | In charge of delivering messages to mailbox| 110 |

*Understand Client – Server Model*

*P2P (Peer – to – Peer) Model* Gnutella

DNS
Command line nslookup

Records type
1) A end device address
2) NS Authoritative name server
3) CNAME Full Qualified Domain Name for an alias
4) MX Mail Exchange

SMTP / POP

MUA (Mail User Agent)
* Allows messages to be sent (SMTP)
* Places received messages onclient’s mailbox (POP)

MTA – Mail Transfer Agent
MDA – Mail Delivery Agent

Is the user mailbox on the local server?
* Yes Mail is passed to MDA to be forward to user’s mailbox
* No Mail is passed to MTA to be forward to another server

FTP
Requires TWO connections! (Two ports)

First Connection Port 21 – Control traffic; client-server replies and commands
Second ConnectionPort 20 – Actual file transfer

FTP goes both directions
* Pull (download)
* Push (upload)

DHCP – Dynamic Host Confirmation Protocol

Enables devices on a network to obtain IP address

Without it users must enter manually the IP address, subnet mask and other settings to join the network

Discover Client emits broadcast to all DHCP Servers asking to join a network
Offer All DHCPServers reply with a possible IP address, subnet mask, etc.
Request Client accepts one reply and requests the specific server for it
Acknowledge Specific Server acknowledges and gives the offer to the client

Other Notes (Quizzes)

Secure data traveling between client and server
* HTTPS
* SSH (Secure Shell)

MTA
* Forwards mail between servers
* Recieves mail from clientMDA
* Resolves final delivery issues
* Performs actual delivery to user’s mailbox

MUA
* Client used to access and read email
* Retrieves mail using POP

*Check Wikipedia for TLD (Top level Domains)*
*Check P2P (CISCO material)*

Advantages of client/server model
* Centralized administration
* Security is easier to employ
Properties of P2P
* Acts as bothclient and server
* Hybrid mode includes a centralized directory of files
* Can be used in client server networks

Primary disadvantage of telnet
* Does not support encryption

Characteristics P2P
* Decentralized resources
* Resource sharing without a dedicated server

Microsoft used SMB (Server Message Block) for file sharing

CISCO Version 4 – Chapter 3 Exam

1.What application layer protocol is commonly used to support for file transfers between client and server?
a) HTML
b) HTTP
c) FTP
d) Telnet

2. What are two forms of application layer software? (Choose two)
a) Applications
b) Dialogs
c) Requests
d) Services
e) Syntax

3. A network administrator is designing a network for a new branch office of twenty-fiveusers. What are the advantages of using a client-server model? (Choose two)
a) Centralized administration
b) Does not require specialized software
c) Security is easier to enforce
d) Lower cost implementation
e) Provides a single point of failure

4. What is the purpose of resource records in DNS?
a) Temporarily holds resolved entries
b) Used by the server to...