Papers

MAIL SERVER

A mail server is an application that permits you to send messages from an user to any other user regardless of the net where the users are. The mail server also is named MTA (mail transport agent), it transports the mail to the MTA of destination using SMTP (Simple Message Trasfer Protocol).

Then MTA receives the mail and sends it to a mail deliver agent (MDA) which puts the e-mail in storage while the user accepts the mail. POP3 is a mail local client to get emails stored in a remote server to our server. IMAP is an access protocol to stored messages in a server. You can access to your mail with imap from a anywhere. The message is genereted in the client side by the MUA application, the MUA sends the message to its local MTA, the local MTA searches its registers, if the destination is registered, it sends the message immediately to its MDA, which stores the message until the user access it using POP3 or IMAP protocols. For this reason the mail server is named pop server or imap server, according the used protocol. The mail server uses ldap for user authentication and stored information in it, also implements ssl /tls for traffic encryption to provide secure pages for the users. The server uses anti-spam system to detect and delete all the mails that the user doesn't want and also uses an anti-virus system to find bad programs.

Security

There aren`t any security server 100% secure one form to secure the net against electronic attacks from out is to separate the net of other nets and systems. The security servers have an adequate level of security to connect the net with other nets. a solid secure server has a limited value if there are weak points in the net, for this reason it is necessary use security in all the components of the net and to plan a security policy that takes into account the risks of each component. The principal features for the mail server 1 set and apply the adequate level to guarantee email servers install a firewall to avoid access non authorized in the net use security protocol ip version 6 to avoid the mail traffic don't connect the mail server to Internet if there is no a firewall configured

2 set and apply the authentication method pop3 standard authentication service of users send authentication information to mail server in plain text, so the password to connect the mail server and client is encrypted, this avoids access denied.

WEB APLICATION

The users can access to a web application thanks to a web server on Internet. A web server is software that reply web pages when an user is using a browser. A user generates a request when the user clicks in a link or write a URL in a browser. Previously, users can not interact with information found by browsers because the pages were static or just simple documents in html. A static web page doesn't change when you request it, the web server sends the page to a web browser without editing allowed. The building of html documents had change from the first wrote page in html stored in a folder in the web server to dynamic pages. the dynamic pages ere edited before submit the page to the client browser

How does a web application really work?

When a web browser receives a request to show a static web page, the server only sends the page to the client browser. when a web browser sends a request looking for a dynamic web page to a server, the server find the page and send it to the application server which passes the page to the browser changing it according to the user actions.

How does the web application access the database?

An application server can not access the database because the format doesn't let decrypt data. the application server only can connect with the database thanks to controller that work between the database. this software works as an interpreter between application server and database the controller sets connections with the database and builds a series of registers.

This series of registers are sets of data extracted from a database , it is returned to the application server , it uses the data to complete the page an application server let to work with resources of the sever , like database , for example , a dynamic page can indicate to application server to extract data from a database and insert it in code html of the page the instruction to extract data from a database is named database query, a query requires a search expressed in a database language called SQL (structured query language) the sql query is written in scrips or tags in the server that has the page. We can use practically any database with web application as long as the database controller is installed right in the server, if we want to develop applications for Enterprise client, we can use a database based on servers as SQL server, oracle or MYSQL. If the database is located in a web server we must secure a connection available and fast between systems for looking a web application run fast and efficiently advantages of web applications

You can access from anywhere, we only need connection and a web browser if you open source tools, you don't pay to use the operative system Linux, Apache web server, the php language or mysql database engine, it is not necessary to pay for tools used by users easy authentication .just make changes to the server online it is an multi platform application, so, the user can use the program using windows Macintosh or other system, the most necessary is a web browser.

SNMP Simple Network Management Protocol developed in august of 1988 by case, MCcloghric, rose and waldbusser, as a solution to the problem of communication of different networks. It gives the capacity to audit and communicate status communication among huge verify of hosts. It is useful on large networks and where demands the vitality of the network. SNMP is as protocol of application layer that belongs to the TCP/IP family and it serves for managing of data, It’s based on packages, UDP, it means, it’s connectionless defining a server-client connection between the networks manager (client) and the managed elements (servers, active devices) called agents.

SNMP COMPONENTS: Agents: Called the “clients” It means, are the equipments or devices, that make part of the network and when are monitored (Work station, routers, switches). NMS: Network Management Station, It’s the device where it’s located the monitoring software, meaning the “Server” that allows us the monitoring of the network and where stores all collected information. MIB`s: Management Information Base, It’s the logical database that the NMS and networks device (Agents), keep, where we found the information of the components of each of these devices. This database hierarchy structured and contains the OID (Object Identify)

There are 2 MIB versions, which are: MIB1: Contains 8 levels that correspond to 8 different types of objects and can be detailed on network: System (Operating system Information, this level is optional) Interfaces (Show as the devices are connected to network, this level is obligatory when the SNMP version2 is used; and it’s optional on version3) Address Translation (Maps the networks address to the physical addresses) Internet Protocol (IP) (Packages controller, obligatory) Internet Control Message Protocol (ICMP), (Types of used massage, obligatory) Transport Control Protocol (TCP), (Open connections, obligatory on TCP connections) User Datagram Protocol (UDP), (Closed connections, obligatory on UDP connections) Exterior Gateway Protocol (EGP), (Used to exchange routing information among autonomal systems) MIB2: Contains the same 8 before levels (ENHANCED): but with 3 new levels which are: TRANSMITION, SNMP, and CMOT. The rules describe the MIB objects are implemented by SMI that uses the ASN.1, It is the descriptive language, the objects, and descriptions are composed by the next components: description of the objects, syntax, definition, status. The SNMP uses two types of massages, the pooling whose objective is asking and answering , this effect to performance of the networks and it works by the 161 port and the method of interruption (Traps) This only handles the message of error or the network alarms , it works on 162 port.