Ligações VPN(virtual private network)

[Gurzi]

Boas malta, programadores de esta pequena futura grande comunidade.

Ontem á conversa com uma senhora, rapariga de 20's a fisica e matematica, rapariga essa que estuda informatica sabe C melhor que ninguem e VB e de redes nem se fala e começou a falarme destas VPN só que nao percebi como é que é feita a encriptação visto que ela para se connectar á faculdade nao precisa de por nenhuma password.. como é que o server consegue saber que o client é user da escola ? :\

[thranduil]

pelo mac? :S nao sei.. e uma hipotese...

[perdido_e_sozinho]

Se o login do computador corresponder ao login usado na faculdade, não precisa de password adicional. Outra hipótese é como disse o thranduil é o mac adress da placa.

[Gurzi]

pois mas então ela tem que ou fornecer o mac adrress ou o login do computador... tava a ver que não era do nada que o server autenticava o client

mac adress :

Short for Media Access Control address, a hardware address that uniquely identifies each node of a network. In IEEE 802 networks, the Data Link Control (DLC) layer of the OSI Reference Model is divided into two sublayers: the Logical Link Control (LLC) layer and the Media Access Control (MAC) layer. The MAC layer interfaces directly with the network medium. Consequently, each different type of network medium requires a different MAC layer.

On networks that do not conform to the IEEE 802 standards but do conform to the OSI Reference Model, the node address is called the Data Link Control (DLC) address.

What Is a MAC Address?

The MAC address is a unique value associated with a network adapter. MAC addresses are also known as hardware addresses or physical addresses. They uniquely identify an adapter on a LAN.

MAC addresses are 12-digit hexadecimal numbers (48 bits in length). By convention, MAC addresses are usually written in one of the following two formats:

MM:MM:MM:SS:SS:SS

MM-MM-MM-SS-SS-SS

The first half of a MAC address contains the ID number of the adapter manufacturer. These IDs are regulated by an Internet standards body (see sidebar). The second half of a MAC address represents the serial number assigned to the adapter by the manufacturer. In the example,

00:A0:C9:14:C8:29

The prefix

00A0C9

indicates the manufacturer is Intel Corporation.

Why MAC Addresses?

Recall that TCP/IP and other mainstream networking architectures generally adopt the OSI model. In this model, network functionality is subdivided into layers. MAC addresses function at the data link layer (layer 2 in the OSI model). They allow computers to uniquely identify themselves on a network at this relatively low level.

MAC vs. IP Addressing

Whereas MAC addressing works at the data link layer, IP addressing functions at the network layer (layer 3). It's a slight oversimplification, but one can think of IP addressing as supporting the software implementation and MAC addresses as supporting the hardware implementation of the network stack. The MAC address generally remains fixed and follows the network device, but the IP address changes as the network device moves from one network to another.

IP networks maintain a mapping between the IP address of a device and its MAC address. This mapping is known as the ARP cache or ARP table. ARP, the Address Resolution Protocol, supports the logic for obtaining this mapping and keeping the cache up to date.

DHCP also usually relies on MAC addresses to manage the unique assignment of IP addresses to devices.

[thranduil]

hmm tu nao forneces directamente o teu mac. por exemplo, quando tu estas na internet e estas a fazer a comunicaçao com algum servidor, tu es procurado pelo ip e mac. nao sei se me fiz entender mas eu percebo isto mais ou menos so que nao te consigo e explicar bem porque tambem nao percebo muito de redes e tal. mas tu nao forneces directamente o teu mac. podes mas normalmente nao se faz isso.

[Gurzi]

entao quando eu dou o meu login na escola tenho que dar o mac adress nao ? o que nao entendo é como é que o server identificame , se nao der informaçao nenhuma tanto posso ser eu ou tu a entrar