Data Link Layer

MAC (Media Access Control) addresses are globally unique addressed that are written into hardware at the time of manufacture. 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).

Spanning-Tree Protocol (STP) as defined in the IEEE 802.1D is a link management protocol that provides path redundancy while preventing undesirable loops in the network. For an Ethernet network to function properly, only one active path can exist between two stations. Loops occur in networks for a variety of reasons. The most common reason you find loops in networks is the result of a deliberate attempt to provide redundancy - in case one link or switch fails, another link or switch can take over.

A VPN is a service that offers secure, reliable connectivity over a shared public network infrastructure such as the Internet. VPNs maintain the same security and management policies as a private network. They are the most cost effective method of establishing a virtual point-to-point connection between remote users and an enterprise customer's network.

Data link layer iz divided mac layer and LLC layer.

This LLC LAYER is form for NOVELL AND IPX protocol.

For ip protocol we ve SRC ADDRESS and DEST ADDR(for

communication),but wen we uses IPX/NOVELL protocol the

frame include 1 more byte named "don know"(through which

communication happens @ 2nd layer)....(inshort to

communicate wid IP and IPX/NOVELL we form LLC layer.)

The Data Link Layer transforms the physical layer, a raw transmission facility, to a reliable link and is responsible for node-node delivery.

a. Framing

b. Physical Addressing

c. Flow Control

d. Error Control

e. Access Control

Virtual Private network is a network that used the public telecommunication infrastructure. This means that it used public wires to connect the nodes. E.g. Internet. VPN supports remote access to computers and allow data to be transmitted over this public network. Even though the data is transmitted over a public network, encryption and decrypting data to ensure security.