Q:
OSI Layer
What is the difference between layer 2 and layer 3 in the OSI model?
ASKED:
Sep 10 2008 4:37 AM GMT
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A:
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The layer2 is called as data link layer which deals with data below the network layer that is layer 3. Layer2 deals with MAC addresses and layer 3 deals with the IP addreses. This is a major differnce.
Hope this will help you.
You may also wish to visit this other OSI Model answer on IT Knowledge Exchange.
The above answer is in fact correct. If I may elaborate just a bit. In order for two devices that are directly connected to one another over a medium (copper, fiber, air, etc) to communicate they must place the data, typically an IP packet, inside of a "layer two package" called a frame. These frames identify the sender and receiver with source and destination addresses. In a LAN (typically ethernet environment) this layer 2 address is referred to as a MAC address. As traffic moves through an interconnected network it typically passes across gateways or routers which are used to connect the networks of devices or wires to one another. When a router receives a frame with its address as the destination it opens it, looks at the layer three address (IP address usually) and compares it to a list of networks that it knows about. This list is called a forwarding or routing table. This table is used by the router to make a decision about what interface to forward the traffic out of to get to the destination network. It repackages the layer 3 packet in a new frame based on the exit interface type and places the layer 2 address of the directly connected device in the destination field. The new frame (containing the original data packet) is then passed to the next directly connected device where the process is repeated until the traffic reaches it's ultimate destination. I hope that this is clear without being more info than you needed.
Yours,
Brent Mossberger, CCSI
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