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by venkatramaiah.sudarsan

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hi friends,

while attending a ccna class i had doubt that if a switch or a NIC card is a layer 2 device and can recognise only mac-addresses, how can it accept an ip address.. when I asked this question, my faculty promptly turned down by just replying it as a stupid question.. I still dont have an answer for my question whether it is stupid or not.. can anyone come forward to help me out?

rgds
sudarsan

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by cg it

the data-link layer doesn't "accept" ip addresses. The data-link layer contains mac address and in the "frame" format. the packet header in the network layer contains a logical address and not a physical address [physical address being MAC and logical address being IP]. a switched network operates by MAC addresses not IP. switches have a table like routers do but switch tables are physical address tables. they view the data-link layer mac address of the frame, then consult the table to find out what port on the switch a particular mac address is. Then send the frame to that port.

understanding how a packet is assmebled and how it is disassembled on its way up and down the protocol stack and how the elements that make up a packet or frame or data gram and is read by the different protocols is key to understanding how each portion of the stack operates and how the entire stack functions. Though each protocol in the stack is dependent upon the protocol above and below, they also operate independently. e.g. its not just vertical up and down but horizontal as well. data-link talks to data-link, network to network, etc.

by cg it

an analogy is a letter within a letter within a letter within a package. The package being the final stage before being sent to the post office [the router]. Once the package is at the router, it's sent to the destination. There the package is received and opened, which the package contains a letter. That letter is read, and the enclosed letter is fowarded per the instructions of the cover letter. this process is repeated until the final destination is reaced via the MAC address at the data-link layer. The final destination {the application layer}opens the last letter and gets the payload. simplistic analogy but thats kinda how the process work. Wrappers aren't thrown alway rather only read to determine where to send it next.

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