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"IP addresses are used on layer 3 to identify machines throughout different networks" is this technically incorrect since you would also need a MAC address to identify the machines within the network?

IP addresses are used on layer 3 to identify networks and MAC addresses are use to identify machines in that network. Is this correct?

  • The correct answer to the question hinges on what exactly you mean by "identify"; please be explicit about why you're trying to identify a machine and how you will use the answer – Mike Pennington May 10 '15 at 14:03
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IP address take you to the network. and MAC will take you to Computer/node. and Port will take you to process. These all layers are required for communication for internet,

Better to make your Question more clear. What you really want to ask.

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IP addresses are used on layer 3 to identify machines throughout different networks

This is a correct statement.

is this technically incorrect since you would also need a MAC address to identify the machines within the network?

No, MAC addresses do not exist at layer 3, therefore they cannot carry any consideration at layer 3. If you were discussing networking in general or were including layer 2, then you might have some basis behind your statement. But the original statement specifically identifies this as layer 3.

Further, MAC addresses are not required at all if the layer 2 protocol doesn't need them. So while layer 2 MAC addresses exist in the vast majority of cases, you could have an IP address without a MAC address.

The use of technologies like NAT can muddy the issue a bit, but the general principle still holds true.

IP addresses are used on layer 3 to identify networks and MAC addresses are use to identify machines in that network. Is this correct?

No. IP addresses are used to identify devices or hosts, not networks. Therefore they do not identify networks. However, IP address ranges can be used to identify networks.

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The definition is correct. On layer 3, IP addresses are used to identify machines throughout different networks. Basically you can think of it like this:

  • An IP address is used to identify a host across multiple networks.
  • A MAC address plus IP address is used to identify a host within a network.

If you are talking to a machine on a different network, you only need to know the IP address. If you are communicating with a machine on your local network segment, you need to know the IP address and the MAC address.

  • I like where this is going. To put a point on it, layer 3 only concerns itself with IP addresses, and in fact some lower layers besides Ethernet do not use MAC addresses so it is incorrect to even suggest (as the OP does) that you can reliably identify a host by using a combination of the IP and the MAC. – Jeff Meden May 11 '15 at 17:37
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Network is the keyword. A network can be a higher-level concept, as in social network. So, technically (as in semantics) the first sentence of your post is correct.

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    'Social Network' on a network engineering site? Am I missing something? – cpt_fink May 10 '15 at 16:34
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    Yes. You are. Network is a concept that is not exclusive to Ethernet or IP. – Ron Royston May 10 '15 at 19:08
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    The context in the question didn't even remotely imply "social networks". – Jordan Head May 11 '15 at 6:12

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