Ethernet Introduction for CCNA R&S

Hello Himanshu

Let me refer you to a previous answer in this thread:

Now concerning your specific question: How will an IEEE802.3 frame know what the upper layer protocol in use is if this field is used as a length field? Remember that the Data Link layer is composed of two sub-layers, the Media Access Control (MAC) layer and the Logical Link Contro (LLC) layer. The LLC layer can add an additional header extension to an Ethernet frame called a SubNetwork Access Protocol (SNAP) header. This SNAP header includes things like an organization code and an Ether Type code which tells the device what upper layer protocol is being used.

Keep in mind that this information is beyond the scope of a CCNA R&S exam.

I hope this has been helpful!


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