1

We know that the packet contains an IPv4 header, by reading the EtherType field. My question is, how does the NIC know the Layer 2 protocol is Ethernet to begin with? If there are two different Layer 2 protocols in the channel, how do you know which one you are dealing with?

5

A NIC is built for Ethernet. Or Fibre Channel. Or Wi-Fi. Or Bluetooth. Or (formerly) either FDDI, ATM, or ARCNET.

I don't think there's ever been a multi-protocol NIC outside a lab.

(Recently though, some storage NICs have become bi-lingual, Ethernet or Fibre Channel, depending on the SFP module fitted).

On the channel, you've only ever got a single L2 protocol. There's no way multiple protocols can coexist.

0

I think this is mentioned in Ethertype field of Ethernet Frame: https://en.wikipedia.org/wiki/EtherType

  • 1
    No. The EtherType field specifies the L2 payload type, ie. the layer-3 protocol or the one sitting right on top of L2. – Zac67 Oct 7 '18 at 13:43

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.