Look at the Ethernet header below. Explain the following fields in the Ethernet

Question

Look at the Ethernet header below. Explain the following fields in the Ethernet header.

Preamble:

Destination Address:

Length:

Data:

FCS:

You are the most recently hired network engineer out of a group of 10 network engineers. During a meeting to implement a new switching technology, your manager asks the team to decide on which switching forwarding technique to use—cut-through or store-and-forward. You are required to come up with advantages and disadvantages of using both cut-through and store-and-forward. What would your list entail? Provide support for each item in your list.

Explain how each of the following commands below will impact the switched network? Which command is the default command used when setting up port-security on a Cisco switch?

switchport port-security violation protect

switchport port-security violation shutdown

switchport port-security violation restrict

Explanation / Answer

Answer :

1)

Preamble: This is seven bytes long and it consists of a pattern of alternating ones and zeros, and this informs the receiving stations that a frame is starting as well as enabling synchronisation.

Destination Address: In this field contains the address of station for which the data is intended. The left most bit indicates whether the destination is an individual address or a group address. An individual address is denoted by a zero, while a one indicates a group address. The next bit into the DA indicates whether the address is globally administered, or local. If the address is globally administered the bit is a zero, and a one of it is locally administered.

Length:- It provides MAC information and indicates the number of client data types that are contained in the data field of the frame.This field is two bytes in length. It may also indicate the frame ID type if the frame is assembled using an optional format.

Data: If the length of the field is less than 46 bytes, then padding data is added to bring its length up to the required minimum of 46 bytes.In this block contains the payload data and it may be up to 1500 bytes long.

FCS - It contains a 32 bit Cyclic Redundancy Check which is generated over the DA, SA, Length and Data fields.This field is four bytes long.

3)

Switchport port-security violation protect :This command silently drops traffic that is in violation until the number of secure addresses drop below the maximum value.

Switchport port-security violation shutdown: This command immediately puts the port into the "error-disabled" state, drops all traffic, and sends a SNMP trap notification.

Switchport port-security violation restrict : This command  behaves like protect but also increments the security violation counter for each violation and sends a SNMP trap notification.

The default command used when setting up port-security on a cisco switch is Switchport port-security violation shutdown.

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