description for frame

[nnn_sss22]

Hello

Please define me header by header about frame headers. i m sending you image. find attachment.

And also tell me when this packet cross the trunk port then what header add the trunk port in this frame (for multiple vlans).Thanks

[Julio E. Moisa · Accepted solution]

Hi

Preamble: consists of 7 bytes, it is used by the receiver in order to enable the bit sync. 
Start of Frame: Basically indicates the beginning of the frame
Destination Address: is the Physical Address (MAC Address) of destination
Source Address: is the Physical Address (MAC Address) who originated the frame.
Tag protocol identifier or TPID: As I know it is used to identify the tag of a VLAN. Or distinguisher frames from other frames.
Tag control identifier or TCI: It can be used to prioritize or take action when there is congestion.
Type: indicates the type of data to immediately follow in the Data field
Data: Basically is the information transported to the destination.
Checksum sequence: is the method used to verify the integrity of the frame. It uses (CRC) algorithm to detect transmission errors.

[nnn_sss22]

Hello,

Frame is consist of these things which are below. right?

Destination Address: 6B 
Source Address: 6B
Type: 2B
Data: 1500B
Checksum sequence 4B

When Preamble and SFD will attached with the frame? thanks

[Jon Marshall · Accepted solution]

Not sure what you mean by what header will the switch add on a trunk port.

The packet format you have posted is for a tagged vlan ie. it is what the packet would look like when sent on a trunk port so there is nothing to add.

Jon

[Joseph W. Doherty]

As Jon notes, what you have listed is a tagged frame, which can support multiple VLANs.  The only kind of trunks that would further add to this frame would be Q-in-Q; tagged frames that contain tagged frames.

BTW, questions like your are often better handled on Cisco's learning network, i.e.: https://learningnetwork.cisco.com/welcome.

[nnn_sss22]

If we have only vlan 1 then additional header will not be added. 

When this packet cross the trunk port then which header will be add in the trunk port in this frame (for multiple vlans).

[Jon Marshall]

If it is a trunk link and the vlan is not the native vlan then the tag will be added to the header.

Jon

[nnn_sss22]

yes,if the vlan is not native vlan then these tags will be added which are below.

Tag protocol identifier or TPID

Tag control identifier or TCI

........................................................................................................................

Total frame size with VLAN Tag is 1530B

Without VLAN Tag, the frame size is 1526 B. right?

[Jon Marshall]

The tag is 4 bytes.

So the maximum frame size without a tag is 1518 and with a tag it is 1522.

Jon

[nnn_sss22]

Preamble: 7B

Start of Frame: 1B

Destination Address: 6B 
Source Address: 6B
Tag protocol identifier or TPID: 2B
Tag control identifier or TCI: 2B
Type: 2B
Data: 1500B
Checksum sequence 4B

when i calculate then it is 1530B with vlan tag and without vlan tag 1526B. 

How it is 1522B with vlan tag and 1518B without vlan tag?

[Jon Marshall]

The preamble and SFD (Start of Frame Delimiter) are not part of the frame.

Jon

[nnn_sss22]

Hello,

I have read some links even wikipedia. there is mention 1526B and with 1530B

i am also sending you one link

https://networkengineering.stackexchange.com/questions/5057/what-is-the-actual-size-of-an-ethernet-mtu

Please can you tell me if preamble and SFD are not part of the frame then what are these. thanks

[Jon Marshall]

If you are talking about the frame you do not include those first two fields.

There is something called Q-in-Q which is generally used by SPs and this involves the use of two 4 byte tags which would increase the maximum frame size to 1526.

I have no idea where the 1530 is coming from.

Jon

[nnn_sss22]

Hello,

Frame is consist of these things which are below. right?

Destination Address: 6B 
Source Address: 6B
Type: 2B
Data: 1500B
Checksum sequence 4B

When Preamble and SFD will attached with the frame? thanks