How can I find the TCP packet length?

[verilog_crack]

TCP Length

Hi,
Can you tell me how can I find the TCP packet length.
You know UDP has a UDP packet length, so where is TCP length.
May be you tell me, I can use the IP packet length but I prefer a way for it in the TCP header for processing incomming packets faster(and economically).
However if TCP doesn't have a packet length then
1)what happened with IP pads. So if IP packet has some padding, how can I find the end of the TCP packet.
2)So why there is a Packet length in UDP header?
regards

 

[cyr]

Re: TCP Length

Yes, I think you have to compute the length from the IP header. RFC 793 says:

The TCP Length is the TCP header length plus the data length in
octets (this is not an explicitly transmitted quantity, but is
computed).

You need other information from the IP header as well, like the src and dst IP (for checksum etc).

I don't think IP packets ever have padding in the payload, so that's not a problem...

 

[feiutm9898]

Re: TCP Length

Can you tell me how can I find the TCP packet length.
You know UDP has a UDP packet length, so where is TCP length.
May be you tell me, I can use the IP packet length but I prefer a way for it in the TCP header for processing incomming packets faster(and economically).
However if TCP doesn't have a packet length then
1)what happened with IP pads. So if IP packet has some padding, how can I find the end of the TCP packet.
2)So why there is a Packet length in UDP header?
regards

Please see clearly at the photo below with color.

If you are design TCP/IP stack for embedded system, you need to do padding since Ethernet length have minimum of data length 46 bytes.

Try to use network analyzer to get the exact frame from network. Search Ethereal sofware.

The "length" is required to indicate the datagram length, if not, how a system know where to stop to capture the frame.