What is the minimum packet size for TCP over IPv4

Question

What is the minimum packet size for TCP over IPv4 ?

Hi guys, i am quite stuck on this very question.

Assume i wanna transmit a data of 12KB

and through IPv4 TCP

I did the following calculation

 20 Bytes for TCP Headers
 4 Bytes for Source Address
 4 Bytes for Destination Address
 4 Bytes on Zeros, Protocol and TCP Length
 2 Bytes on Checksum
 12 Bytes on Data

But i try check my friend result with mine, we get the different one..

I use the example on wikipedia on TCP, and i just assume

TCP header is 20Bytes and the calculation above ( i use all the TCP Pseudo Header that is pink ) .

What did i do wrong in my calculation. as 2 of my friends answer is 6 bytes more than me

My TCP header is 20 bytes IPV4 is 14 bytes Data is 12 Bytes

The only difference between us is my fren IPv4 is 20 bytes. which field did i do wrongly on my ipv4 calculation?

Thanks

@Caesar he got 20 for tcp header(same), 12 on data(same) and 20 on ipv4 which i only got 14 bytes for ipv4 — user1916580, Jan 25 '13 at 16:48
IPv4 frame got 20 bytes: [IPv4 frame](http://routemyworld.com/wp-content/uploads/2009/01/ipv4header.png) — Davide Berra, Jan 25 '13 at 16:54

score 2 · Answer 1 · answered Jan 25 '13 at 16:40

2

The minimum TCP header size is 20 bytes and the minimum IPv4 header size is 20 bytes. So a TCP/IPv4 packet containing 0 byte of data would be at the minimum 40 bytes assuming you can actually send 0 byte over TCP, which you can't. So, the minimum would be 41 bytes.

answered Jan 25 '13 at 16:40

Coincoin

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can tell me the minimum IPv4 header 20 bytes contain which headers? – user1916580 Jan 25 '13 at 16:43
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Of course you can send empty segments. You do that all the time, for example in the initial SYN or when ACK'ing while you don't have data to send. – Daniel Roethlisberger Jan 25 '13 at 16:54
quick search gave me this: http://nmap.org/book/images/hdr/MJB-TCP-Header-800x564.png – jeremy Jan 25 '13 at 16:56

score 2 · Answer 2 · edited Jan 25 '13 at 17:43

2

A quick Google search yields this diagram of the TCP header.

It looks like you're missing the following fields.

2 Bytes congestion window
4 bytes sequence
2 Bytes Urgent Pointer

Not sure which you are classifying as "Protocol", etc, but the main one missing looks like sequence number. Minimum should be 20 bytes for the TCP header.

edited Jan 25 '13 at 17:43

neirbowj

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answered Jan 25 '13 at 17:02

jeremy

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What is the minimum packet size for TCP over IPv4

2 Answers2