Hello All,

I am using Ubuntu 12.04 and I need help on compiling kernel source by removing TCP options.

To simulate some specific scenario, I have to remove TCP Options filed in SYN ACK mesage. i.e Outgoing SYN-ACK message should not include TCP Options filed.

I have downloaded linux kernel source package after following below link.

https://wiki.ubuntu.com/Kernel/BuildYourOwnKernel

Now, I need help to understand what files needs to be modified and what section need to be modified in those files in-order to make ubuntu not send TCP Options filed in SYN-ACK message.

Any little help is greatly appreciated

Can you tell us what your overall goal is? Disabling/crippling TCP seems like a real bad idea.

SYN-ACK is part of the three way handshake needed to set up a TCP connection. Removing it (if at all possible) will cripple TCP. TCP is needed on a Linux box, networked or not. Some programs (X being one) depend on it even when the box isn't networked.

Anyway: The Networking support -> Networking options section in the menuconfig has many TCP related options, but none of them can specifically disable SYN-ACK (it is an integrate part of TCP).

Hello druuna,

I have to recreate the problem faced by one of my customer.
He is using a video server where SYN ACK sent by his server during TCP 3-way handshake doers not include TCP Option field. Due to this my gateway is doing more fragmentation of application messages which is resulting in no messages seen at the client.

Since my customer server is sending SYN ACK without TCP Option field I guess there is no harm in excluding in my server kernel.

Any help?

I'm not a network specialist, but it seems that the server in question might be restrictive in the way the handshake is performed (this can only be confirmed by analysing tcpdump output).

I don't think you need to re-compile the kernel, you might be able to manipulate the way things are done on your site by (un)setting one or more of the net.ipv4.tcp* options available from sysctl

I have to be honest and say that I would not know exactly which ones and what the proper values would be.

Only advise I can give you: Do a net search on SYN ACK tcp option field

EDIT: Maybe this article could be of use to you: RFC 4413 - TCP/IP Field Behavior (especially 4.2 / 4.3)