Hi
I need to insert some data to IP packet.
We have TCP option field in TCP header which some option kind is reserved.
Can i use option kind of 31 (it is reserved) for my purpose?

this is a link to TCP parameters
http://www.iana.org/assignments/tcp-...parameters.xml

If i want to insert 32 bytes data to option field what problem does appear ?

for example
TCP option kind : 31
TCP option Length : 32 bytes

I know that maximum TCP header size is 60 bytes, it means 40 bytes option is allowed which i want to employ 32 bytes of this 40 bytes for my purpose.

Is it possible to do this ?

I know that I probably wouldn't attempt to monk-around with stuff at this low level. I detect an "XY Problem" here. What are you trying to accomplish?

Dear sundialsvcs
It is simple, i have a linux box.
The problem is how can I write into tcp option my custom data or how can write into IP option field my custom data ?

Nothing more

Okay, but why would you do that?

Ok
My linux box acts as a router and I need to insert some data into Option field of the IP packet.
And for this purposes I need to perform it in kernel for performance considerations.
Assume i want to insert origin source IP address of the packets in option field.

is it needed to describe more ?
best

Not really, because the source IP is already part of the IP header, and a router isn't supposed to change it.

Dear NevemTeve
Think the IP address is spoofed and i want to insert closest router IP address into the option field.
I know the routers just have to forward packets but i want to insert the IP address of the closest router to the source of packets into the option field for experimental purposes.
can I do that ?

Think i am testing a project in my labratory and i connect 5 PC together.
3 of them are linux router.

This might have something to do with 'iptables -t mangle'...

No it can't
We can change the TTL and QoS by iptables (i think).
It can't help for my purpose.
just can u tell me what IP option number 10 do ?
the link :

http://www.iana.org/assignments/ip-p...rameters.xhtml

the line bellow :

0 0 10 10 ZSU - Experimental Measurement [ZSu]

I've never said there is a complete solution to this problem, only that it has something to do with mangling; most likely you have to hack the kernel and/or (most likely and) create new iptables module(s).

Here's a URL to a (legitimate) web-page which basically describes the sort of thing that you are doing:

http://blogs.citrix.com/2012/08/31/u...-ip-insertion/

Incidentally, routers very often strip unrecognized information from headers. Use of an IP option-number (31) which is not in the published spec would almost certainly cause that element to be removed.

Dear NevemTeve
Thanks to answer.
I've studied the solution you mentioned.

Dear sundialsvcs
At the first post i have mentioned TCP option-number (31) which is exist and it is reserved.
Then i mentioned to IP header option-number (10) which is for experimental measurement.