How to calculate the TCP/IP checksum?

NTDEV
1

Hi :
Now I am trying to modify the cloned net buffer list in my callout(windows vista),and I notice I should re-calculate the IP checksum. I wonder whether there are some fuctions in WDK to do this(calculate the TCP/IP checksum). Expect your help!
Thank you!!!

wunan

2

Google for “in_cksum”.

Thomas F. Divine

-----Original Message-----
From: xxxxx@lists.osr.com [mailto:bounce-282454-
xxxxx@lists.osr.com] On Behalf Of nanwu1984@163.com
Sent: Monday, April 02, 2007 11:22 AM
To: Windows System Software Devs Interest List
Subject: [ntdev] How to calculate the TCP/IP checksum?

Hi :
Now I am trying to modify the cloned net buffer list in my
callout(windows vista),and I notice I should re-calculate the IP
checksum. I wonder whether there are some fuctions in WDK to do
this(calculate the TCP/IP checksum). Expect your help!
Thank you!!!

wunan

Questions? First check the Kernel Driver FAQ at
http://www.osronline.com/article.cfm?id=256

To unsubscribe, visit the List Server section of OSR Online at
http://www.osronline.com/page.cfm?name=ListServer

3

If you’re just modifying the checksum in-place, there’s code in RFC
1631 (http://www.faqs.org/rfcs/rfc1631.html) that will do the job.
It’s a little faster and more convenient than re-running the checksum
over the entire packet.

Incidentally, you may need to modify more than just the IP datagram
checksum, depending on the transport layer in question. The NAT RFC
above goes into more detail on that point.

-sd

On Apr 2, 2007, at 10:22 AM, nanwu1984@163.com wrote:

Hi :
Now I am trying to modify the cloned net buffer list in my
callout(windows vista),and I notice I should re-calculate the IP
checksum. I wonder whether there are some fuctions in WDK to do
this(calculate the TCP/IP checksum). Expect your help!
Thank you!!!

wunan

Questions? First check the Kernel Driver FAQ at http://
www.osronline.com/article.cfm?id=256

To unsubscribe, visit the List Server section of OSR Online at
http://www.osronline.com/page.cfm?name=ListServer