> update a piece of a packet 

IIRC you only need to update the IP header checksum
if you are altering part of the IP header.

--
aboyd

On Mon, Feb 02, 2009 at 10:15:18AM -0500, Jonathan Langen wrote:
> I'm working on an IP driver, mounted in io-net with the full TCP/IP stack, under QNX 6.3.2.  If I need to update a 
piece of a packet on its way through my driver, how should I recalculate the IP checksum?
> 
> I've read up on RFC 1071, dealing with calculating IP checksums, but if the stack already provides a way to update it 
for me, then I would rather use that then write one of my own.  Since updating the TTL is something that should be done 
on every hop, I was surprised when I couldn't find anything on it when searching the QNX/Foundry27 sites.  Perhaps this 
is typically only done by the stack and not by the drivers... but is there a way for a driver to do it?

Grep for IPTTLDEC (which is defined to 1) in the ipflow source.

-seanb

http://community.qnx.com/integration/viewcvs/viewcvs.cgi/*checkout*/trunk/sys/netinet/ip_flow.c?root=core_networking&rev
=480&system=exsy1001