Hi
I am modifying FreeBSD 4.1 kernel. I am hacking all UDP packets in
ip_input, changing some headers and finding the udp checksum
using in_pseudo() and setting the packet header csum_flags to
CSUM_UDP (I know this is a dirty way of doing it.. but, had to do it
for efficiency reasons). When I try to see the checksum after the checksum
calculation is complete in ip_output, I am getting the checksum
65535(0xffff). Is this a special checksum(error or something like
that..)? I have seen INVERT doing something like this in the file
/sys/alpha/alpha/in_cksum.c.
sum == 0xffff ? 0xffff : ~sum & 0xffff.
After modifying the packet in ip_input(), I call ip_forward() and the
packet should go and reach the intended destination as usual. But, this
destination address is the one that is changed in ip_input(). But, the
destination host is not getting the packet. I think this is a checksum
problem.
Could anyone please tell me what checksum 0xffff means, or give me some
pointers to where I can find this information?
Also, could anyone tell me if there are any csum_flags other than
CSUM_UDP and CSUM_DELAY_DATA in the mbuf packet header that can be set
before a udp packet reaches ip_output()?
thanks in advance.
regards
Madhavi.
To Unsubscribe: send mail to [EMAIL PROTECTED]
with "unsubscribe freebsd-hackers" in the body of the message
