Jan Engelhardt skrev:
On Wednesday 2009-03-25 20:56, Kristian Evensen wrote:
Jan Engelhardt skrev:
On Wednesday 2009-03-25 20:47, Kristian Evensen wrote:
However, I have noticed a similar problem when using my module on incoming
packets in PREROUTING (on the multihomed receiver), the IP adress is changed
(accoring to my dmesg-output) but then they are not heard from again.
Probably dropped due to L3 or L4 checksum mismatches. While we try to
change the checksum, I have not verified it for all cases.
Hm, I am noe sure. I recalculate the checksum (using csum_replace4 for l3 and
inet....replace4 for l4) after modifying the destination IP, and when used with
OUTPUT the checksum is correct. Since tcpdump/Wireshark outputs the packets
before they are modified I haven't been able to verify this though.
You can use hexdump in the xtables module, or any other form, to
dump the checksum.
I had completely forgot that, thank you. However, tcpdump tells me that
the checksum is ok, but I will look into it and simply compare a packet
that has not been redirected with one that has. Thank you.
-Kristian
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