Hi,
I have an ipf firewall between two bridged interfaces of the machine.
When I introduce a redirect rule, the IP address and port of the
destination are modified properly, BUT the IP heqder checksum is not
recomputed. As a result the packet cannot be received by the other end
as it has an invalid checksum.
Original packet:
13:30:29.573313 0:e:c:5c:3a:a4 0:e0:29:3e:34:4e ip 78:
banyan.cs.ait.ac.th.52711 > 192.41.170.253.http: S 1521288476:1521288476(0) win
65535 <mss 1460,nop,nop,sackOK,nop,wscale 1,nop,nop,timestamp 16574672 0> (DF)
[tos 0x10]
0x0000 4510 0040 b0df 4000 4006 b472 c029 aa05 [EMAIL
PROTECTED]@[EMAIL PROTECTED])..
0x0010 c029 aafd cde7 0050 5aad 051c 0000 0000 .).....PZ.......
0x0020 b002 ffff 48dc 0000 0204 05b4 0101 0402 ....H...........
0x0030 0103 0301 0101 080a 00fc e8d0 0000 0000 ................
Redirected packet.
13:30:29.573421 0:e:c:5c:3a:a4 0:e0:29:3e:34:4e ip 78:
banyan.cs.ait.ac.th.52711 > 192.41.170.251.http: S 1521288476:1521288476(0) win
65535 <mss 1460,nop,nop,sackOK,nop,wscale 1,nop,nop,timestamp 16574672 0> (DF)
[tos 0x10]
4510 0040 b0df 4000 4006 b472 c029 aa05
^^^^ here is the checksum
c029 aafb cde7 0050 5aad 051c 0000 0000
^^^^ ^^^^ IP Destination
b002 ffff 48de 0000 0204 05b4 0101 0402
0103 0301 0101 080a 00fc e8d0 0000 0000
See both checksum are the same, which should not be as the IP
destination are different.
TIA
Olivier
