[Xen-bugs] [Bug 447] dom0 netfilter DNAT rule that rewrites the destination port doesn't work with domU TX checksum offload

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http://bugzilla.xensource.com/bugzilla/show_bug.cgi?id=447





------- Additional Comments From eggdrop@xxxxxxxxx  2005-12-31 20:08 -------
I can confirm this behaviour.

Below you'll find a tcpdump. Note the bad checksum in packet 4. 192.168.1.1 is
the IP of the bridge and 192.168.1.2 is the virtual machine.

I did "nc -l -p 2000" on the virtual machine and "telnet 192.168.1.2 2000" on 
xen0:

20:42:33.410533 IP (tos 0x10, ttl  63, id 18592, offset 0, flags [DF], proto:
TCP (6), length: 60) 192.168.1.1.42780 > 192.168.1.2.2000: S, cksum 0xc6c2
(correct), 2674143109:2674143109(0) win 5840 <mss 1460,sackOK,timestamp 35874597
0,nop,wscale 2>
20:42:33.410606 IP (tos 0x0, ttl  64, id 0, offset 0, flags [DF], proto: TCP
(6), length: 60) 192.168.1.2.2000 > 192.168.1.1.42780: S, cksum 0x65a6
(correct), 967998467:967998467(0) ack 2674143110 win 5792 <mss
1460,sackOK,timestamp 568189 35874597,nop,wscale 2>
20:42:33.410942 IP (tos 0x10, ttl  63, id 18593, offset 0, flags [DF], proto:
TCP (6), length: 52) 192.168.1.1.42780 > 192.168.1.2.2000: ., cksum 0xa559
(correct), 1:1(0) ack 1 win 1460 <nop,nop,timestamp 35874597 568189>

Then I try send a packet from xenU to xen0:

20:42:34.451945 IP (tos 0x0, ttl  64, id 55161, offset 0, flags [DF], proto: TCP
(6), length: 53) 192.168.1.2.2000 > 192.168.1.1.42780: P, cksum 0x837b
(incorrect (-> 0x9af3), 1:2(1) ack 1 win 1448 <nop,nop,timestamp 568294 
35874597>
20:42:34.452261 IP (tos 0x10, ttl  63, id 18594, offset 0, flags [DF], proto:
TCP (6), length: 52) 192.168.1.1.42780 > 192.168.1.2.2000: ., cksum 0xa0dd
(correct), 1:1(0) ack 2 win 1460 <nop,nop,timestamp 35875639 568294>

"ethtool -K eth0 tx off" fixes the problem.


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