I have just seen this, that I thought was an old problem, show up again..
I noticed it when I let a domU stay on DHCP long enough to try to do a renew,
then the
DHCP server started logging about checksum errors:
dhcpd: 5 bad udp checksums in 5 packets
DHCP server is 1:9.6.ESV.R4+dfsg-0+lenny1 so newer DHCP releases may contain
workaorunds
allowing these packets..
Since I had this problem years ago when I started with Xen I knew what to test
and doing
'ethtool -K eth0 tx off' on the domU fixes the checksumming problem.
I see this behavior between domU's using the same dom0 bridge on the same xen
host. And I
have tested between two Debian Squeeze domU's + one domU with 2.6.38 kernel.
Easiest way to reproduce seems to be with DNS (tried hping3 -2 ... but it DID
send correct
udp checksums even with tx-checksumming turned on).
Sniffing on a server (not necessarily running a DNS server, but pointed to in
the other
domU's resolv.conf):
# tcpdump -nnpvvi eth0 port 53
tcpdump: listening on eth0, link-type EN10MB (Ethernet), capture size 65535
bytes
10:41:48.733499 IP (tos 0x0, ttl 64, id 1644, offset 0, flags [DF], proto UDP
(17), length 59)
192.168.20.16.38961 > 192.168.20.96.53: [bad udp cksum 66ce!] 43518+ A?
aoeu.example.com. (31)
Then after doing 'ethtool -K eth0 tx off':
10:42:14.615619 IP (tos 0x0, ttl 64, id 8116, offset 0, flags [DF], proto UDP
(17), length 59)
192.168.20.16.52914 > 192.168.20.96.53: [udp sum ok] 44811+ A?
aoeu.example.com. (31)
Regarding the setup it's all on Debian Squeeze (except for the DHCP server I
first saw the
issue on).
# xm info
host : dom0
release : 2.6.32-5-xen-amd64
version : #1 SMP Tue Mar 8 00:01:30 UTC 2011
machine : x86_64
nr_cpus : 4
nr_nodes : 1
cores_per_socket : 4
threads_per_core : 1
cpu_mhz : 3013
hw_caps :
178bf3ff:efd3fbff:00000000:00001310:00802001:00000000:000037ff:00000000
virt_caps : hvm
total_memory : 3965
free_memory : 674
node_to_cpu : node0:0-3
node_to_memory : node0:674
node_to_dma32_mem : node0:674
max_node_id : 0
xen_major : 4
xen_minor : 0
xen_extra : .1
xen_caps : xen-3.0-x86_64 xen-3.0-x86_32p hvm-3.0-x86_32
hvm-3.0-x86_32p
hvm-3.0-x86_64
xen_scheduler : credit
xen_pagesize : 4096
platform_params : virt_start=0xffff800000000000
xen_changeset : unavailable
xen_commandline : placeholder dom0_mem=512M vga=gfx-1024x768x8
cc_compiler : gcc version 4.4.5 (Debian 4.4.5-10)
cc_compile_by : waldi
cc_compile_domain : debian.org
cc_compile_date : Wed Jan 12 14:04:06 UTC 2011
xend_config_format : 4
dom0 kernel:
Linux dom0 2.6.32-5-xen-amd64 #1 SMP Tue Mar 8 00:01:30 UTC 2011 x86_64
GNU/Linux
domU kernel:
Linux domU 2.6.32-5-xen-amd64 #1 SMP Tue Mar 8 00:01:30 UTC 2011 x86_64
GNU/Linux
domU with 2.6.38 vanilla kernel also showing the same problem:
Linux domU-2.6.38 2.6.38 #1 SMP Wed Mar 16 07:19:51 CET 2011 i686 GNU/Linux
After a short discussion on ##xen Pasi asked me to post the details here..
If I can contribute with more information just let me know.
I don't know whether the problem has been in my setup a long time or not, or
even if it
persists after a reboot of the xen host. Not doing any reboots right now anyway.
Hope someone understands why this happens (again)..
Thanks for any help and/or information about this.
/Sunkan
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