[Xen-users] tcp checksum errors across dom0-domu bridge

[Daniel Goertzen <goertzen@xxxxxxxx>]

My xen setup is having trouble communicating between dom0 and domu.  The dom0 
and domUs have no problem communicating outside the physical machine, and the 
domUs can even talk to each other with no problems, but dom0-domU comms is a 
no-go.

I am running gentoo x86 and xen-3.0.0.  The xend network-bridge script didn't 
seem to work at all, so I disabled it and use a bridge configured by gentoo 
(see dom0 network info below).  The domUs use vanilla xend bridge networking 
(see dom1 network info below).

Now the dom0 and domU can ping each other, and even establish a tcp connection, 
but dom0->domU tcp packets always seem to have a failing checksum. (see tcpdump 
trace of a telnet session below)

Any thoughts?

Thanks,
Dan.


#######################################
# dom0 network information

dom0 / # brctl show
bridge name     bridge id               STP enabled     interfaces
br0             8000.005004652f84       no              eth0
                                                       vif3.0
dom0 / # ip a l dev br0
20: br0: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue
   link/ether 00:50:04:65:2f:84 brd ff:ff:ff:ff:ff:ff
   inet 192.168.1.5/24 brd 192.168.1.255 scope global br0
   <inet6 stuff omitted>
dom0 / # ip a l dev eth0
19: eth0: <BROADCAST,MULTICAST,PROMISC,UP> mtu 1500 qdisc pfifo_fast qlen 1000
   link/ether 00:50:04:65:2f:84 brd ff:ff:ff:ff:ff:ff
   inet6 fe80::250:4ff:fe65:2f84/64 scope link
      valid_lft forever preferred_lft forever
dom0 / # ip a l vif3.0
23: vif3.0: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue
   link/ether fe:ff:ff:ff:ff:ff brd ff:ff:ff:ff:ff:ff
   inet6 fe80::fcff:ffff:feff:ffff/64 scope link
      valid_lft forever preferred_lft forever

dom0 / # ip r l
192.168.1.0/24 dev br0  proto kernel  scope link  src 192.168.1.5
127.0.0.0/8 dev lo  scope link
default via 192.168.1.1 dev br0

dom0 / # arp -a
? (192.168.1.6) at 00:16:3E:6C:24:FC [ether] on br0
? (192.168.1.103) at 00:11:D8:5C:01:98 [ether] on br0
? (192.168.1.103) at 00:11:D8:5C:01:98 [ether] on br0
dom0 / # brctl showmacs br0
port no mac addr                is local?       ageing timer
 1     00:11:95:e2:7d:72       no                11.08
 1     00:11:d8:5c:01:98       no                 0.00
 2     00:16:3e:6c:24:fc       no                15.33
 1     00:20:af:50:15:9c       no                 8.32
 1     00:50:04:65:2f:84       yes                0.00
 1     00:90:4b:4b:6d:f6       no                99.14
 2     fe:ff:ff:ff:ff:ff       yes                0.00



#######################################
# dom1 network information

dom1 / # ip a l eth0
2: eth0: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast qlen 1000
   link/ether 00:16:3e:6c:24:fc brd ff:ff:ff:ff:ff:ff
   inet 192.168.1.6/24 brd 192.168.1.255 scope global eth0
   <inet6 stuff omitted>
dom1 / # ip r l
192.168.1.0/24 dev eth0  proto kernel  scope link  src 192.168.1.6
127.0.0.0/8 dev lo  scope link
default via 192.168.1.1 dev eth0
dom1 / # arp -a
? (192.168.1.5) at 00:50:04:65:2F:84 [ether] on eth0
? (192.168.1.103) at 00:11:D8:5C:01:98 [ether] on eth0
? (192.168.1.1) at 00:20:AF:50:15:9C [ether] on eth0




#######################################
# tcpdump of domU->dom0 telnet session
#
# Note that tcpdump running in dom0 and dom1 will both show the tcp checksum 
errors.
#

dom1 ~ # tcpdump -v -i eth0 port 23
tcpdump: listening on eth0, link-type EN10MB (Ethernet), capture size 96 bytes
17:54:21.182760 IP (tos 0x10, ttl  64, id 48589, offset 0, flags [DF], length: 60) 
192.168.1.6.33778 > 192.168.1.5.telnet: S [tcp sum ok] 1720050423:1720050423(0) win 
5840 <mss 1460,sackOK,timestamp 1728314 0,nop,wscale 2>
17:54:21.280506 IP (tos 0x0, ttl  64, id 0, offset 0, flags [DF], length: 60) 
192.168.1.5.telnet > 192.168.1.6.33778: S [tcp sum ok] 2896578887:2896578887(0) ack 
1720050424 win 5792 <mss 1460,sackOK,timestamp 11502518 1728314,nop,wscale 2>
17:54:21.280528 IP (tos 0x10, ttl  64, id 48591, offset 0, flags [DF], length: 52) 
192.168.1.6.33778 > 192.168.1.5.telnet: . [tcp sum ok] ack 1 win 1460 
<nop,nop,timestamp 1728315 11502518>
17:54:21.183846 IP (tos 0x10, ttl  64, id 48593, offset 0, flags [DF], length: 76) 
192.168.1.6.33778 > 192.168.1.5.telnet: P [tcp sum ok] 1:25(24) ack 1 win 1460 
<nop,nop,timestamp 1728315 11502518> [telnet DO SUPPRESS GO AHEAD, WILL TERMINAL 
TYPE, WILL NAWS, WILL TSPEED, WILL LFLOW, WILL LINEMODE, WILL NEW-ENVIRON, DO STATUS]
17:54:21.183905 IP (tos 0x10, ttl  64, id 51966, offset 0, flags [DF], length: 52) 
192.168.1.5.telnet > 192.168.1.6.33778: . [tcp sum ok] ack 25 win 1448 
<nop,nop,timestamp 11502518 1728315>
17:54:21.238656 IP (tos 0x10, ttl  64, id 51968, offset 0, flags [DF], length: 64) 
192.168.1.5.telnet > 192.168.1.6.33778: P [bad tcp cksum 838e (->f14)!] 1:13(12) ack 
25 win 1448 <nop,nop,timestamp 11502523 1728315> [telnet DO TERMINAL TYPE, DO TSPEED, 
DO XDISPLOC, DO NEW-ENVIRON]
17:54:21.439151 IP (tos 0x10, ttl  64, id 51970, offset 0, flags [DF], length: 64) 
192.168.1.5.telnet > 192.168.1.6.33778: P [bad tcp cksum 838e (->eff)!] 1:13(12) ack 
25 win 1448 <nop,nop,timestamp 11502544 1728315> [telnet DO TERMINAL TYPE, DO TSPEED, 
DO XDISPLOC, DO NEW-ENVIRON]
17:54:21.859153 IP (tos 0x10, ttl  64, id 51972, offset 0, flags [DF], length: 64) 
192.168.1.5.telnet > 192.168.1.6.33778: P [bad tcp cksum 838e (->ed5)!] 1:13(12) ack 
25 win 1448 <nop,nop,timestamp 11502586 1728315> [telnet DO TERMINAL TYPE, DO TSPEED, 
DO XDISPLOC, DO NEW-ENVIRON]




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